Table of Contents. Section 3: Hazard Identification and Risk Assessment

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1 Table of Contents Introduction Hazard Identification Previous State Plans Disasters and Emergencies in Colorado State Declarations Federal Declarations Insured Losses Local Mitigation Plans Hazard Profiles Atmospheric Hazards Drought Extreme Heat Floods Hailstorms Lightning Precipitation Thunderstorms Tornadoes Windstorms Winter Weather Geologic Hazards Avalanche Earthquake Erosion and Deposition Expansive Soils Landslides, Mud and Debris Flow, and Rockfalls Subsidence Other Fire Grasshopper Infestation Vulnerability State Asset Exposure Local Jurisdictions Future Development Potential Losses State Asset Losses Local Jurisdictions Future Development Colorado Natural Hazards Mitigation Plan 3 1

2 Consequence Analysis Avalanche Drought Earthquake Erosion and Deposition Expansive Soils Fire Flood Grasshopper Infestation Hailstorms Landslides, Mud and Debris Flow, and Rockfalls Lightning Precipitation Subsidence Summertime: Extreme Heat Thunderstorms Tornado Windstorms Winter Weather Colorado Natural Hazards Mitigation Plan 3 2

3 RISK ASSESSMENT: 201.4(c)(2): [The State plan must include a risk assessment] that provides the factual basis for activities proposed in the strategy portion of the mitigation plan. Statewide risk assessments must characterize and analyze natural hazards and risks to provide a statewide overview. This overview will allow the State to compare potential losses throughout the State and to determine their priorities for implementing mitigation measures under the strategy, and to prioritize jurisdictions for receiving technical and financial support in developing more detailed local risk and vulnerability assessments. Introduction The purpose of the Hazard Identification and Risk Assessment (HIRA) is to identify natural hazards and to evaluate the risk to the State of Colorado, the health and safety of its citizens, property, and economy. A vulnerability and risk assessment is a decision support tool for determining the need for and prioritization of mitigation measures to protect assets and processes. While it is financially unfeasible to reduce risk from every natural hazard event, vulnerability and risk assessments can help ensure that the available resources and actions taken are justified and implemented based on the threat, vulnerability, and risk. Hazard identification and the assessment of associated risks is a shared responsibility between the state and local communities. Both the state and local communities assess the risks from hazards as part of their respective planning processes. While local governments focus on the hazards, vulnerabilities, and risks on a local or regional scale, the state focus remains on the regional and statewide implications of hazards. The HIRA is divided into the following sections, providing a detailed discussion of process, approach, and content: Introduction Hazard Identification Hazard Profiles Vulnerability Loss Estimates Consequence Analysis Colorado Natural Hazards Mitigation Plan 3 3

4 Hazard Identification Requirement 201.4(c)(2)(i): [The State risk assessment shall include an] overview of the type of all natural hazards that can affect the State. This section identifies the hazards that are probable, or based on future probability, likely to negatively impact the State of Colorado. The primary methods of determining which hazards to include in the 2010 State Plan update included the evaluations of: Previous State Plans Disasters and Emergencies in Colorado Insured Losses Local Mitigation Plans Review and analysis by the SHMT revealed the list of hazards from the 2004 plan remained relevant for the 2007 plan, as well as the 2010 plan update. In addition to hazards identified in previous planning processes, grasshopper infestation was included in the 2010 plan. Grasshopper infestation was added because it has previously been declared as a state disaster and it is called out in state legislation (SB 92-36). The natural hazards identified for Colorado and used for this risk assessment are: Avalanche Drought Earthquake Erosion and Deposition Expansive Soils Wildfire Floods Grasshopper Infestation Hailstorms Landslides, Mud/Debris Flows, Rockfalls Lightning Precipitation Subsidence Summertime: Extreme Heat Thunderstorms Tornadoes Windstorms Winter Weather Previous State Plans The 2004 State Hazard Mitigation Team (SHMT) reviewed all the natural hazards that FEMA has identified (FEMA publication 386-2, Understanding Your Risks: Identifying Hazards and Estimating Losses 2002) and determined which were of concern in Colorado. Coastal related hazards (costal erosion, costal storm, hurricane, and tsunami) and volcanoes were eliminated for consideration because of unlikely impact on the state. Dam failure is incorporated into the flood annex and is not addressed in this hazard identification. Colorado Natural Hazards Mitigation Plan 3 4

5 Disasters and Emergencies in Colorado Historic state and federal-level disaster or emergency declarations were reviewed to ensure coverage of events in the State Plan. These state and federal declarations are listed in the tables below as a consolidated set of data rather than including in each hazard profile section. State Declarations Colorado disasters and emergencies declared by the Governors from 1980 to early 2010 are shown in Table 3-1. Note the diversity in types of events declared: grasshopper infestation, drought, wildfires, tornadoes, rockfalls, floods, sinkholes, mudslides, and blizzards. Table 3 1: Disasters in Colorado, 1980 to 2010 Year Hazard Location 2010 Wildfire Larimer County 2010 Wildfire Boulder County 2010 Rockslide I Severe Blizzard Statewide 2009 Severe Spring Snowstorm Statewide 2008 Wildfires Crowley County 2008 Contamination of Water Supply Alamosa 2008 Severe Tornadoes in Northern CO Weld and Larimer Counties 2008 Fire Housetop Fire, Mesa County 2008 Wildfires Las Animas County 2007 Tornado Holly, Prowers County 2007 Tornadoes Prowers, Phillips, Cheyenne Counties 2007 Rockfalls I 70, US 6 Garfield, Clear Creek, Jefferson 2006 Snow Emergencies 2 Executive Orders December 24 counties 2006 Severe Winter Storm October Southern Colorado, including El Paso County 2006 Wildfires multiple Executive Orders Garfield, Teller, and Custer Counties 2006 Wildfire 2 Executive Orders Las Animas and Huerfano Counties, Costilla and Huerfano 2006 Drought South Platte Basin in Northern Colorado 2006 Flooding Douglas, Teller, Fremont, Pueblo, Garfield Counties 2005 Wildfire Pueblo and Custer Counties 2004 Wildfire Larimer County 2004 Tornadoes Logan County 2003 Sinkhole Interstate 70, Eagle County 2003 Wildfire Cherokee Fire 2003 Snow Emergency Statewide 2002 Wildfires Statewide 2002 Mudslides San Miguel County 2002 Drought All counties 2001 Severe Winter Storms Eastern Plains and Front Range counties Colorado Natural Hazards Mitigation Plan 3 5

6 Year Hazard Location 2000 Flood Elbert County 2000 Wildfires multiple Executive Orders Jefferson, Park, Boulder, Larimer, Las Animas 1999 Flood 2 Executive Orders Sedgwick County, Washington County 1999 Flooding, Landslides, Mudslides Bent, Crowley, Custer, El Paso, Elbert, Fremont, Kiowa, Larimer, Otero, Las Animas, Pueblo, Weld 1998 Landslides, Rockfalls Archuleta, Garfield, Mesa, Gunnison, Rio Blanco 1998 Wildfire Mt. Evans 1997 Blizzard 2 EOs in October, December South Central Colorado, Front Range East 1997 Landslides Jefferson County 1997 Flooding Fort Collins, Weld, Morgan, Logan, Phillips, Clear Creek, Elbert, Kiowa, Baca, Otero, Lincoln, Crowley, Prowers, Sedgwick County, Holyoke 1996 Tornadoes Morgan and Washington Counties 1996 Fire Buffalo Creek, Jefferson County 1996 Flood Buffalo Creek, Jefferson County 1996 Wildfire, Drought, Severe Weather Several Locations 1995 Flood Weld, Morgan Counties 1994 Flood Pueblo County, Lyons Boulder County 1994 Wildfires Garfield, Delta, Douglas, Jefferson, statewide 1992 Flood Fort Collins 1990 Hailstorm Denver, Boulder 1990 Wildfire Olde Stage Fire, Boulder County 1990 Severe Thunderstorm El Paso 1990 Tornado Limon 1990 Blizzard Several Locations 1989 Wildfire Black Tiger Fire, Boulder County 1989 Flooding Town of Rico 1988 Wildfire 3 Executive Orders Lefthand Canyon, Boulder County, Larimer County, Fremont 1988 Tornado Denver 1987 Wildfire Garfield 1987 Flood Mitigation Alamosa 1987 Wildfire Cheyenne, Lincoln, Elbert 1987 Flooding Park 1986 Earth Slide Delta 1986 Earthflow SH 133, N of Paonia Res Winter Storm Weld 1984 Severe Winter Storm Conejos County 1984 Water System Oak Creek, Routt County 1984 Flooding Delta, Dolores, Hinsdale, Saguache, Mesa, Montrose, Moffat, Rio Blanco, Pitkin, San Miguel, Ouray, Eagle, Gunnison, and Silt 1982 Severe Winter Storm Denver, Arapahoe, Adams, Jefferson, Boulder, El Paso, Weld 1982 Dam Failure Lawn Lake Dam, Larimer 1982 Flooding Ouray County 1981 Water System City of Trinidad and Vicinity 1981 Grasshopper Infestation Eastern Colorado Counties 1981 Dam Safety Adams, Weld 1981 Tornadoes Adams, Denver, Jefferson, Weld Colorado Natural Hazards Mitigation Plan 3 6

7 Year Hazard Location 1980 Grasshopper Infestation Logan, Morgan, Sedgwick, Phillips, Washington, Weld 1980 Flooding Weld, Logan, Washington, Morgan, Larimer, Sedgwick 1980 Severe Winter Storm Cheyenne, Kit Carson Federal Declarations Source: Colorado Division of Information Technology State Archives 2007 website Colorado has received seven presidential disaster declarations and three emergency declarations for events from 1980 through December 2009 as shown in Table 1-#. For the four recent presidential disasters and three emergency declarations since 1997, Colorado was awarded dollar amounts for Public Assistance (PA), Individual Assistance (IA), and the Hazard Mitigation Grant Program (HMGP) as shown in Table 3-2. Table 3 2: Presidential Disaster and Emergency Declarations, 1980 to 2009 Year Disaster Number Disaster Event Description 1982 DR 665 CO Estes Park Dam Break Flood 1984 DR 719 CO Western Slope Flooding 1997 DR 1186 CO Flood Disaster in Colorado 1999 DR 1276 CO Severe Storms, Flooding, Landslides and Mudslides 2001 DR 1374 CO Severe Winter Storms 2002 DR 1421 CO Wildfires Assistance Program Public Assistance Individual Assistance Hazard Mitigation Public Assistance Individual Assistance Hazard Mitigation Public Assistance Hazard Mitigation Individual Assistance Hazard Mitigation Federal ( Millions) Unknown EM 3185 CO Snow Emergency Public Assistance EM 3270 CO Snow Emergency 2006 EM 3271 CO Snow Emergency 2008 DR 1276 CO Severe Storms and Tornadoes Public Assistance 11.0 Individual Assistance Hazard Mitigation In addition to Presidential declarations, Colorado has received close to 50 fire assistance awards for suppression and management since 1978, as shown in Table 3-3. The most recent awards in 2010 included the worst wildland fire in state history in terms of destroyed or damaged property with over $200 million in insured loss. Colorado Natural Hazards Mitigation Plan 3 7

8 Table 3 3: FEMA Fire Suppression/Fire Management Assistance, 1978 to 2009 Year Fire Year Fire 1978 Deer Creek Canyon 2002 Million 1980 Bear Trap 2002 Wiley Ridge 1989 Sunnyside 2002 Grizzly Gulch 1990 Old Stage 2002 Again 1994 Wake Complex 2002 Burn Canyon 1994 South Canyon 2002 Big Elk 1994 Roxborough Complex 2002 Panorama 1996 Buffalo Creek 2003 Cloudy Pass 2000 Bobcat 2003 Lincoln Complex 2000 Hi Meadow 2003 Overland 2000 Eldorado 2003 Cherokee Ranch 2001 Armageddon Carter Lake 2003 Buckhorn Creek 2002 Snaking 2004 Picnic Rock 2002 Cuerno Verde 2004 McGruder 2002 Black Mountain 2005 Mason 2002 Schoonover 2006 Mauricio Canyon 2002 Iron Mountain 2006 Mato Vega 2002 Spring Trinidad Complex 2006 Red Apple 2002 Fisher Trinidad Complex 2007 Newcastle 2002 Ute Pass 2008 Ordway 2002 Coal Seam 2008 Nash Ranch 2002 Hayman 2009 Olde Stage 2002 Dierich Creek 2010 Fourmile Canyon 2002 Missionary Ridge 2010 Reservoir Road 2002 Valley Colorado also regularly receives United States Department of Agriculture (USDA) Secretarial Disasters. These declarations typically result from hail, windstorms, drought, early freezes, and grasshopper infestations. Table 3-4 shows Secretarial Disasters since 2003, however, years prior produced many additional declarations. Colorado Natural Hazards Mitigation Plan 3 8

9 Table 3 4: USDA Secretarial Disasters in Colorado, 2003 to 2009 Year Type Declaration Number Declaration Number and Affected Counties 2003 Drought S1797 Baca, Bent, Elbert, Kiowa, Lincoln, Prowers 2003 Drought, Insects S1843 Alamosa, Archuleta, Chaffee, Conejos, Costilla, Crowley, Custer, Dolores, Fremont, Garfield, Hinsdale, Huerfano, La Plata, Lake, Las Animas, Mesa, Mineral, Moffat, Montezuma, Otero, Pueblo, Rio Blanco, Rio Grande, Routt, Saguache 2003 Drought S1890 Cheyenne, Phillips 2004 Drought, Freeze, Hail S1947 Baca, Chaffee, Cheyenne, Custer, Eagle, Fremont, Garfield, Grand, Jackson, Kiowa, Kit Carson, Lake, Lincoln, Phillips, Pitkin, Prowers, Pueblo, Routt, Summit, Yuma 2004 Drought S2009 Moffat 2005 Drought S2031 Huerfano, Las Animas, Rio Blanco /6 2005/ Drought, Freezing Temperatures Drought, Wind, Heavy Rain, Hail Drought, Crop Diseases, Insect Infestation Drought, Crop Diseases, Insect Infestation Drought, Fire, High Winds, Heat Heat, high winds, insect pests, late freeze, drought Heat, high winds, drought S2160 S2188 S2217 S2287 S2327 S2329 S2351 Delta, Kit Carson Crowley, El Paso, Lincoln, Otero, Park, Phillips, Pueblo, Teller, Washington, Yuma Logan Huerfano, Kiowa, Las Animas, Sedgwick Adams, Alamosa, Baca, Broomfield, Chaffee, Cheyenne, Conejos, Costilla, Custer, Denver, Dolores, Douglas, Elbert, Fremont, Hinsdale, Huerfano, Kit Carson, Lake, Las Animas, Mineral, Montezuma, Morgan, Prowers, Pueblo, Rio Grande, Saguache, San Miguel, Weld Arapahoe, Archuleta, Bent, Boulder, Crowley, Delta, El Paso, Gunnison, Jefferson, Kiowa, La Plata, Montrose, Ouray, Park, Phillips, Teller, Washington Eagle, Garfield, Larimer, Logan, Otero, Pitkin, Rio Blanco, Yuma 2006 Drought S2382 Jackson, Lincoln, Mesa, Moffat 2006 Drought S2480 Sedgwick 2008 Drought S2750 Adams, Arapahoe, Baca, Bent, Cheyenne, Crowley, Douglas, El Paso, Elbert, Huerfano, Kiowa, Kit Carson, Las Animas, Lincoln, Logan, Otero, Park, Prowers, Pueblo, Teller, Washington, Weld 2008 Drought S2802 Fremont 2009 Drought S2970 Dolores, Mesa, Montezuma, Montrose, San Miguel Source: USDA Farm Service Agency Colorado Natural Hazards Mitigation Plan 3 9

10 Insured Losses Current insurance industry standards classify a catastrophe as a natural disaster that causes at least $25 million in insured damage. Colorado has experienced 16 such catastrophes since 1984, the majority representing significant hailstorm events as shown in Table 3-5. The most costly catastrophe in Colorado history is a hailstorm that hit the Front Range in July 1990 and caused $625 million in damage. Table 3 5: Colorado Disasters with High Insured Dollar Losses Year Natural Hazard At Time Of Loss Insured Loss (Millions) 2009 Dollars 1984 Hail Tornado (Limon) Hail , Hail Hail Hail Hail Hail Wildfires Winter Storm Hail Hail Tornadoes/Hail June 2009 Hail (Denver Metro) July 2009 Hail (Denver Metro) Hail (Pueblo) Wildfire 200* *Preliminary estimate Source: Rocky Mountain Region Insurance Statistics (Colorado Specific) Other costly disasters in Colorado include wildfires, winter storms, and tornadoes. Prior to 2010, the 2002 wildfire season in Colorado was the most expensive in state history. The overall estimated cost of the Iron Mountain, Coal Seam, Missionary Ridge and Hayman Fires in Colorado is $70.3 million in insured losses. Companies received 1,236 customer claims for the Hayman and Missionary Ridge Fires at a cost of around $56.4 million. The Fourmile Canyon Fire in September 2010 became the costliest fire in Colorado with a preliminary estimate of over $200 in insured losses. Additional events as considered catastrophes from an insurance industry perspective include the most expensive winter storm from snow and ice damage in Colorado history with the blizzard in March The estimated price tag from this storm was nearly Colorado Natural Hazards Mitigation Plan 3 10

11 $93.3 million from more than 28,000 claims filed. Also, in June of 1990, a tornado touched down in Limon, Colorado causing an estimated $20 million in insured damages. Local Mitigation Plans Local mitigation plans were reviewed for new natural hazards for this plan and remain consistent with the natural hazards addressed by this plan. See Section 6 - Counties and Communities for further information on hazards addressed by local planning efforts. Sources Rocky Mountain Insurance Information Association (RMIIA) United States Department of Agriculture (USDA), Farm Service Agency (FSA) Federal Emergency Management Agency (FEMA) Colorado State Archives Colorado Natural Hazards Mitigation Plan 3 11

12 Hazard Profiles Requirement 201.4(c)(2)(i): [The State risk assessment shall include an overview of the] location of all natural hazards that can affect the State, including information on previous occurrences of hazard events, as well as the probability of future hazard events, using maps where appropriate. Primary areas of consideration within hazard profiles in this plan are listed below. Hazard Analysis Summary Definition Characteristics Geographic Location Previous Occurrences Probability of Future Events Magnitude and Severity Previous versions of the plan included pertinent information to achieve complete hazard profiles but were structured in a manner that provided opportunity to enhance organization for the 2010 plan update. Each of the areas of consideration for the hazard profiles and assessment of risk are described below. Hazard Analysis Summary For each hazard, a rollup of the analysis is provided for reference and to use as a tool for determining which hazards may have precedence when it comes to allocating statewide mitigation resources. This hazard analysis summary provides an impact and associated description for geographic location, previous occurrences, future probability, and magnitude and severity. The criteria for each of these impact designations are provided in Table 3-6. Colorado Natural Hazards Mitigation Plan 3 12

13 Table 3 6: Hazard Analysis Summary Category Descriptions Geographic Location Statewide Regional Local Previous Occurrences Perennial Seasonal Sporadic Future Probability Expected Likely Occasional Unlikely Magnitude/Severity Catastrophic Extensive Moderate Minimal Occurring across the state and largely indiscriminate of geologic or environmental considerations. Occurring predominately in sub areas of the state based on location and associated exposure to atmospheric, geologic, or other environmental conditions. Occurring within an impact confined to a small or geographically isolated area or relating to, or characteristic of a particular place. Active throughout the year on multiple occasions or lasting indefinitely. Occurring at specific times of the year or dependent on a particular seasons and associated atmospheric conditions. Occurring at irregular intervals; having no pattern or order in time; appearing singly or at widely scattered localities; dependant on aggravating or cascading circumstances. Annual event or assumed to occur at least one per year. Occurs in the range of about once every 10 years. Occurs only every 11 to 100 years. Considered an once in a lifetime event. Occurs greater than every 100 years. Mass fatality and casualty; significant population displacement or other quality of life impacts; damage to property, facilities, infrastructure resulting in loss of use or accessibility; service disruption; need for outside resources. Isolated deaths and injuries; quality of life impacts; major or long term impact to property, facilities, infrastructure, or critical services. Minimal death or injury; limited quality of life impacts; minor or short term impact on property, facilities, infrastructure, or critical services. No deaths and few injuries; minor quality of life impacts; little or no impact on property, facilities, infrastructure, or critical services. Colorado Natural Hazards Mitigation Plan 3 13

14 Definition and Characteristics General definitions and characteristics of hazards are included in the HIRA to provide a common understanding as to what the natural event is and why it is of enough concern to make it a hazard in Colorado. These definitions and characteristics were reviewed and updated or enhanced for some hazards. Geographic Location Natural hazards occurring in Colorado range from statewide to regional with some specifically associated with the geologic attributes of a localized area. The geographic extent for each hazard is presented in text and supported by tables or maps where available and appropriate. In many cases, the statewide geographic extent of hazards has been refined in this plan update. Previous Occurrences Every county in the state has experienced the adverse affects of natural hazards. Descriptions of previous occurrences, or known hazard incidents, are included to help frame the extent of the hazards impact on areas of Colorado. In some cases, detailed accounts are provided for significant historic hazard events. Occurrences for every hazard were reviewed and updated from the For some hazards detailed historic events and associated deaths, injuries, and total damage by county were included for the first time. The Spatial Hazard Events and Losses Database for the United States (SHELDUS) was used in addition to other sources. SHELDUS based data equally distributes injuries, deaths, and property damages across counties for multi-jurisdictional events. This data was rounded to whole number by county for the purposes of this plan. Future Probability The likelihood of a hazard occurring again looks toward past frequency to assist in determining the probability of future occurrence. For some hazards, the future probability of events is further supported by assumptions that favorable environmental conditions resulting in a hazard event will continue to develop or persist. Magnitude and Severity Assessment of severity in expressed in terms of consequence of impacts such as injuries and fatalities, damage to personal property, infrastructure, state or local critical assets, and the environment, negative affects on the economy, and the degree and extent with which the hazard affects the ability to provide essential services. Magnitude and severity is further considered in the vulnerability assessment and consequence analysis. Natural hazards are grouped into the following areas for the purpose of developing profiles: atmosphere, geologic, and other hazards. This grouping allows for a more Colorado Natural Hazards Mitigation Plan 3 14

15 logical and cohesive approach toward analysis and understanding than if the hazards were presentation in alphabetical order. Atmospheric Hazards Geologic Hazards Other Hazards Drought Extreme Heat Floods Hailstorms Lightning Precipitation Thunderstorms Tornadoes Windstorms Winter Weather Avalanche Earthquake Erosion and Deposition Expansive Soils Landslides, Mud/Debris Flows, Rockfalls Subsidence Wildfire Grasshopper Infestation Colorado Natural Hazards Mitigation Plan 3 15

16 Atmospheric Hazards Drought Extreme Heat Floods Hailstorms Lightning Precipitation Thunderstorms Tornadoes Windstorms Winter Weather Colorado Natural Hazards Mitigation Plan 3 16

17 Drought Aside from a few instances, information provided in this section is summarized from the Colorado Drought Mitigation and Response Plan (2010), a detailed hazard specific annex to the Colorado Pre-Disaster Mitigation Plan that was updated and enhanced as part of this planning effort. Otherwise, the information originated and was updated from the 2007 PDM plan. For additional details, please refer to the drought specific plan. Hazard Profile Summary Consideration Impact Description Geographic Location Statewide Mountains and plains both experience drought. Changes geographically from year to year and decade to decade. Drought in one area of the state may affect other regions. Previous Occurrences Sporadically Drought may occur at any time of the year and be short or long term in development, duration, and ending. Future Probability Likely Atmospheric conditions resulting in severe drought conditions are expected to occur as frequently in the future as in the past. The Colorado Drought Mitigation and Response Plan also notes that, Short duration drought as defined by the three month Standardized Precipitation Index (SPI) occur somewhere in Colorado in nearly nine out of every ten years. Magnitude/Severity Extensive Limited property damage that does not threaten structural integrity; deaths (3 4 per year); and injuries; little or no impact critical services or facilities. May result in significant economic and water resource impacts. Definition Drought may be defined several different ways depending upon the source or impact. The following definitions of drought are considered for this plan: Meteorological drought a period of below-average precipitation. Agricultural drought a period of inadequate water supply to meet the needs of the state s crops and other agricultural operations such as livestock. Hydrological drought deficiencies in surface and subsurface water supplies. Generally measured as streamflow, snowpack, and as lake, reservoir, and groundwater levels. Socioeconomic drought occurs when drought impacts health, well-being, and quality of life, or when a drought starts to have an adverse economic impact on a region. Colorado Natural Hazards Mitigation Plan 3 17

18 Characteristics With its semiarid conditions, drought is a natural part of the Colorado climate. Due to natural variations in climate and precipitation, single season droughts over some portion of the state occur nearly every year. Hydrologic conditions constituting a drought for water users in one location may not constitute a drought for water users elsewhere, or for water users that have a different water supply. Individual water suppliers may use criteria, such as rainfall/runoff, amount of water in storage, or expected supply from a water wholesaler, to define their water supply conditions. The drought issue is further influenced by water rights specific to a state or region. Water is a commodity regulated under a variety of legal doctrines. Geographic Location No portion of the State of Colorado is immune from drought conditions. The effects of drought vary based on where in the state it occurs, when it happens, and how long the drought persists. Droughts that occur in the mountainous regions of the state during winter months may have great affects on the ski and tourism industry. However, drought in one area of the state may also impact other regions. Lack of winter snowfall in the mountains can eventually lead to agricultural impacts on the eastern plains due to decreased streamflows. Reduced reservoir storage from decreased runoff in the mountains can lead to voluntary, or in severe cases, mandatory municipal and/or industrial water usage restrictions on the Front Range. Droughts that occur in populated areas may increase the threat of wildfire in the wildland urban interface areas. Previous Occurrences Several times since the late 1800s Colorado has experienced widespread, severe drought. The most dramatic occurred in the 1930s and 1950s when many states, Colorado included, were affected for several years at a time. Table 3-7 below shows six multi-year droughts experienced in Colorado since Colorado Natural Hazards Mitigation Plan 3 18

19 Table 3 7: Historical Dry and Wet Periods in Colorado Date Dry Wet Duration (years) * * 6 Source: Colorado Drought Mitigation and Response Plan (2010); McKee, et al. *modified for this Plan in 2010 based on input from the CCC Table 3-8 includes a list of years where significant drought conditions occurred somewhere in Colorado since As noted below, in some cases short-lived periods of drought occurred during overall periods of wetter than normal conditions on a statewide basis: Table 3 8: Colorado s Significant Drought Conditions Since Year 1900 The 1930 s Drought The 1950s Drought The 1977 Drought The Dust Bowl drought severely affected much of the United States during the 1930s. During the 1950s, the Great Plains and the southwestern U.S. withstood a five year drought, and in three of these years, drought conditions stretched coast to coast. The 1950s drought was characterized by both decreased rainfall and excessively high temperatures. The area from the Texas panhandle to central and eastern Colorado, western Kansas, and central Nebraska experienced severe drought conditions. During 1976 and 1977, the state experienced record low streamflows at two thirds of the major stream gages, records that held until the 2002 drought Drought Short lived, beginning in the fall of 1980 and lasting until the summer of Drought Significant impacts reported included an increase in wildfires statewide, loss to the winter wheat crops, difficulties with livestock feeding, and impacts to the State s fisheries Drought July 29, the Governor issued an Executive Order proclaiming a Drought Disaster Emergency Declaration for fifteen counties. Colorado Natural Hazards Mitigation Plan 3 19

20 2002 Drought On a statewide basis, 2002 was the most intense single year of drought in Colorado s history. This was an extremely dry year embedded in a longer dry period ( ). These conditions were rated exceptional by the U.S. Drought Monitor and were the most severe drought experienced in the region since the Dust Bowl. Based on studies of tree rings and archaeological evidence from aboriginal cultures, the 2002 drought was the most severe in the recorded history of the state. Source: Colorado Drought Mitigation and Response Plan (2010); NCDC, Colorado Climate Center, Mckee and Doesken, Tronstad and Feuz Case History During 1976 and 1977, the State experienced record-low stream flows at two-thirds of the major stream gages, records that held until the 2002 drought. In addition, the Colorado ski industry estimated revenue losses at $78.6 million; agriculture producers incurred higher crop production costs due to water supply shortages; and numerous municipalities were forced to impose water use restrictions on their customers. The state s agriculture producers and municipalities received over $110 million in federal drought aid as a result of the drought. The drought of 2002 is considered the most intense drought on record. Statewide snowpack was at or near all time lows. What made 2002 so unusual was that all of the State was dry at the same time. By all accounts, soil moisture was nearly depleted in the upper one-meter of the soil profile over broad areas of Colorado by late August was clearly the driest year in over 100 years of record based on streamflow. Future Probability Historical analysis of precipitation shows that drought is a frequent occurrence in Colorado. Short duration drought as defined by the three-month Standardized Precipitation Index (SPI) occur somewhere in Colorado in nearly nine out of every ten years. However, severe, widespread multiyear droughts are much less common. According to the 2004 Drought Water Supply Assessment, there have been six recorded drought incidents totaling 36 dry years which impacted the State of Colorado since 1893, or a span of 111 years. ( = 111 years). This formula evaluates that the probability of a drought occurring in any given year is 32.4 percent. Figure 3-1, from the National Drought Mitigation Center, indicates that most of Colorado has experienced severe or extreme drought between 15 and 19.9 percent of the time from Future analyses of probability and magnitude and severity will improve with the development of improved tools as part of the 2010 update. Colorado Natural Hazards Mitigation Plan 3 20

21 Figure 3 1: Palmer Drought Severity Index, 1895 to 1995 Magnitude and Severity Drought impacts are wide-reaching and may come in different forms, such as economic, environmental, and/or societal. Drought is one of the few hazards with the potential to directly or indirectly impact the entire population of the State, be it from water restrictions, higher water and food prices, reduced air or water quality, or restricted access to recreational areas. The most significant impacts associated with drought in Colorado are those related to water intensive activities such as agriculture, wildfire protection, municipal usage, commerce, tourism, recreation, and wildlife protection. Since 2003, there have been 16 USDA Secretarial Disasters declared for various counties in Colorado. These declarations provided financial assistance to what can be devastating losses in crop production and associated agricultural crop or rangeland revenues. Tourism in Colorado is strengthened by protected areas that are owned and managed by the State. Drought impacts to these assets translate to declines in tourism and related industries. Furthermore, decreased revenues for state agencies resulting from drought can reduce management budgets, which can have a detrimental impact on lands and wildlife. Colorado Natural Hazards Mitigation Plan 3 21

22 Droughts may also result in a reduction of electric power generation and water quality deterioration. Drought conditions can also cause soil to compact, decreasing its ability to absorb water, making an area more susceptible to flash flooding and erosion. A drought may also increase the speed at which dead and fallen trees dry out and become more potent fuel sources for wildfires. Drought may also weaken trees in areas already affected by mountain pine beetle infestations, causing more extensive damage to trees and increasing wildfire risk, at least temporarily. Further analysis of magnitude and severity is provided by sectors and subsectors in the attached drought mitigation plan. The sectors are as follows: Agriculture, Energy, Environment, Municipal and Industrial, Recreation, and Socioeconomic. The recreation, energy, and agricultural sectors were further broken out for more detailed analyses. Recreation was broken into rafting, boating, golf, wildlife viewing, skiing, and hunting, camping, and fishing. The energy sector was broken into mining and power while agriculture has the sub-sectors of green industries, livestock, and crops. Sources Colorado Drought Mitigation and Response Plan (2010) The Drought of 2002 in Colorado, McKee and Doesken Impacts of the 2002 drought on western ranches and public land policies, Western Economics Forum, Tronstad and Feuz (2002) Colorado Climate Center (CCC) Colorado Water Resources Research Institute National Weather Service (NWS), National Climatic Data Center (NCDC) Colorado Natural Hazards Mitigation Plan 3 22

23 Extreme Heat Hazard Profile Summary Consideration Impact Description Geographic Location Regional Areas of the state with highest temperatures are concentrated along the front range and eastern plains, the Grand Valley, and extreme southwest. Previous Occurrences Seasonal Every few years in high temperature prone areas of the state, average temperatures will be at extreme highs for one to three weeks. Future Probability Occasional Each year, any number of days with extreme heat exceeds normal high temperatures around the state. High temperature events of prolonged duration are not frequent. Magnitude/Severity Moderate Limited property damage that does not threaten structural integrity; minor injuries; little or no impact critical services or facilities. Definition Extreme heat conditions are defined by summertime weather that is substantially hotter and/or more humid than average for a location at that time of year. This definition for extreme heat may be refined with considerations such as summertime temperatures that hover 10 degrees or more above the average high temperature for the region and last for several week. The Heat Index (HI) or the "Apparent Temperature" is an accurate measure of how hot it actually feels when the Relative Humidity (RH) is added to the actual air temperature. The heat index may be used to help determine when an extreme heat event is occurring. Characteristics North American summers are typically hot with heat waves occurring in one or more parts of the United States each year. East of the Rockies, extreme heat tends to combine both high temperature and high humidity; although some of the worst heat waves have been catastrophically dry. Over the last 30 years in the United States, excessive heat accounts for more reported deaths annually than hurricanes, floods, tornadoes, and lightning combined. The extreme heat hazard in Colorado is often underestimated because other natural hazards occur more frequently and its effects can vary based on region and vulnerable population within the State. Colorado Natural Hazards Mitigation Plan 3 23

24 Figure 3 2: Weather Fatalities in the United States, 1977 to 2006 Source: National Weather Service Humid or muggy conditions, which add to the discomfort of high temperatures, occur when a "dome" of high atmospheric pressure traps hazy, damp air near the ground. Excessively dry and hot conditions can provoke dust storms and low visibility. Heat alert procedures from the National Weather Service (NWS) are based mainly on Heat Index Values. The Heat Index, sometimes referred to as the apparent temperature and given in degrees Fahrenheit, is a measure of how hot it really feels when relative humidity is factored with the actual air temperature. The NWS heat index chart is presented in Figure 3-3. Colorado Natural Hazards Mitigation Plan 3 24

25 Figure 3 3: NOAA s National Weather Service Heat Index Since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15 degrees F. Geographic Location Average temperatures across Colorado vary as extremely as, and in relation to, the changes in elevation. The eastern plains and Western Slope of the state experience average temperatures in July between 70 and 80 degrees. At higher elevations, these temperatures tend to be lower with highs reaching into the 60s. Previous Occurrence During 2008, Denver's 87 year-old record for the number of consecutive days above 90 degrees F was broken. The new record of twenty-four consecutive days surpassed the previous record by almost a week. On August 1st, it reached 104 degrees, breaking a record set in 1938 and on August 2nd, it reached 103 degrees, breaking a record set in Table 3-9 shows Denver s historic count of 90 degrees or higher days since The average number of 90 degree days per in Denver is 33. In 2000, the number of days was nearly double the average with 61 days of 90 degree temperatures or higher. Colorado Natural Hazards Mitigation Plan 3 25

26 Table 3 9: Denver s 90 Degree Days Year Total Days Source: NWS Extreme high temperatures recorded in Colorado counties are shown in Table Although viewing record highs does not necessarily equate to prolonged extreme heat events, the table provides an indication of potential temperature extremes across the state. Table 3 10: Summary of Extreme High Temperatures in Colorado by County: County Temperature (F)* County Temperature (F)* Adams 105 La Plata 102 Alamosa 96 Lake 86 Arapahoe 108 Larimer 102 Archuleta 99 Las Animas 103 Baca 111 Lincoln NA Bent 112 Logan 110 Boulder 106 Mesa 108 Chaffee 95 Mineral 97 Cheyenne 108 Moffat 104 Clear Creek 84 Montezuma 101 Conejos 95 Montrose 110 Costilla 97 Morgan 107 Crowley NA Otero 110 Custer 94 Ouray 91 Delta 106 Park 95 Denver 103 Phillips 109 Dolores 99 Pitkin NA Douglas 99 Prowers 109 Eagle 100 Pueblo 108 El Paso 99 Rio Blanco 108 Elbert 100 Rio Grande 93 Colorado Natural Hazards Mitigation Plan 3 26

27 County Temperature (F)* County Temperature (F)* Fremont 105 Routt 98 Garfield 104 Saguache NA Gilpin NA San Juan 88 Grand 94 San Miguel 97 Gunnison 98 Sedgwick 109 Hinsdale 98 Summit 98 Huerfano 101 Teller NA Jackson 96 Washington NA Jefferson 103 Weld NA Kiowa 110 Yuma NA Kit Carson 107 *As Recorded At A Natural Resources Conservation Service (U.S.D.A.) Temperature And Precipitation Stations (TAPS) Note: Not All Data Covers A 30 Year Period. Source: The average number of days in Colorado with temperatures greater than or equal to 90 degrees and 100 degrees F are shown in Figure 3-4. Portions of Baca County in the southeastern corner of the state may have 80 or more days of 90 degrees F or greater temperatures a year. Most of the county may experience fifteen to eighteen days of 100 degrees F or greater. Figure 3 4: Number of Days with Temperatures Greater than or Equal to 90 and 100 Degrees 100 Degrees 90 Degrees Source: High Plains Regional Climate Center Future Probability Since the record hot year of 1998, six of the last ten years ( ) have had annual average temperatures that fall in the hottest 10 percent of all years on record for the Colorado Natural Hazards Mitigation Plan 3 27

28 United States. This example supports a shift towards a warmer climate with an increase in extreme high temperatures and a reduction in extreme low temperatures. These types of changes have been apparent in the western half of North America. Figure 3-5 shows that since before 1900, Colorado much like the rest of the county is in a warming cycle. Statewide, the average temperature over the last 110 years is about 45 degrees F. The trend line for state temperatures during this time has increased from 44 to 46 degrees. Figure 3 5: Colorado Annual Average Temperature, 1895 to 2010 Source: National Weather Service Colorado Natural Hazards Mitigation Plan 3 28

29 Magnitude and Severity Health Impacts The July 1995 heat wave killed 522 people in Chicago alone. Research by the Centers for Disease Control (CDC) found that on a national average 384 people were killed by excessive heat each year during the period 1979 to This is significantly higher than the numbers reported in the National Weather Service's Summary of Natural Hazards Deaths. This is due in part to the research methodology of local NWS offices relying on published accounts of events rather than death certificates. Attributing excessive heat as a cause or contributing factor in mortality has varied considerably across jurisdictions. This has led to speculation that the actual, as opposed to reported, death toll is much higher. For example, one study suggests that the actual death toll of the 1980 heat wave may be 5,000, not the official number of 1,700. Other studies indicate that diagnosis of heat-related deaths have been regularly underestimated by 22 percent to 100 percent. The population of Colorado has become less sensitive to the impacts of excessive heat events over the course of the past 30 to 40 years despite rising urban temperatures. This is a trend common to most major cities across the United States as result of the increased availability and use of air conditioning and the implementation of social programs aimed at caring for high-risk individuals. Colorado Natural Hazards Mitigation Plan 3 29

30 Figure 3 5: Heat related mortality trends across the U.S. Figure 7. Annual heat related mortality rates (excess deaths per standard million population). Each histogram bar indicates a different decade (from left to right, 1970s, 1980s, 1990s). (Source: Davis et al., 2003b). (Source: SPPI 2008) For nearly all cities, including Denver, the number of heat-related deaths is declining (the bars are get smaller) as shown in Figure 3-5. This indicates that there has been a decrease in heat-related deaths over time meaning that the population has become better adapted to heat waves. This adaptation is most likely a result of improvements in medical technology, access to air-conditioned homes, cars, and offices, increased public awareness of potentially dangerous weather situations, and proactive responses of municipalities during extreme weather events. Colorado Natural Hazards Mitigation Plan 3 30

31 Regardless of any trends indicating heat-related deaths are declining, extreme heat events remain a danger. Specific high-risk groups typically experience a disproportionate number of health impacts from extreme heat conditions. The populations that have physical, social, and economic factors and the specific actions that make them at high risk include: Older persons (age > 65) Infants (age < 1) The homeless The poor People who are socially isolated People with mobility restrictions or mental impairments People taking certain medications (e.g., for high blood pressure, depression, insomnia) People engaged in vigorous outdoor exercise or work or those under the influence of drugs or alcohol. Each year children die from hyperthermia as a result of being left in parked vehicles. Hyperthermia is an acute condition that occurs when the body absorbs more heat than it can dissipate. Hyperthermia can occur even on a mild day. Studies have shown that the temperature inside a parked vehicle can rapidly rise to a dangerous level for children, adults and pets. Leaving the windows slightly open does not significantly decrease the heating rate. The effects can be more severe on children because their bodies warm at a faster rate than adults. Those at greatest risk of death in heat waves are the urban-dwelling elderly without access to an air-conditioned environment for at least part of the day. Thus the issues of prevention and mitigation combine issues of the aging and of public health. As shown in Figure 3-6, between 1999 and 2003, heat related deaths of persons 65 and older were significantly higher than other age groups. Colorado Natural Hazards Mitigation Plan 3 31

32 Figure 3 6: Number of Heat Related Deaths, by Sex and Age Group in the United States, 1999 to 2003 Source: United States Center for Disease Control Transportation Impacts There are several impacts on transportation documented in case studies. Aircraft lose lift at high temperatures and major airports have been closed due to periods of extreme heat that made aircraft operations unsafe. Highways and roads are damaged by excessive heat as asphalt roads soften and concrete roads have been known to "explode" lifting 3 to 4 foot pieces of concrete. During the 1980 heat wave, hundreds of miles of highways buckled. Stress is placed on automobile cooling systems, diesel trucks and railroad locomotives which lead to an increase in mechanical failures. Train rails develop sun kinks and distort. Refrigerated goods experience a significant greater rate of spoilage due to extreme heat. Agriculture Various sectors of the agriculture community are affected by extreme heat. Livestock, such as rabbits, poultry, pigs, and cows are severely impacted by heat waves. Millions of birds have been lost during heat waves and milk production and cattle reproduction also Colorado Natural Hazards Mitigation Plan 3 32

33 decreases during heat waves. High temperatures at the wrong time inhibits a crop yields and wheat, rice, maize, potato, and soybean crop yields can all be significantly reduced by extreme high temperatures at key development stages. Energy The electric transmission system is impacted when power lines sag in high temperatures and can lead to power outages. The combination of extreme heat and the added demand for electricity to run air conditioning causes transmission line temperatures to rise. The demand for electric power during heat waves is well documented. In 1980, consumers paid $1.3 billion more for electric power during the summer than the previous year. The demand for electricity, 5.5 percent above normal, outstripped the supply, causing electric companies to have rolling black outs. Water Resources The demand for water increases during periods of hot weather. In extreme heat waves, water is used to cool bridges and other metal structures susceptible to heat failure. This causes a reduced water supply and pressure in many areas. This may also contribute to fire suppression problems for both urban and rural fire departments. The rise in water temperature during heat waves contributes to the degradation of water quality and negatively impacts fish populations. It can also lead to the death of many other organisms in the water ecosystem. High temperatures are also linked to rampant algae growth that may result in fish kills in rivers and lakes. Sources Cooperative Institute for Research in the Atmosphere (CIRA) Science and Public Policy Institute (SPPI), 2008 United States Global Change Research Program, 2008 National Weather Service (NWS) National Oceanic and Atmospheric Administration (NOAA) Federal Emergency Management Agency (FEMA) United States Centers for Disease Control (CDC) Colorado Natural Hazards Mitigation Plan 3 33

34 Floods Information provided in this section is primarily summarized and paraphrased from the Flood Hazard Mitigation Plan for Colorado (2010). The flood specific plan is a detailed hazard specific annex to the State Plan that was updated and enhanced as part of this planning effort. For a more in-depth discussion on risk, please refer to the flood specific plan. Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Flood prone areas have been identified in 268 of 270 cities and towns and in all of the 64 counties in Colorado. Previous Occurrences Seasonal Notable flood events from 1864 to 2010 include dozens of events. These event totals included significant deaths (363) and damages ($5.8 Million). Future Probability Likely In addition to annual minor flooding events, Colorado experiences major floods every 5 years on average. Magnitude/Severity Extensive Major floods may induce property damage that threatens structural integrity, result deaths and injuries, and impact critical services, facilities, and infrastructure. Between 20 and 30 large magnitude floods (in terms of peak discharge) occur somewhere in Colorado every year with varying impact depending on location. Definition A flood is a general and temporary condition of partial or complete inundation of normally dry land areas from: (1) the overflow of stream banks, (2) the unusual and rapid accumulation of runoff of surface waters from any source, or (3) mudflows or the sudden collapse of shoreline land. Flooding results when the flow of water is greater than the normal carrying capacity of the stream channel or accumulates faster than surface absorbency allows. The floodplain is land adjoining the channel of a river, stream, lake or other watercourse or water body that is susceptible to flooding. Characteristics The causes of floods relate directly to the accumulation of water from precipitation, rapid snowmelt, or the failure of human made structures, such as dams or levees. Floods caused by precipitation are further classified as coming from: Colorado Natural Hazards Mitigation Plan 3 34

35 Rain in a general storm system Rain in a localized intense thunderstorm Melting snow Rain on melting snow Ice jams Geographic Location Flood prone areas have been identified in 268 of 270 cities and towns and in all of the 64 counties in Colorado. HAZUS 100-year floodplains for Colorado are shown in Figure 3-7 and highlight the statewide potential for flooding. However, not all problem reaches may be identified as indicated by the potential lack of floodplains in portions of southern Grand County and northern Mesa County. Figure 3 7: HAZUS MH 100 year Floodplains in Colorado In addition to floodplains, the location of Colorado s most significant dams allows for point of origin analysis related to downstream impacts of release. The Colorado Division of Water Resources runs the Dam Safety Program. Of the non-federal dams in Colorado, Colorado Natural Hazards Mitigation Plan 3 35

36 approximately 677 are classified as dams that, in the event of a failure, would be expected to cause loss of life and/or significant property damage within the flood plain areas below the dams. These dams are referred to as Class I High or Class II Significant and are described further in Table Table 3 11: Classification of Dams Classification Class I High Class II Significant Class III Low Class IV No Public Hazard Loss of human life is expected. Description Significant damage is expected, but not loss of human life. Significant damage refers to structural damage where humans live, work, or recreate or public or private facilities exclusive of unpaved roads and picnic areas. Damage refers to making the structures uninhabitable or inoperable. Loss of human life and damage to structures and public facilities not expected. No loss of human life is expected and damage will only occur to the dam owner s property in the event of dam failure. Source: Colorado Division of Water Resources Figure 3-8 shows the general location of Colorado s class I and Class II dams while the accompanying Table 3-12 provides a detailed breakdown of the number of dams by county. Dams are concentrated along the central and northern Front Range, particularly in Larimer and Boulder Counties, and along the Colorado River in Mesa County. Figure 3 8: Colorado Class I and Class II Dam Locations Colorado Natural Hazards Mitigation Plan 3 36

37 Table 3 12: Class I and Class II Dams in Colorado by County County Class I Class II County Class I Class II Adams 8 12 Kit Carson 1 0 Alamosa 0 0 La Plata 8 6 Arapahoe 8 4 Lake 3 2 Archuleta 2 8 Larimer Baca 1 0 Las Animas 6 1 Bent 2 0 Lincoln 1 2 Boulder Logan 3 0 Broomfield 3 1 Mesa Chaffee 2 2 Mineral 5 6 Cheyenne 0 0 Moffat 1 3 Clear Creek 8 5 Montezuma 8 7 Conejos 2 3 Montrose 9 1 Costilla 3 1 Morgan 0 6 Crowley 0 2 Otero 0 7 Custer 0 1 Ouray 1 0 Delta Park 5 3 Denver 7 3 Phillips 0 0 Dolores 1 2 Pitkin 2 7 Douglas 2 6 Prowers 0 1 Eagle 8 5 Pueblo 3 4 El Paso Rio Blanco 3 3 Elbert 0 0 Rio Grande 1 1 Fremont 3 3 Routt 8 5 Garfield 6 11 Saguache 0 1 Gilpin 1 0 San Juan 0 0 Grand 7 12 San Miguel 5 0 Gunnison 6 6 Sedgwick 3 0 Hinsdale 3 4 Summit 5 2 Huerfano 5 3 Teller 4 10 Jackson 0 4 Washington 1 0 Jefferson Weld Kiowa 0 2 Yuma 1 7 Source: Colorado Division Of Water Resources 2001 Previous Occurrence Between 20 and 30 large magnitude floods occur somewhere in Colorado every year. The earliest known floods are reported to have occurred in 1826 in the Arkansas River and Republican River basins. The most notable flood events in Colorado from 1864 to 2010 are presented in the notable flood event table below. As indicated in Table 3-13, the Colorado Natural Hazards Mitigation Plan 3 37

38 greatest loss of life occurred during the Big Thompson flood event of The most damaging flood in Colorado occurred in June 1965 on the South Platte River when over $2.7 billion in damages (2010 dollars) was sustained in the Denver metro area. Table 3 13: Notable Flood Events in Colorado: Year Location Deaths Damages (2010$) 1864 Cherry Creek (Denver) 0 $7,365, Bear Creek (Morrison) 27 $8,418, San Juan River (by Pagosa Springs) 2 $7,365, Cherry Creek (Denver) 2 $164,152, Arkansas River (Pueblo) 78 $1,039,634, Monument Creek (Col. Springs) 18 $71,553, Kiowa Creek near Kiowa 9 $21,045, South Platte River Basin NA $11,364, Purgatorie River (Trinidad) 2 $49,456, * Denver, Jefferson, Arapahoe Counties 1957 Western Colorado 0 $24,202, * South Platte River (Denver) 8 $2,735,879, Arkansas River Basin 16 $280,953, * South Platte River Basin 0 $29,463, * Southwest Colorado 0 $17,888, * South Platte River (Denver) 10 $531,392, * Big Thompson River (Larimer) 144 $115,748, * Fall River (Estes Park) 3 $67,344, North Central Counties 10 $35,776, * West & Northwest Counties 2 $64,187, Western Slope 0 $2,841, Western Slope & South Platte 21 $71,553, * Fort Collins & 13 East Counties 6 $231,497, * Col. Springs, 12 East Counties 0 $136,793, Beaver, Brush Hollow, Eightmile Creeks (Fremont) 0 $2 million 2006 Horse Creek, West Creek (Douglas) 0 $13.3 million 2006 Vallecito Creek (La Plata) 0 $1.0 million 2007 Chalk Creek Canyon (Chaffee) 0 $1.0 million 2007 Chalk Creek Canyon mudflows (Chaffee) 0 $2.0 million 2009 Six Mile Creek (Fremont) 0 $321k Totals 363 $5,787,438, Sources: Colorado Flood Hazard Mitigation Plan 2007, NCDC, SHELDUS NOAA NWS ( *Denotes federal disaster declaration event Colorado Natural Hazards Mitigation Plan 3 38

39 Case History The Big Thompson Canyon flood disaster of July 31, 1976 was a result of an intense thunderstorm cell that stalled over the Big Thompson River Basin and dropped up to 10 inches of rain in a few hours (equivalent to a year s annual precipitation). The massive amount of rain, combined with the canyon s thin soil, sparse vegetation and steep rock walls, transformed the normally two-foot-deep river into a wall of water 19 feet high. The immense flash flood roared through the canyon where thousands of people were recreating. Two law enforcement officers attempted to warn people of the impending danger, but the sheer volume and velocity of the flood waters were overwhelming. Many people lost their lives trying to outrun the deluge, not knowing that they should climb to higher ground for safety. Within a couple hours, the Big Thompson Canyon flood killed 145 people (including six who were never found), destroyed 418 houses and damaged another 138, destroyed 152 businesses and caused more than $40 million in damages. The Big Thompson flood remains the deadliest natural disaster in Colorado to date. On July 24 to 28, 1997, the City of Fort Collins and most of eastern Colorado received soaking and/or drenching rains, adding to soil moisture in some locations. Several inches of new rain were reported just west and northwest of Fort Collins totally saturating the ground, producing major flooding in Laporte, and setting the stage for the evening flood event. On the evening of July 28, 1997, intense rains began around 6:30 p.m. in the foothills west of Fort Collins. Winds from the east and southeast continued to pump moisture into the storm system throughout the evening. Rainfall intensity increased and reached a maximum between 8:30 p.m. and 10:00 p.m. before ending abruptly. Significant property damage occurred, including to Colorado State University facilities. Future Probability Flooding will continue to occur in Colorado. As mentioned previously, between 20 and 30 large magnitude floods (in terms of peak discharge) occur somewhere in Colorado every year. In addition, between 1965 and 1999, Colorado experienced nine major flood disasters as indicated in Table 3-14: Table 3 14: Colorado Major Flood Disasters Year Flood Extent Front Range communities Front Range communities 1970 Southwestern Colorado Front Range communities Front Range communities 1982 Larimer County (dam failure) Western Slope counties Eastern Colorado counties Southeastern Colorado counties Colorado Natural Hazards Mitigation Plan 3 39

40 Magnitude and Severity Statewide flood events come in all levels of intensity, but Colorado does have a history of tragic flood events. In 1965, damages in Denver were evaluated at over $2.7 billion (in 2010 dollars) due to a South Platte River flood. The greatest loss of life occurred during the Big Thompson flood of 1976 with 145 deaths. There are countless examples of flood events in Colorado causing negative impacts on people, property, and the environment. The attached flood mitigation plan provides greater detail on the statewide impacts of flooding and the more notable historical flood events. In Colorado there are over 17,600 flood insurance policies in effect. Since January 1, 1978, insurance companies have paid close to 2,000 claims to Colorado policy holders; $8 million in payments have been received. According to the FEMA Disaster Report for Colorado, there are 40 repetitive loss properties, which are defined as residences incurring at least $1,000 in flood damage two or more times over a 10-year period. See the attached flood mitigation plan for more complete information on Colorado s repetitive loss properties. Sources Colorado Division of Water Resources Colorado Department of Transportation (2007) Spatial Hazard Events and Losses Database for the United States (SHELDUS) National Weather Service, National Climatic Data Center (NCDC) Federal Emergency Management Agency (FEMA) Colorado Natural Hazards Mitigation Plan 3 40

41 Hailstorms Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Concentrated along the Front Range and east central to northeast Colorado, although most counties have recorded hail events. Previous Occurrences Seasonal Storms occur many times a year, often with widespread limited damage. Over last sixty years, an annual average of 142 statewide events is reported. Seasonal typically late spring through early fall. Future Probability Expected Hailstorms resulting in property or agricultural damage are an annual occurrence. Atmospheric convection activity producing conditions prone to hail are expected to occur in the future as in the past. Magnitude/Severity Moderate Although large events may result in high aggregate insured losses, typically there is limited property damage and structural integrity is not threatened; minor injuries; little or no impact critical services or facilities. Definition Hail is described as showery precipitation in the form of irregular pellets or balls of ice. The National Weather Service uses the following standard hail size descriptions: Table 3 15: Hail Size Chart Severity Description Hail Diameter Size Non Severe Hail Does not typically cause damage and does not warrant severe thunderstorm warning from NWS. Severe Hail Research has shown that damage occurs after hail reaches around 1 in diameter and larger. Hail of this size will trigger a severe thunderstorm warning from NWS. Pea 1/4" Plain M&M 1/2" Penny 3/4" Nickel 7/8" Quarter 1" (severe) Half Dollar 1 1/4" Walnut/Ping Pong Ball 1 1/2" Golf Ball 1 3/4" Hen Egg/Lime 2" Tennis Ball 2 1/2" Baseball 2 3/4" Teacup/Large Apple 3" Grapefruit 4" Softball 4 1/2" Computer CD DVD 4 3/4" 5" Source: NWS Colorado Natural Hazards Mitigation Plan 3 41

42 Characteristics In North America, hail is most common in the area where Colorado, Nebraska, and Wyoming meet, known as "Hail Alley." Hail in this region occurs between the months of March and October during the afternoon and evening hours. Colorado s damaging hail season is typically from mid-april to mid-august. Formation of hail occurs inside a thunderstorm where there are strong updrafts of warm air and downdrafts of cold air. If a water droplet is picked up by the updrafts it can be carried high enough to where temperatures fall below 32 degrees where it freezes. As the frozen droplet begins to fall as it is carried by cold downdrafts, it may thaw as it moves into warmer air toward the bottom of the thunderstorm. The half-frozen droplet may get picked up again by another updraft where it is carried back into very cold air and refreezing it. With each trip above and below the freezing level the frozen droplet adds another layer of ice. The frozen droplet eventually falls to the ground as hail which can reach speeds up to 120 MPH. Geographic Location Colorado s Front Range and Eastern Plains are located in the heart of "Hail Alley," receiving the highest frequency of large hail in the United States. Figure 3-9 shows that the further east in Colorado, the more hail days typically occur. Although it appears that the state is generally on the edge of the hail-prone area of the country, areas in Colorado range from 1 to 10 hail days per year. An area in northern Colorado and southeastern Wyoming endures hailstorms 8+ days each year. Figure 3 9: Annual Hail Days, 1995 to 1999 Source: National Severe Storms Laboratory, NOAA Colorado Natural Hazards Mitigation Plan 3 42

43 Previous Occurrences There is a high occurrence of hail events on the eastern, compared to the western side of Colorado as shown in Figure Since 1950, ninety-three percent (93%) of all reported hail events occurred in the eastern part of the state, with most of the events concentrated in the northeast. Figure 3 10: Reported Hail Events by County, 1950 to 2010 There are three (3) counties with over 500 reported hail events between 1950 and El Paso County has the highest number of hail events with 884, followed by Weld County with 600 and Yuma County with 578. Although these counties account for twenty-four percent (24%) of total reported events combined, they only account for one percent (1%) of total reported damage. Case History On the night of July 20th, 2009, a strong storm hit the northwest suburbs of Denver, dumping as much as an inch of rain in less than an hour and hail that was one-inch in Colorado Natural Hazards Mitigation Plan 3 43

44 diameter. The storm damaged numerous cars, windows and roofs. A greenhouse containing plants worth more than $250,000 was destroyed. Straight-line winds of 80 miles per hour uprooted mature trees and damaged roofs. The storm also left 50,000 residents without power. The Rocky Mountain Insurance Information Association lists the July 20th storm as the costliest hazard event since 1990 in terms of insured losses in the Rocky Mountain Region. To date, RMIIA has identified $767.6 million in damages from the storm. The July 20, 2009, storm was not the only event to cause significant damage in Severe weather including hail and tornadoes from June 6 to 15 of 2009 resulted in $353.3 million in insured losses. Another storm in the Pueblo Area on July 29th caused more than $200 million in damages. Overall, 2009 was the costliest severe weather season, with a total of $1.4 billion in insured losses. Future Probability Hailstorms resulting in property or agricultural damage are an annual occurrence. Three or four times a year, hailstorms with at least $25 million in insured damage occur. Atmospheric convection activity producing conditions prone to hail are expected to occur in similar frequency and extent in the future as in the past. Magnitude and Severity Since 1990, the majority of the costliest hazard events in Colorado are hailstorms, the greatest of which are shown in Table While hailstorms do not threaten lives to the same degree as a flood or a tornado, they do pose significant risks to roofs, windows, cars, crops and other forms of property. Table 3 16: Colorado s Most Costly Hail Storms Date Location Cost When Occurred (Millions) July 20, 2009 Denver Metro $767.6 July 11, 1990 Denver Metro $625.0 June 6 15, 2009 Denver Metro $353.3 June 13 14, 1984 Denver Metro $276.7 July 29, 2009 Pueblo $232.8 October 1, 1994 Denver Metro $225.0 May 22, 2008 Windsor $193.5 June 8 9, 2004 Denver Metro $146.5 August 11, 1997 Denver Metro $128.0 May 22, 1996 Denver Metro $122.0 Source: Rocky Mountain Insurance Information Association, 2010 *2009 estimated cost calculations based on the Consumer Price Index Colorado Natural Hazards Mitigation Plan 3 44

45 Vehicles, roofs of buildings and homes, and landscaping are the property most commonly damaged by hail. A significant amount of damage inflicted by hail is to crops. Even small hail can cause significant damage to crops in a short period of time. In Colorado s case, counties with the highest population densities are generally located along the Front Range. In particular, the higher density counties include the Denver region along with Larimer County (City of Fort Collins), El Paso County (City of Colorado Springs), and Pueblo County (City of Pueblo). The total number of high density counties including the Denver Metro area is twelve (12). All other fifty-two counties (52) in the state are considered lower density. Table 3-17 provides a comparison of hail events and property damage between higher and lower population density counties in Colorado. Higher density counties, while only representing 36.6 percent of all reported hail events between 1950 and 2010, account for 93 percent of reported statewide damage. This percentage equates to the 12 high density counties accounting for $1.2 billion of the $1.3 billion in total reported statewide damage since Table 3 17: Hail Damage by County Population Density, 1950 to 2010 County by Density Number of Events Property Damage Crop Damage Total Damage Total Higher Density Counties 3,130 $1,154,147,000 $36,917,000 $1,191,064,000 Metro Denver* 1,574 $963,953,000 $81,000 $964,034,000 Larimer 350 $2,560,000 $1,836,000 $4,396,000 El Paso 884 $35,112,000 $0 $35,112,000 Pueblo 322 $152,522,000 $35,000,000 $187,522,000 Lower Density Counties 5,425 $32,342,040 $57,598,500 $89,940,540 Total 8,555 $1,186,489,040 $94,515,500 $1,281,004,540 Percent Higher Density Counties 36.6% 97.3% 39.1% 93.0% Metro Denver 18.4% 81.2% 0.1% 75.3% Larimer 4.1% 0.2% 1.9% 0.3% El Paso 10.3% 3.0% 0.0% 2.7% Pueblo 3.8% 12.9% 37.0% 14.6% Lower Density Counties 63.4% 2.7% 60.9% 7.0% Source: National Climate Data Center, 2010, Colorado State Demographers Office, 2009 *Includes the counties of Adams, Arapahoe, Boulder, Broomfield, Clear Creek, Denver, Gilpin, and Jefferson. Jefferson County, located on the west side of the Denver Metro area, experienced the highest amount of property damage in the state since This county has $350 million in report damages representing over twenty-seven percent (27%) of the statewide total. Table 3-18 shows a breakout of deaths, injuries, and property damage by county. Colorado Natural Hazards Mitigation Plan 3 45

46 Table 3 18: Hailstorm Events, Deaths, Injuries, and Damage in Colorado by County, 1950 to 2010 County Number of Events Deaths Injuries Property Damage Crop Damage Total Damage Adams $204,001,000 $50,000 $204,051,000 Alamosa $500,000 $500,000 $1,000,000 Arapahoe $249,426,000 $31,000 $249,457,000 Archuleta $0 $0 $0 Baca $150,000 $0 $150,000 Bent $6,201,000 $3,100,000 $9,301,000 Boulder $1,005,000 $0 $1,005,000 Broomfield $0 $0 $0 Chaffee $1,000 $0 $1,000 Cheyenne $851,000 $3,000 $854,000 Clear Creek $0 $0 $0 Conejos $0 $0 $0 Costilla $455,000 $250,000 $705,000 Crowley $0 $0 $0 Custer $1,000 $0 $1,000 Delta $0 $100,000 $100,000 Denver $156,500,000 $0 $156,500,000 Dolores 2 $5,000 $30,000 $35,000 Douglas $3,000,000 $0 $3,000,000 Eagle $0 $0 $0 El Paso $35,112,000 $0 $35,112,000 Elbert $10,000 $0 $10,000 Fremont $6,000 $0 $6,000 Garfield $0 $0 $0 Gilpin $0 $0 $0 Grand $5,000 $0 $5,000 Gunnison $0 $0 $0 Hinsdale $0 $0 $0 Huerfano $30,000 $0 $30,000 Jackson $0 $0 $0 Jefferson $350,021,000 $0 $350,021,000 Kiowa $0 $500,000 $500,000 Kit Carson $908,000 $0 $908,000 La Plata $11,000 $500 $11,500 Lake $0 $0 $0 Larimer $2,560,000 $1,836,000 $4,396,000 Las Animas $0 $0 $0 Lincoln $11,000 $110,000 $121,000 Logan $21,000 $100,000 $121,000 Colorado Natural Hazards Mitigation Plan 3 46

47 County Number of Events Deaths Injuries Property Damage Crop Damage Total Damage Mesa $750,000 $500,000 $1,250,000 Mineral $0 $0 $0 Moffat $10,000 $45,000 $55,000 Montezuma $1,139,000 $125,000 $1,264,000 Montrose $0 $0 $0 Morgan $2,200,000 $2,500,000 $4,700,000 Otero $70,000 $0 $70,000 Ouray $0 $0 $0 Park $40 $0 $40 Phillips $20,000 $9,500,000 $9,520,000 Pitkin $0 $0 $0 Prowers $5,060,000 $500,000 $5,560,000 Pueblo $152,522,000 $35,000,000 $187,522,000 Rio Blanco $1,035,000 $0 $1,035,000 Rio Grande $5,000 $5,000 Routt $55,000 $100,000 $155,000 Saguache $5,000 $250,000 $255,000 San Juan $0 $0 $0 San Miguel $0 $0 $0 Sedgwick $0 $0 $0 Summit $0 $0 $0 Teller $5,000 $0 $5,000 Washington $30,000 $1,200,000 $1,230,000 Weld $10,906,000 $30,130,000 $41,036,000 Yuma $1,886,000 $8,055,000 $9,941,000 Total 8, $1,186,489,040 $94,515,500 $1,281,004,540 Source: National Climatic Data Center, NOAA, 2010 Sources The Denver Post Colorado State Demography Office National Weather Service (NWS) National Climatic Data Center (NCDC) National Severe Storms Laboratory Rocky Mountain Insurance Information Association (RMIIA) Colorado Natural Hazards Mitigation Plan 3 47

48 Lightning Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Concentrated along the front range and higher elevations. All counties experience severe weather with lightning. Previous Occurrences Perennial State averages 529,000 cloud to ground lightning flashes per year. Reported deaths and/or injuries occur on a regular basis. Future Probability Expected State averages 529,000 cloud to ground lightning flashes per year. Atmospheric convection activity producing conditions prone to lightning are expected to occur as in the past. Magnitude/Severity Extensive Limited property damage that does not threaten structural integrity; deaths (1 2 per year) and injuries (6 7 per year); little or no impact to critical services or facilities aside from occasional short term power outages. Definition Lightning is a luminous, electrical discharge in the atmosphere caused by the electriccharge separation of precipitation particles within a cumulonimbus (thunderstorm) cloud. Thunder is the resulting sound wave caused by the sudden expansion of air heated by a lightning discharge. Characteristics Lightning can occur anywhere there is a thunderstorm. Lightning is one of the most underrated severe weather hazards, yet ranks as one of the top weather killers in the United States. Lightning strikes in America kill about 58 people and injure hundreds of others each year. Colorado ranked 18th compared to other states in the total number of cloud-to-ground lightning flashes recorded between 1996 and During this period, the state experienced over 529,000 annual average flashes. Experiencing 5.1 flashes per square mile, Colorado ranked 31st in the nation for cloud-to-ground lightning flash density from 1996 to Florida holds the top spot in flash density with 25.3 flashes per square mile, while Washington has the lowest at 0.3 per square mile. (Source: Vaisala Inc., Tucson Operations) Colorado Natural Hazards Mitigation Plan 3 48

49 The average number of lightning flashes for any given day for each month is shown in the Table In any given day in July or August, over 4,000 lightning flashes are expected to occur in Colorado. Table 3 19: Average Lightning Flashes in Colorado by Day/Month Month Number of Flashes Per Day January 1 February 4 March 39 April 225 May 1,203 June 2,621 July 4,035 August 4,215 September 1,457 October 261 November 11 December 1 Source: NWS Geographic Location Figure 3-11 shows cloud to ground lightning activity over the state of Colorado for a sixteen year (16) period from 1989 to 2005, excluding Areas shown in red indicate the highest density of annual cloud to ground lighting strikes while areas in blue show the lowest. Lightning strikes are associated with thunderstorm activity, and the areas showing the greatest number of lightning strikes have geographic characteristics that lend toward greater atmospheric convection. The areas in the map below showing red and yellow are at the intersection of the mountains and plains and along the major east-to-west ridge called the Palmer Divide. Colorado Natural Hazards Mitigation Plan 3 49

50 Figure 3 11: Colorado Annual Lightning Flash Density, 1989 to 2005 Source: National Weather Service In areas of Colorado with the most lightning activity, more than 3.5 cloud to ground lightning flashes can be expected to hit the ground in a 1 square kilometer area. Converting this to square miles, one can expect about nine (9) cloud to ground flashes to hit the ground per square mile. The least amount of lightning activity occurs in the San Luis Valley, the central mountain regions, and the Upper Arkansas River valley. The primary hot spot for lightning in Colorado is the greater Pikes Peak region, including Colorado Springs. Another hot spot is in the Trinidad area (Raton Mesa). The reason why so much lightning occurs in these regions is due to a combination of topography, low level wind flow regime, and low level atmospheric moisture. Colorado Natural Hazards Mitigation Plan 3 50

51 Previous Occurrence The average amount of cloud to ground lightning for the state of Colorado is 529,000 flashes per year. This number was measured over a 9 year time period from 1996 through Figure 3-12 shows the general distribution of these flashes across the state. Figure 3 12: Annual Number of Cloud to Ground Lightning Flashes by County Source: Colorado Lightning Resource Center, NWS Pueblo Previous occurrences and the geographical extent of lightning are somewhat synonymous, showing a high history of lighting strikes along the Front Range. Lightning events resulting in injuries or deaths provides a look at the risk to people across Colorado. Figure 3-13 shows combined reported lightning injuries and deaths by county over the last 60 years. Larimer, Boulder, Jefferson, Arapahoe, and El Paso Counties have over 21 lightning deaths and/or injuries since These are followed by Weld, Adams, Douglas, Grand, Eagle, and Huerfano Counties with 11 to 20 reported deaths and/or injuries during this time period. Colorado Natural Hazards Mitigation Plan 3 51

52 Figure 3 13: Lightning Injuries and Deaths by County, 1950 to 2010 Table 3-20 shows the number of reported deaths injuries respectively by County from 1950 to El Paso County has the most reported lighting deaths with 10, followed closely by Jefferson with 8 and Larimer with 7. El Paso County also stands out as the location with the most lightning injuries with 58 persons. Arapahoe, Boulder, Denver, Grand, and Jefferson were the only other counties with 20 or greater injuries during this timeframe. Colorado Natural Hazards Mitigation Plan 3 52

53 Table 3 20: Lightning Deaths and Injuries by County, 1950 to 2010 County Deaths Injuries County Deaths Injuries Adams 4 13 Kit Carson 0 2 Alamosa 0 1 La Plata 1 5 Arapahoe 3 24 Lake 0 3 Archuleta 0 3 Larimer 7 53 Baca 0 0 Las Animas 0 0 Bent 0 0 Lincoln 0 1 Boulder 4 28 Logan 0 1 Broomfield 0 0 Mesa 1 3 Chaffee 2 4 Mineral 1 0 Cheyenne 0 0 Moffat 1 0 Clear Creek 0 7 Montezuma 1 3 Conejos 0 0 Montrose 3 1 Costilla 0 0 Morgan 1 4 Crowley 0 0 Otero 2 0 Custer 1 0 Ouray 1 0 Delta 0 0 Park 5 4 Denver 3 22 Phillips 0 0 Dolores 0 0 Pitkin 3 4 Douglas 1 12 Prowers 1 3 Eagle 2 9 Pueblo 1 7 El Paso Rio Blanco 1 5 Elbert 1 0 Rio Grande 3 1 Fremont 1 0 Routt 3 4 Garfield 2 0 Saguache 1 1 Gilpin 0 0 San Juan 1 5 Grand 0 20 San Miguel 0 3 Gunnison 0 10 Sedgwick 0 0 Hinsdale 0 0 Summit 0 0 Huerfano 0 11 Teller 4 4 Jackson 1 0 Washington 0 0 Jefferson 8 36 Weld 1 11 Kiowa 0 0 Yuma 0 0 Total Source: NCDC Case History During the early evening of 24 July 2008, two graduate students were struck by lightning on the Colorado State University (CSU) campus in Fort Collins, Colorado. According to CSU news media, they were struck in the Sherwood Forest area of the campus which is a heavily treed area just south of the Warner College of Natural Resources Building. One Colorado Natural Hazards Mitigation Plan 3 53

54 student was pronounced dead shortly after the incident. The other student survived for 2 days before succumbing to his injuries. On September 2, 2007, a 21 year old male was killed by lightning while inside a tent which was located in the foothills 8 miles southwest of Colorado Springs, Colorado. Three other people were also in the tent when the flash occurred, but they received only minor injuries. An autopsy report indicated the man who was killed was lying down on the ground inside the tent at the time of the flash. The autopsy report indicated the electrical current entered through his elbow on which he was leaning on at the time, traveled through his torso, and exited his buttocks. The other three occupants in the tent were standing at the time of the flash. At approximately 5:30 pm on July 19, 2006, a 17 year old was struck and killed by lightning at Cavanaugh Field which is located in Woodland Park, Colorado. He was playing soccer with friends when he was struck. None of the other players were injured by this flash. 0n June 19, 2004, nineteen golfers were struck by lightning near the town of Kremmling, Colorado. They were participating in the Kremmling Cliff Classic Golf Tournament which was located on a bluff a mile or two north of town. This "golf tournament" consisted of hitting golf balls off the edge of a cliff at targets in the valley below. Of the 19 golfers who were affected by the flashes, 4 were taken via helicopter to a hospital in Denver. Reports from the Grand County dispatch center indicated the first 911 call regarding this lightning incident was received at 2:46 pm. Eyewitnesses and victims to the event indicated 2 flashes actually hit the bluff where the 19 golfers were injured. Future Probability Figure 3-14 depicts the counties in which humans are most at risk from personal injury from lightning, excluding fire risks. Calculations were based on the following values assigned to total deaths and injuries and number of lightning flashes per county: Deaths and Injuries Value Lightning Flashes Value The value of deaths/injuries was added to the value assigned to the lightning flashes. The resulting values range from 0 to 6. Values from 5 to 6 represent areas determined to be at high risk. Values from 3 to 4 represent areas with moderate risk and values less than 3 represent areas with low risk. Colorado Natural Hazards Mitigation Plan 3 54

55 Figure 3 14: Lightning Risk by County Table 3-21 represents the lighting risk calculations by county with the results serving as the base for the previous map. El Paso County was the only jurisdiction to obtain a ranking of 6, based on achieving both the highest number of deaths and injuries and highest average annual number of lightning flashes. Colorado Natural Hazards Mitigation Plan 3 55

56 Table 3 21: Colorado by Counties Ranked by Lightning Risk, 1950 to 2010 County Death and Injury Death and Injury Value Average Annual Flashes Average Annual Flashes Combined Risk Ranking El Paso , Weld , Larimer , Elbert , Lincoln , Rio Blanco , Pueblo , Douglas , Jefferson , Arapahoe , Las Animas , Mesa , Park , Moffat , Routt , Montezuma , Garfield , Fremont , La Plata , Saguache , Huerfano , Adams , Grand , Boulder , Denver , Washington , Yuma , Kit Carson 2 1 9, Montrose 4 1 8, Logan 1 1 8, Gunnison , Archuleta 3 1 7, Morgan 5 1 7, San Miguel 3 1 7, Prowers 4 1 7, Otero 2 1 5, Teller 8 1 5, Jackson 1 1 5, Eagle , Colorado Natural Hazards Mitigation Plan 3 56

57 County Death and Injury Death and Injury Value Average Annual Flashes Average Annual Flashes Combined Risk Ranking Baca 0 0 8, Cheyenne 0 0 7, Kiowa 0 0 7, Bent 0 0 6, Dolores 0 0 6, Custer 1 1 4, Mineral 1 1 3, Pitkin 7 1 3, Clear Creek 7 1 3, Chaffee 6 1 2, Ouray 1 1 2, Rio Grande 4 1 1, San Juan 6 1 1, Lake Alamosa Broomfield 0 0 NA 0 0 Conejos 0 0 4, Hinsdale 0 0 3, Costilla 0 0 3, Crowley 0 0 3, Delta 0 0 3, Phillips 0 0 2, Sedgwick 0 0 2, Summit 0 0 1, Gilpin 0 0 1, Total ,600 Source: NCDC, CDEM Colorado Natural Hazards Mitigation Plan 3 57

58 Magnitude and Severity Death and injury is the greatest risk lightning poses to people. Table 3-22 shows the top five (5) states for lighting deaths. Between 1995 and 2009, Colorado ranked fourth in the nation for lighting deaths with 44. Florida stood out with a total of 115 lighting deaths, followed by Iowa and Texas with 57 and 44 respectively. Ohio rounds out the top five with 28 deaths. Table 3 22: Lightning Deaths by State, 1995 to 2009 State Total Florida 115 Iowa 57 Texas 46 Colorado 44 Ohio 28 Source: NWS In a study in the Denver, Colorado area, it was found that one (1) out of every 52 lightning flash results in an insurance claim; while nationwide the ratio is 1 to 57. (NWS) With Colorado averaging 529,000 flashes per year and an average of one insurance claim per 52 strikes, the state is averaging over 10,000 insurance claims per year. In addition to direct damages from lightning, wildfire ignition is of great concern. Lightning strike density was included in the Colorado Wildfire Risk Assessment and potential losses for wildfire can be viewed in the wildfire section. Deaths and injuries to livestock and other animals, thousands of forest and brush fires, as well as millions of dollars in damage to buildings, communications systems, power lines, and electrical systems are also the result of lightning. Total property damage reported from lightning strikes in Colorado is $19.4 million over the last 50 years, as shown in Table Based on the number of events reported, damages average to $31,433 per lightning event. Significant crop damage is also reported from lightning, totaling about $2.0 million during this timeframe. Colorado Natural Hazards Mitigation Plan 3 58

59 Table 3 23: Lightning Events, Deaths, Injuries, and Damage in Colorado by County, 1960 to 2008 County Number of Events Property Damage Crop Damage Total Damage Adams 24 $469,435 $16,181 $485,616 Alamosa 6 $44,793 $26 $44,819 Arapahoe 33 $904,819 $25,514 $930,333 Archuleta 10 $143,411 $0 $143,411 Baca 12 $3,670 $36,458 $40,128 Bent 12 $4,170 $36,458 $40,628 Boulder 45 $992,390 $15,651 $1,008,041 Chaffee 9 $102,793 $2,026 $104,819 Cheyenne 11 $3,682 $37,083 $40,765 Clear Creek 7 $7,394 $26 $7,420 Conejos 3 $161 $0 $161 Costilla 2 $161 $0 $161 Crowley 10 $3,982 $265,625 $269,607 Custer 3 $2,632 $26 $2,658 Delta 6 $36,661 $0 $36,661 Denver 51 $1,308,525 $18,125 $1,326,650 Dolores 4 $2,724 $15,625 $18,349 Douglas 28 $2,784,212 $15,625 $2,799,837 Eagle 8 $512,556 $26 $512,582 El Paso 67 $6,558,582 $37,292 $6,595,874 Elbert 10 $253,329 $23,958 $277,287 Fremont 10 $262,793 $26 $262,819 Garfield 8 $115,879 $250 $116,129 Gilpin 6 $14,894 $26 $14,920 Grand 9 $7,556 $26 $7,582 Gunnison 7 $41,661 $0 $41,661 Hinsdale 2 $161 $0 $161 Huerfano 10 $43,526 $26 $43,552 Jackson 5 $7,556 $26 $7,582 Jefferson 42 $1,497,140 $42,318 $1,539,458 Kiowa 11 $3,670 $36,458 $40,128 Kit Carson 16 $505,104 $545,417 $1,050,521 La Plata 7 $14,724 $15,625 $30,349 Lake 8 $17,793 $26 $17,819 Larimer 41 $122,390 $15,651 $138,041 Las Animas 6 $1,957 $15,625 $17,582 Lincoln 16 $5,104 $45,417 $50,521 Logan 20 $8,094 $62,639 $70,733 Mesa 17 $89,161 $250 $89,411 Mineral 3 $161 $0 $161 Colorado Natural Hazards Mitigation Plan 3 59

60 County Number of Events Property Damage Crop Damage Total Damage Moffat 5 $31,379 $0 $31,379 Montezuma 13 $284,224 $15,625 $299,849 Montrose 9 $51,661 $5,000 $56,661 Morgan 15 $27,935 $40,947 $68,882 Otero 11 $19,207 $265,625 $284,832 Ouray 4 $1,161 $0 $1,161 Park 12 $12,793 $30,026 $42,819 Phillips 17 $7,210 $54,306 $61,516 Pitkin 9 $4,793 $26 $4,819 Prowers 13 $8,670 $36,458 $45,128 Pueblo 24 $691,756 $32,318 $724,074 Rio Blanco 5 $629 $0 $629 Rio Grande 4 $161 $0 $161 Routt 9 $44,924 $0 $44,924 Saguache 7 $3,293 $26 $3,319 San Juan 5 $1,724 $15,625 $17,349 San Miguel 7 $6,724 $15,625 $22,349 Sedgwick 15 $5,044 $37,639 $42,683 Summit 10 $7,556 $26 $7,582 Teller 11 $2,845 $0 $2,845 Washington 17 $30,044 $39,439 $69,483 Weld 39 $1,225,935 $32,681 $1,258,616 Yuma 18 $16,877 $45,972 $62,849 Total 884 $19,385,950 $1,992,900 $21,378,850 Source: SHELDUS Sources Vaisala Inc Colorado Division of Emergency Management (CDEM) Spatial Hazard Events and Losses Database for the United States (SHELDUS) National Weather Service (NWS) National Climatic Data Center (NCDC) Colorado Natural Hazards Mitigation Plan 3 60

61 Precipitation Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Higher snowfall amounts in the mountains, lower overall rain and snow totals for plains and select southern and western regions. Overall geographic variability. Previous Occurrences Perennial Regular occurrences throughout the year in the form of rain, snow, hail, sleet, etc. Future Probability Expected Atmospheric activity producing conditions prone to precipitation are expected to occur as in the past. Magnitude/Severity Extensive Major or long term property damage that threatens structural stability, isolated deaths and/or injuries, potential impact to critical services or facilities. Precursor to hazards such as flood, land movement, drought, winter storm. Dictates statewide water supply. Definition Precipitation is the term used for any form of water, such as rain, snow, sleet, or hail that falls to the earth's surface. Characteristics Precipitation is an ordinary natural event in most areas of the United States. However, excessive rainfall or rapid snowmelt may produce a flash flooding hazard, which can quickly endanger both life and property. Flooding may result from the accumulation of heavy rainfall over an extended period of time or unseasonably high temperatures that can trigger increased snow melt and runoff. The possibility for flash flooding is particularly hazardous in the valleys of mountainous regions where rapid runoff can occur from the steep slopes. Urban areas are also at risk for local flooding, as hard, impermeable surfaces like concrete do not allow rainwater to be absorbed into the ground. (NOAA) Generally, the eastern United States receives more moisture than the western United States, as shown in Figure Colorado s statewide average annual precipitation is 16 to 17 inches but ranges from only 7 inches in the middle of the San Luis Valley in south central Colorado to over 60 inches in a few mountain locations. (Colorado Climate Center) Colorado Natural Hazards Mitigation Plan 3 61

62 Figure 3 15: Annual Average Precipitation in the United States Geographic Location As a result of the State's distance from major sources of moisture (the Pacific Ocean and the Gulf of Mexico) precipitation is generally light in the lower elevations. Prevailing air currents reach Colorado from westerly directions. Eastward-moving storms originating in the Pacific Ocean lose much of their moisture falling as rain or snow on the mountaintops and westward-facing slopes. Eastern slope areas receive relatively small amounts of precipitation from these storms, particularly in mid winter. During the fall and winter months, strong northerly winds may come in contact with moist air from the south. The interaction of these air masses can cause a heavy fall of snow and a blizzard, which is the most severe of all weather conditions of the high plains. Cold air is frequently too shallow to cross the mountains from the western portion of the State to the east. This means that when the plains are in the grip of a very severe storm, the weather in the mountains and western valleys may be mild. Figure 3-16 shows Colorado s average annual precipitation for a 29 year period from 1961 to Areas with the highest precipitation relate to high elevations, especially in Colorado Natural Hazards Mitigation Plan 3 62

63 the north central mountains. The San Luis Valley and areas of the Western Slope are the driest areas in the state, receiving less than 10 inches of annual precipitation. Figure 3 16: Average Annual Precipitation in Colorado Source: Oregon Climate Service Warm, moist air from the south moves into Colorado infrequently, but most often in the spring, summer and early autumn. As this air is carried northward and westward to higher elevations, the heaviest and most general rainfalls (and sometimes wet snows) occur over the eastern portions of the State from April through early September. For southern and western Colorado, the intrusions of moist air are most common from mid July into September and associated with wind patterns commonly referred to as the Southwest Monsoon. Frequent showers and thunderstorms continue well into the summer as a result of this pattern. Eastern Plains An important feature of the precipitation in the plains is the seasonal cycle. A very large proportion of the precipitation (70 to 80 percent of the annual total) falls during the growing season from April through September. Cool seasonal precipitation is important for soil moisture recharge, and midwinter precipitation is light and infrequent. From early March through early June, periodic widespread storms bring moisture that helps crops and grasslands. Summer precipitation over the plains comes largely from thunderstorm activity and can be extremely heavy. Localized rains in excess of 4" sometimes fall in Colorado Natural Hazards Mitigation Plan 3 63

64 just a few hours which may result in local flooding. In late May 1935 nearly two feet of rain fell along the Republican River in eastern Colorado causing one of the worst floods in state history. June flash floods in 1965 were also devastating. The weather station at Holly in southeast Colorado measured 18.81" of rainfall in that extraordinarily wet month. It is more common, however, to be too dry. Annual average precipitation ranges from less than 12 inches in the Arkansas Valley between Pueblo and Las Animas to almost 18 inches in extreme northeastern and southeastern corners of the state. Many years are drier than average, and some years receive only half or less the long-term average. Mountains Precipitation patterns are largely controlled by mountain ranges and elevation. Precipitation increases with elevation both in winter and summer but the elevation effect is greatest in mid winter when winds at mountain top level are typically strongest. High peaks and mountain ranges generally receive the majority of their precipitation during the winter months. Snow accumulates without melting in both shaded and level areas at elevations above about 8,000 feet. When it melts in the spring, this snow is the primary source of water for much of the state s population and provides water for extensive irrigation. Considerable effort is made every year to measure the accumulating snowpack so that water providers and resource managers can plan ahead for the coming summer. Most of the mountain snow melts during May and June when rivers reach their peak for the year. Western Colorado Precipitation west of the Continental Divide is more evenly distributed throughout the year than in the eastern plains. For most of western Colorado, the greatest monthly precipitation occurs in the winter months, while June is the driest month. Near the Utah border, late summer and early autumn can be the wettest time of year. While precipitation only averages from 8 to 14 inches in these western valleys, localized flood-producing storms are still possible. Occasionally, moisture from decayed Pacific hurricanes has fueled widespread heavy rains. Extensive flooding occurred in October 1970 following one of these storm systems. (Colorado Climate Center) Colorado Natural Hazards Mitigation Plan 3 64

65 Previous Occurrence Precipitation occurs naturally throughout the year with the potential of affecting any part of the state at any given time. Table 3-24 provides a summary of precipitation extremes for areas of Colorado. Table 3 24: Colorado Precipitation Extremes Precipitation Measure Amount/Duration Date Location Record Maximum Annual Precipitation Ruby Record Minimum Annual Precipitation Buena Vista Record Maximum 24 hour Precipitation Jun 1965 Holly Highest Average Annual Precipitation Wolf Creek Pass Lowest Average Annual Precipitation 7.05 Center Consecutive Days Measurable 45 days Nov 83 Jan 84 Berthoud Pass Consecutive Days with no Measurable 156 days Oct 36 Mar 37 Haswell Source: Western Region Climate Center There are significant resources in Colorado that monitor occurrences of statewide precipitation by watersheds, mountain ranges, and other natural and jurisdictional boundaries. These include the Natural Resources Conservation Service, Colorado Water Conservation Board, the National Climate Data Center, Colorado Climate Center, and the National Weather Service, to name a few. The National Climate Data Center keeps precipitation reports for Colorado under the categories of precipitation, snow and ice, and hail. The reported events under precipitation are all described as heavy rain events and provided the best descriptions of localized impacts from this hazard. Snow and ice reports were not listed by jurisdiction and generally reported snow depth and climatic conditions rather than impact, thus were not included in this profile. Hailstorm reports are included within the hailstorms hazard profile. Reported heavy rain events for 2009 are shown in Table The reports are provided as an example showing that rain precipitation events occur statewide. These events occur with varying degrees of impact and the summer months tend to produce the heaviest rains. Colorado Natural Hazards Mitigation Plan 3 65

66 Table 3 25: Colorado Heavy Rain Reports, 2009 Location Date Description Castle Rock 6/1/2009 Loma 6/2/2009 Greeley 6/9/2009 Grand Junction 6/18/2009 Fruitvale 6/26/2009 Delta 6/26/2009 Ridgway 6/26/2009 Grand Junction 6/26/2009 Palisade 6/26/2009 Telluride 7/26/2009 Deckers 8/5/2009 Westcreek 8/5/2009 Heavy rain caused significant trail damage in Castlewood Canyon. A couple of wooden walkways over the creek were also washed out. A severe thunderstorm over Phillips County produced very heavy rain, which resulted in flash flooding near Holyoke. Heavy rain and minor flooding was also observed in Castlewood Canyon, east of Castle Rock. Heavy rainfall resulted in minor street and road flooding. A NWS employee in the impacted area measured 0.75 of an inch of rain within 35 minutes. Heavy rain fell north of Fruita. Severe thunderstorms produced heavy rain, large hail and one weak tornado in Weld County. The storm dumped 1 to 2 inches of rain in the Greeley, Evans, Johnstown and Milliken in about 30 minutes causing some street flooding. Large hail, up to quarter size, was reported in Washington, Weld and Lincoln Counties. Heavy rainfall in some areas of Grand Junction resulted in minor street flooding on North Avenue, in Clifton, and in the Redlands. A spotter in the Redlands area of Grand Junction reported 0.56 of an inch of rain within 15 minutes. EPISODE NARRATIVE: Heavy rain fell in some areas of Grand Junction. Street flooding was encountered by persons traveling near Orchard Avenue and 29.5 Road. Heavy rainfall caused minor flooding in some areas of western Colorado. Heavy rainfall caused street flooding in the southern part of the town of Delta, including the area around 12th and Main Street. Heavy rainfall caused minor flooding in some areas of western Colorado. Heavy rainfall totaling 0.82 of an inch fell within about an hour resulting in minor street flooding. Heavy rainfall caused minor flooding in areas of western Colorado. Heavy rainfall resulted in minor flooding in many areas within the Grand Junction metropolitan area. Street flooding occurred along North Avenue between 4th and 7th Streets, along 7th Street between North Avenue and Orchard Avenue, and on Patterson Road between 12th and 15th Streets. Flood waters also seeped into the Doubletree Hotel where some water damage occurred. Heavy rainfall caused minor flooding in some areas of western Colorado. Heavy rainfall resulted in a mudslide next to I 70 at Exit 42. The heavy rainfall also caused the fall of several large boulders onto the westbound lanes of I 70 near mile marker 43. The boulders, which weighed up to a thousand pounds, closed the westbound lanes of I 70 for about an hour until they were all removed. Heavy rainfall caused minor flooding in some areas of western Colorado. Heavy rainfall caused two new culverts to fill up with debris under a bridge spanning Pack Creek and caused water to flow over the top of the new US Forest Service bridge. The bridge was damaged and a gorge was formed on the other side of the bridge. Heavy rainfall resulted in minor flooding along a popular trail. Heavy rain triggered a mudslide along State Highway 126 at 6 Mile Hill. Heavy rain and hail in the Hayman burn area triggered several mudslides and caused some minor flooding. Heavy rain caused several mudslides along State Highway 67 near Oxyoke, north of Deckers. Five washout areas were observed. Heavy rain and hail in the Hayman burn area triggered several mudslides and caused some minor flooding. Source: National Climatic Data Center Colorado Natural Hazards Mitigation Plan 3 66

67 Future Probability Many of the resources in Colorado that monitor statewide precipitation by watersheds, mountain ranges, and other natural and jurisdictional boundaries, also provide precipitation forecasts and outlooks. Looking at these sources on a regular basis (monthly, quarterly, or annually) may provide indications of the short-term probability of expected precipitation in general terms of low, average, or high. Figure 3-17 represents a predictive example from the National Weather Service s Climate Prediction Center showing normal to below precipitation for areas of Colorado from January through March of Figure 3 17: Three Month Precipitation Probability Outlook, September 2010 Source: National Weather Service Colorado Natural Hazards Mitigation Plan 3 67

68 Figure 3-18 shows average precipitation compared to average for the last 125 years. Between 1895 and 2009, Colorado s annual average precipitation was about 16 inches. The overall annual precipitation trend during this period reflects a negative 0.07 inches per decade. This chart also shows that during this timeframe, Colorado tends to experience swings of wet and dry seasons rather than precipitation amounts staying close to average. Figure 3 18: Colorado Annual Precipitation History, 1895 to 2010 Source: National Climatic Data Center La Niña and El Niño are the popular terms for alternating cold and warm phases of ocean temperatures in the eastern and central Pacific Ocean off the coast of South America. Ocean temperatures are of concern because they may have significant impact on Colorado s precipitation. El Niño and La Nina El Niño typically energizes the southern jet stream leaving the northern states relatively dry and mild while the southern states often experience above normal precipitation with normal to slightly below normal temperatures. Conversely, La Niña winters typically Colorado Natural Hazards Mitigation Plan 3 68

69 produce a more active northern jet stream with colder and wetter conditions in northern states. Colorado is located on the line between these northern and southern patterns, as shown in Figure 3-19, where some winters are cold and snowy while others may be drier, but close to normal or above normal in temperature. Figure 3 19: El Nino and La Nina Air Flows Source: National Weather Service Figure 3-20 provides insight into the historical cycle of La Nina and El Nina. Information provided in the chart may be useful in suggesting the future probability of wet or dry years. Figure 3 20: Southern Oscillation Index Source: National Weather Service Eastern Colorado requires gulf moisture to energize snow storms. El Niño develops in response to rising Pacific Ocean temperatures. Additional moisture is provided by the Colorado Natural Hazards Mitigation Plan 3 69

70 warmer water, but most of this moisture falls out over the Rocky Mountains west of the Continental Divide. The active southern jet stream provides the disturbances necessary for producing snow east of the Rockies, but the moisture for big snow storms still has to come from the Gulf of Mexico. The track and speed of these storm systems determine how much gulf moisture and for how what period of time it affects the eastern parts of Colorado. Upslope easterly/northeasterly winds are important since surface wind imports gulf moisture from the east and pushes it up against the Front Range. The storm track can also drop too far south to provide Colorado with necessary upslope to generate snowfall thus drier than normal conditions may develop even in an El Niño year. Magnitude and Severity Precipitation in the form of both rainfall and snowfall is fundamental to irrigation for agriculture, the generation of hydropower, a variety of recreational opportunities on lakes and ski slopes, and as a key source of freshwater for human consumption. Colorado is a headwater state. All rivers in Colorado rise within its borders and flow outward, with the exception of the Green River, which flows diagonally across the extreme northwestern corner of the State. Four of the Nation's major rivers have their source in Colorado: the Colorado, the Rio Grande, the Arkansas, and the Platte. (Colorado Climate Center) More specifically, melting snow packs during the late spring and summer months supply a significant percent of the water supply for the western United States. Dams impound this melt water for domestic, hydroelectric, industrial, and agricultural use throughout the year. Water managers monitor how seasonal or annual changes in climate (e.g. drought, El Niño-Southern Oscillation) affect the accumulation and melting rate of snow. Variables including previous precipitation, watershed characteristics, land use, and other climatic variables such as wind and temperature determine the potential impact of precipitation. Heavy snowfall may result in roof collapse, ice accumulation may impact power infrastructure, heavy rains may leak into buildings and cause damage, and hail can cause significant damage to personal property such as cars and homes in addition to causing death and injury. Ice, hail, sleet/freezing rain frequently cause poor and unsafe driving conditions. See specific hazard profiles for additional information. Sources Skyview Weather Oregon Climate Service Colorado Climate Center (CCC) National Weather Service (NWS) National Weather Service, Climate Prediction Center National Climatic Data Center (NCDC) National Oceanic and Atmospheric Administration (NOAA) Western Region Climate Center Colorado Natural Hazards Mitigation Plan 3 70

71 Thunderstorms Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Higher number of severe thunderstorms along Front Range and all of eastern Colorado. Thunderstorms occur statewide with varying elevation based characteristics. Previous Occurrences Seasonal Regular occurrences from spring through late summer or early fall. Most severe storms typically occur midsummer. Future Probability Expected Atmospheric activity producing conditions prone to thunderstorms are expected to occur as in the past. Magnitude/Severity Extensive Major or long term property damage that threatens structural stability, isolated deaths and/or injuries, potential impact to critical services or facilities. Precursor to hazards such as flood, wind, hail, tornadoes, and lightning. Definition Thunderstorms are a transient storm of lightning and thunder, usually with rain and gusty winds. Characteristics Thunderstorm and lightning events occur when unstable, warm air rises swiftly, moisture forms clouds and rain, and air currents are lifted upward due to mountains or colliding weather fronts (cold and warm). The National Weather Service (NWS) classifies a thunderstorm as severe if wind speeds reach 58 mph or greater, a tornado is produced or surface hail of 0.75 or greater is dropped. The National Weather Service estimates that more than 100,000 thunderstorms occur each year in the continental United States; fortunately only about 10 percent are classified as severe. Thunderstorms may produce deadly and damaging tornadoes, high wind, hailstorms, lightning, and flash floods and mitigation efforts are directed at these components. Flash floods are the number one thunderstorm killer; lightning is second. The State Plan includes specific sections on lightning, tornadoes, and windstorms. For more information on these hazards see the specific sections. An average thunderstorm is roughly 15 miles in diameter and lasts about 30 minutes. During a thunderstorm, straight-line wind speeds can exceed 100 mph. Tornado winds can exceed 200 mph. These wind characteristics, along with hail and lighting, have resulted in death and injuries in Colorado presented in Table Colorado Natural Hazards Mitigation Plan 3 71

72 Table 3 26: Reported Thunderstorm Deaths, Injuries, and Total Damage in Colorado, 1960 to 2010 Weather Type Deaths Injuries Total Damage Lightning $3,130,000 Tornado $292,778,671 Wind $367,216,225 Hail $1,281,004,540 Source: NCDC Geographic Location Thunderstorms are quite prevalent along the Front Range to the eastern plains during the spring and summer. These often become quite severe and spawn tornadoes, strong winds, hail, and lightning. Looking at where lightning occurs helps describe where the most prevalent thunderstorm activity is in Colorado. The greatest number of lightning flashes is not found across the high mountain elevations, but rather where the mountains and plains intersect. More specifically, the Palmer Divide/Pikes Peak region, and to a lesser extent, the Raton Mesa/Southern Sangre De Cristo Mountains are the lightning prone areas in Colorado. Figure 3-21 shows the geographic distribution of annual average lightning flashes across the state. Colorado Natural Hazards Mitigation Plan 3 72

73 Figure 3 21: Colorado Convection Activity, 1989 to 2005 Several factors may enhance thunderstorm activity along the mountain and plains intersection. The flashes are concentrated on the eastern slopes of the major mountains which rise from the eastern plains. Regions of convergence related to the mountain and plains air flow may increase the likelihood for convection. High flash areas are also located near major west to east ridges which occur along the high plains. These ridges can provide regions of convergence in the lower atmosphere that further promote convection. Additionally, the low level moisture from the high plains of Colorado decreases the stability of the atmosphere near the mountains. Finally, the high flash areas also occur in the southern half of Colorado, which likely has more moisture associated with the southwest monsoon. Colorado Natural Hazards Mitigation Plan 3 73

74 Previous Occurrence Regular occurrences from spring through late summer or early fall. Most severe storms typically occur mid-summer. See thunderstorm specific hazards of hail, lightning, tornadoes, and windstorms for specific information. As shown in Figure 3-22, there is a demarcation along Colorado s Front Range between areas of greater number of thunderstorms to the east and a lesser number of days with thunder to the west. The San Luis Valley region in south-central Colorado has the least thunderstorm activity in the state. Figure 3 22: Average Number of Thunderstorm Days per Year in the United States Source: Valisala Future Probability The average annual number of severe thunderstorm watches issued per year across Colorado suggests the location where storms are possible. As shown in Figure 3-23, areas of the eastern plains average as high as 18 severe thunderstorm watches per year while areas of the central and southwestern mountains average less than one per year. Atmospheric activity producing conditions prone to thunderstorms are expected to occur in the future as in the past. See thunderstorm specific hazards of hail, lightning, tornadoes, and windstorms for specific information. Colorado Natural Hazards Mitigation Plan 3 74

75 Figure 3 23: Average Severe Thunderstorm Watches per Year in the United States, 1999 to 2008 Magnitude and Severity Thunderstorms may result in major or long-term property damage that threatens structural stability, isolated deaths and/or injuries, potential impact to critical services or facilities. Thunderstorms are a normal precursor to hazards such as flood, wind, hail, tornadoes, and lightning. Sources National Weather Service (NWS) National Climatic Data Center (NCDC) Vaisala Colorado Natural Hazards Mitigation Plan 3 75

76 Tornadoes Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Concentrated along the central and northern Front Range east to the Kansas Border. Includes east border counties. Most counties have recorded tornado events. Previous Occurrences Seasonally Regular occurrences throughout the summer storm season, primarily from May to August, peaking in June. Future Probability Expected Atmospheric activity producing conditions prone to tornadoes are expected to occur as in the past. Magnitude/Severity Catastrophic Destroyed or damaged property that threatens structural stability, mass fatalities and/or casualties, impact to critical lifelines, impact to government s ability to provide service. Likely to overwhelm state and local recourses and require Federal assistance for full recovery. Definition Tornado can be defined as a localized, violently destructive windstorm occurring over land, especially in the Midwestern United States and characterized by a long, funnelshaped cloud, composed of condensation and containing debris that extends to the ground and marks the path of greatest destruction. Tornadoes are generated by severe thunderstorms. Characteristics According to the National Oceanic and Atmospheric Administration, each year approximately 1,200 tornadoes are reported in the United States. Figure 3-24 shows the number of severe Colorado tornadoes per 3,700 square miles in comparison with the rest of the country. Colorado Natural Hazards Mitigation Plan 3 76

77 Figure 3 24: Tornado Activity in the United States Source: FEMA As a result of the frequency and destructiveness, over the past 30 years more than 100 federal disaster declarations included damage associated with tornadoes. The path of a single tornado can be miles long, but tornadoes rarely last longer than 30 minutes. A tornado can move as fast as 125 mph with internal wind speeds that can exceed 300 mph. Powerful tornadoes have lifted and moved objects weighing more than 300 tons a distance of 30 feet and tossed homes greater than 300 feet away from their foundations. Geographic Location In Colorado, the primary threat of tornado is east of the Continental Divide along the Front Range and foothill counties. Three counties, Adams, Weld, and Washington, all have over 100 reported tornadoes reported between 1950 and Weld County has the highest number of reported tornadoes in the state with 237 during this timeframe. Figure 3-25 shows additional information on the distribution of tornadoes across Colorado counties. Colorado Natural Hazards Mitigation Plan 3 77

78 Figure 3 25: Reported Tornadoes by County, 1950 to 2010 Detailed information on the specific number of tornadoes per county from 1950 to 2010 can be found in the section related to magnitude and severity below. Previous Occurrence In the last decade, Colorado averaged 44 tornadoes a year. However, the total number of events is variable from year to year. A record was reached in 1996, with a total of 98 tornadoes reported whereas in 2006, only 21 tornadoes were reported. Increasing population, improved communications, and more trained spotters have all resulted in more reported tornadoes each decade since the 1950s. Table 3-27 provides additional details of tornado events since the last PDMP update in Between January 2007 and April 2010, there were 219 reported tornado events in Colorado. Three (3) of the state s five (5) reported tornado deaths since 1950 occurred during this time period, in addition to 90 additional hazard related injuries and $152 million in property damage. Colorado Natural Hazards Mitigation Plan 3 78

79 Table 3 27: Tornado Events, Deaths, Injuries, and Damage in Colorado, 1/1/2007 to 4/30/2010 Year Reported Events Deaths Injuries Property Damage $4,098, $147,080, $860, $1,000 Totals $152,039,000 Source: NCDC Since the drafting of the 2007 State Plan, Colorado has experienced two significant tornado events that resulted in deaths and significant property damage. Although Colorado s overall death toll from tornadoes is relatively low over the last 60 years, the state s total deaths has increased from two (2) to five (5) since The following two events in the Town of Holly and Weld and Larimer Counties, related to 3 deaths, occurred in 2007 and 2008 and are described by the National Climatic Data Center below: With a maximum rating of EF3 and a maximum damage path width of 900 yards, the tornado raced through Holly, causing two fatalities and nine injuries. Over 200 residences and other buildings were affected or destroyed. Two people were killed and nine others were injured. The damage path was around 28 miles long...extending into Kiowa County. The last substantial damage with the tornado was 12 miles north of Holly...in northeast Prowers County...where a ranch sustained high end EF3 damage. A powerful tornado swept north northwestward across Weld County and into Larimer County, carving a path of destruction, nearly 39 miles in length. The tornado, up to one mile wide at times, initially touched down northeast of Platteville and finally lifted 6 miles west northwest of Wellington. A tornado assessment in the aftermath of the tornado revealed extensive areas of damage. On the enhanced Fujita Scale there were pockets of EF3 damage, mainly near the Missile Silo Park Campground, and to businesses and home in eastern Windsor. There was one fatality, and 78 injuries. One man was killed when he tried to escape the trailer park in his motor home. Preliminary estimates from FEMA indicated 850 homes were damaged, and nearly 300 homes were significantly damaged or destroyed. Privately insured damages totaled $147 million, and the Poudre Valley Rural Electric Associated reported $1 million of damage to electric transmission lines. Future Probability On average, most tornadoes in Colorado occur in June, followed by July and May, mainly during afternoon or evening hours. With increased coverage of Doppler radar, the increasing population, and greater attention to storm and tornado chasing, there is a resulting increase in the number of tornado reports over the past several decades. This can create the appearance of an increasing trend in tornado frequency when the increase in numbers can be attributed to Colorado Natural Hazards Mitigation Plan 3 79

80 advances in technology and reporting. Table 3-28 shows how the number of reported tornadoes has regularly increased since the 1950s. Table 3 28: Tornado Events, Deaths, Injuries, and Damages in Colorado by Decade, 1950 to 2010 Years Count Deaths Injuries Property Damage Crop Damage Total Damage $659,000 0 $659, $1,269,000 0 $1,269, $10,685,000 0 $10,685, $69,005,000 0 $69,005, $34,814,000 $6,503,000 $41,317, $170,596,000 $2,000 $170,598, * $1,000 0 $1,000 Total 1, $287,029,000 $6,505,000 $293,534,000 *Through April 2010 Source: NCDC The average annual number of tornado watches issued per year across Colorado suggests the locations where conditions for tornadoes are possible. As shown in Figure 3-26, areas of the eastern plains average as high as 7 tornado watches per year while the central and western regions of the state average less than one tornado watch per year. Atmospheric activity producing conditions prone to tornadoes are expected to occur as in the past and there was little change in the distribution of tornado events since the last plan update in Therefore, the number and severity of tornadoes in Colorado should continue in the future similar to the past. Colorado Natural Hazards Mitigation Plan 3 80

81 Figure 3 26: Average Tornado Watches per Year in the United States, 1999 to 2008 Magnitude and Severity Most of Colorado s tornadoes are generally weak, with wind speeds of less that 110 mph or referred to as an F1 or F0 on the standardized Fujita Scale. As shown in Table 3-29, 449 of the 460 tornadoes occurring in Colorado between 2000 and 2010 were of these weaker classifications. However, strong tornadoes do occur in the state. During this timeframe, 4 tornadoes were F3 (severe) while another 7 were F2 (significant). Colorado Natural Hazards Mitigation Plan 3 81

82 Table 3 29: Colorado Tornado Numbers and Strength, 2000 to 2010, with Fujita Scale Description Scale Count Percent Phrase Wind Speed Type of Damage F % Severe Tornado MPH Roof and some walls torn off well constructed houses; trains overturned; most trees in forest uprooted F % Significa nt Tornado MPH Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated. F % Modera te Tornado MPH The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed. F % Gale Tornado MPH Some damage to chimneys; breaks branches off trees; pushes over shallow rooted trees; damages to sign boards. Source: NCDC, Tornado Project Online Since 1915, there are reports of 40 deaths and 554 injuries resulting from tornadoes in Colorado. The majority of deaths (35) occurred prior to The number of deaths has significantly decreased as warning technology has advanced, and since 1950 only five (5) deaths are attributed to this hazard. Similarly, only 260 injuries were reported from tornadoes over this same 60-year period. Colorado Natural Hazards Mitigation Plan 3 82

83 Table 3-30 describes the human and financial losses reported from 1950 to Table 3 30: Tornado Events, Deaths, Injuries, and Damages in Colorado by County, 1950 to 2010 County Reported Property Deaths Injuries Events Damage Crop Damage Total Damage Adams $26,786,000 $6,500,000 $33,286,000 Alamosa $22,000 $0 $22,000 Arapahoe $9,430,000 $0 $9,430,000 Archuleta $1,000 $0 $1,000 Baca $2,969,000 $0 $2,969,000 Bent $1,416,000 $0 $1,416,000 Boulder $283,000 $0 $283,000 Broomfield $0 $0 $0 Chaffee $25,000 $0 $25,000 Cheyenne $2,552,000 $3,000 $2,555,000 Clear Creek $0 $0 $0 Conejos $25,000 $0 $25,000 Costilla $5,000 $0 $5,000 Crowley $28,000 $0 $28,000 Custer $5,000 $0 $5,000 Delta $25,000 $0 $25,000 Denver $32,575,000 $0 $32,575,000 Dolores $0 $0 $0 Douglas $990,000 $0 $990,000 Eagle $25,000 $0 $25,000 El Paso $9,646,000 $0 $9,646,000 Elbert $586,000 $0 $586,000 Fremont $54,000 $0 $54,000 Garfield $0 $0 $0 Gilpin $0 $0 $0 Grand $3,000 $0 $3,000 Gunnison $0 $0 $0 Hinsdale $0 $0 $0 Huerfano $528,000 $0 $528,000 Jackson $0 $0 $0 Jefferson $2,500,000 $0 $2,500,000 Kiowa $656,000 $0 $656,000 Kit Carson $379,000 $0 $379,000 La Plata $85,000 $2,000 $87,000 Lake $0 $0 $0 Larimer $65,000 $0 $65,000 Las Animas $290,000 $0 $290,000 Lincoln $29,333,000 $0 $29,333,000 Colorado Natural Hazards Mitigation Plan 3 83

84 County Reported Property Deaths Injuries Events Damage Crop Damage Total Damage Logan $3,345,000 $0 $3,345,000 Mesa $1,000 $0 $1,000 Mineral $10 $0 $10 Moffat $28,000 $0 $28,000 Montezuma $50,000 $0 $50,000 Montrose $23,000 $0 $23,000 Morgan $1,041,000 $0 $1,041,000 Otero $161,000 $0 $161,000 Ouray $0 $0 $0 Park $30,000 $0 $30,000 Phillips $828,000 $0 $828,000 Pitkin $25,000 $0 $25,000 Prowers $4,590,000 $0 $4,590,000 Pueblo $112,000 $0 $112,000 Rio Blanco $38,000 $0 $38,000 Rio Grande $3,000 $0 $3,000 Routt $3,000 $0 $3,000 Saguache $253,000 $0 $253,000 San Juan $0 $0 $0 San Miguel $0 $0 $0 Sedgwick $333,000 $0 $333,000 Summit $0 $0 $0 Teller $23,000 $0 $23,000 Washington $661 $0 $661 Weld $150,735,000 $0 $150,735,000 Yuma $3,364,000 $0 $3,364,000 Total 1, $286,273,671 $6,505,000 $292,778,671 Source: NCDC Colorado Natural Hazards Mitigation Plan 3 84

85 Tornadoes in Colorado s history causing death or significant injuries are listed and described in Table Table 3 31: Colorado Tornadoes Causing a Death or at Least Seven Injuries, 1950 to 2008 Date Deaths and Injuries Description JUN 30, dead 5 injured Three homes were destroyed on ranches and farms twenty miles southwest of Lamar, Bent County. AUG 10, dead 7 injured A man was killed when he took shelter in a dry goods store that was destroyed at Two Buttes, Baca County. NOV 4, dead 25 injured Unusual for the season, this tornado hit a farmhouse in Lincoln County, 20 miles north of Sugar City. NOV 4, dead 3 injured At the Pleasant Valley School eleven miles ESE of Holyoke a teacher was killed in her "teacherage" home. AUG 10, dead 8 injured Nine children and one woman died in a farmhouse near Thurman, Washington County. JUN 14, dead 2 injured A small tornado destroyed a poultry house and killed a child at Pueblo. AUG 10, dead 2 injured Two homes were destroyed on farms north of Padroni, Logan County. A child was killed. JUN 8, dead 4 injured Seven farms were devastated near the Colorado/Oklahoma border. Deaths were in Baca County. JUN 29, dead 50 injured Women died in each of two farmhouses that were completely leveled. This tornado passed just west of Johnstown. OCT 2, dead 4 injured Three people left their car and sought shelter in a farmhouse 14m NW of Fowler; the home and car were destroyed. APR 30, dead 12 injured Near McClave, Bent County, and Eads, Kiowa County, people were killed in the destruction of four different homes. JUN 27, dead 4 injured Ten miles north of Holyoke, Phillips County a massive tornado threw two cars a quarter mile. OCT 17, dead 9 injured A tornado struck a trailer park in the main street business district of Wray, Yuma County. Colorado Natural Hazards Mitigation Plan 3 85

86 Date Deaths and Injuries Description JUN 3, dead 42 injured Nearly 800 homes suffered damage as a tornado cut a swath through the heart of Thornton, a suburb of Denver. JUN 15, dead 7 injured Moving to the northeast then southeast and then to the south, a tornado cut an erratic path across south Denver. JUN 6, dead 14 injured A tornado destroyed 80% of the business district, of Limon, as well as 228 of the town's 750 homes. JLY 7, dead 8 injured The injuries were on farms that were torn apart near Bethune and Burlington, Kit Carson County. MAR 28, dead, 9 injured Over 200 residences and other buildings were affected or destroyed. Two people were killed and nine others were injured. The damage path was around 28 miles long. May 22, dead, 78 injured A powerful tornado swept northnorthwestward across Weld County and into Larimer County, carving a path of destruction, nearly 39 miles in length. Source: The Tornado Project Online Sources The Tornado Project Online Federal Emergency Management Agency (FEMA) National Climatic Data Center (NCDC) National Weather Service (NWS) Colorado Natural Hazards Mitigation Plan 3 86

87 Windstorms Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Concentrated along the Front Range, east central to northeast, and Grand Valley. Most counties have recorded windstorm events. Previous Occurrence Perennial Storms occur many times a year, often with widespread limited damage. Front Range and eastern Colorado experience seasonal high winds in Spring. Future Probability Expected Atmosphere conditions are expected to continue unchanged with windstorms remaining a perennial occurrence. Magnitude/Severity Moderate A typical wind event will cause limited property damage, occasional deaths, minor or no injuries, limited impact critical to services or facilities. Episodic and localized strong wind gusts or prolonged strong wind events with great affects on people and property. Definition Windstorms are defined as a storm with high winds or violent gusts. Chinook winds are warm dry wind that descends from the eastern slopes of the Rocky Mountains, causing a rapid rise in temperature. Sometimes these winds move at considerable force. Characteristics Two main causes of high winds in Colorado during the cold season are the air pressure difference between strong low pressure and cold high pressure systems, and Chinook winds developing along the Front Range and mountains in the eastern half of the state. A strong low pressure system in Colorado, coupled with a high pressure system to the west, can send a cold wind, called a Bora, through the western part of the state and down the slopes of the eastern mountains. The result can be a cascade of high winds from the west or northwest into the adjacent plains at speeds over 100 mph. The damage caused by this event is usually much more widespread than that caused by a severe thunderstorm in the warm season. Jet stream winds over Colorado are much stronger in the winter than in the warm season, because of the big difference in temperature from north to south across North America. Very swift west winds, under certain conditions, can bring warm, dry Chinook winds plowing down the slopes of the eastern mountains. These winds can also exceed 100 mph in extreme cases, again bringing the potential for widespread damage. Colorado Natural Hazards Mitigation Plan 3 87

88 The Chinook wind cycle that impacts Colorado s Front Range is shown in Figure Chinook winds can rise temperatures 25 to 35 degrees F within a short time. Chinook winds greatly moderate average winter temperatures in areas near enough to the mountains to experience them frequently. Due to these wind patterns, some locations in the eastern foothills are warmer than adjacent areas on the eastern plains on many days during the winter. Figure 3 2: Chinook Wind Cycle Dangers from high winds include flying debris, collapsed structures, and overturned vehicles. The National Weather Service will issue a high wind watch when there is a 50 percent or greater chance for high winds to develop in the next few days. When the threat becomes more certain in a specific area, a high wind warning will be issued. Cold strong winds can also bring dangerously low wind chill values, prompting a wind chill advisory or wind chill warning. Geographic Location According to Figure 3-28, the FEMA map of Wind Zones, Colorado falls into Wind Zones I, II, and III. Wind Zone I (130 mph) covers the Western Slope of Colorado, while Wind Zone II (160 mph) covers the central and eastern portion of the state. Wind Zone III (200 mph) reaches into Colorado s far eastern tier of counties. Colorado also has a large Special Wind Region along the Front Range due to the unique conditions related to the downslope Chinook and Bora winds. Colorado Natural Hazards Mitigation Plan 3 88

89 Figure 3 28: Wind Zones in the United States Source: FEMA Previous Occurrence Figure 3-29 combines high winds, strong winds, and thunderstorm winds as reported by the National Climate Data Center to show overall significant wind events. Colorado Natural Hazards Mitigation Plan 3 89

90 Figure 3 29: Reported Significant Wind Events by County, 1950 to 2010 Counties with the highest number of significant wind events reported between 1950 and 2010 tend to be located along the Front Range or northeast part of the state. However, one exception to the eastern counties is the Grand Valley which also experiences a high number of wind events. Along the Front Range, the counties of Larimer, Weld, Boulder, Jefferson, and Douglas all have a high number of reported wind events. Larimer had the highest number of significant wind events reported since 1950 with 293. The wind events in these counties also correlated with a high amount of property damage. High wind events were numerous in Yuma, Kit Carson, Morgan, Cheyenne, and Logan Counties on the eastern border and northeast. Shown in Table 3-32 are examples of hazardous wind events in Colorado. Each year, any number of dangerous and/or damaging wind events such as those described in the table occurs in the state. Colorado Natural Hazards Mitigation Plan 3 90

91 Table 3 32: Colorado High Wind Event Descriptions, 2007 to 2010 Date Event Description May 2010 May 2010 February 2009 June 2007 December 2008 High Wind High Wind Strong Wind Strong Wind High Wind Winds gusting up to 75 mph caused damage, especially over portions of El Paso and Pueblo Counties. Several large trees were uprooted in the Monte Vista area in Rio Grande County. A modular building was flipped on its top by the wind in Pueblo West. A few trees were also uprooted in the City of Pueblo. Winds caused power lines to come down in Manitou Springs, which sparked several small grass fires near the Pikes Peak Cog Railway. Three hangers at Peterson Air Force Base were evacuated, and some minor roof damage occurred. Some trees were uprooted in the greater Colorado Springs area. On Fort Carson, eight soldiers were injured when a tent they were setting up blew over. One soldier suffered a broken leg. Very strong winds developed in the Front Range Foothills as well as parts of the Interstate 25 Corridor. The winds downed trees and power lines and caused extensive property damage. Downed power lines sparked a 12 acre wildfire near Conifer. Scattered power outages were reported in the Big Thompson Canyon and in Loveland, affecting 460 residents and businesses. A tree was blown on to a vehicle in Greeley. Roof damage in addition to broken windows and skylights were observed in Boulder, Louisville and Longmont. A roof was blown off a home in Loveland. In Fort Collins, a nursery was badly damaged. The windstorm caused approximately $10,000 in damage to property and another $50,000 to the plants in the greenhouse. A strong wind gust blew a trailer in the path of two vehicles along State Highway 36, between Boulder and Lyons. The two vehicles were in the northbound lane when a wind gust blew a fifth wheel trailer into their path, as it approached from the opposite lane. The trailer left the road surface, and collided with the top left side of the first car, causing extensive damage. A van following the first vehicle then struck the trailer. The driver of the van suffered facial injuries. A strong southwest flow ahead of a cold front produced damaging winds across portions of western Colorado. Thousands of electrical customers were without power after widespread wind gusts of 45 to 56 mph downed some trees and large branches that were batted against and fell into power lines. Another brief period of high winds occurred in and near the foothills of Boulder and Jefferson Counties. In Nederland, the strong wind snapped a blue spruce which landed on a nearby propane tank. Some roofs in the immediate area were damaged. Power lines were also downed; which left 126 residences without electricity for about 6 hours. Peak wind gusts included 90 mph at the National Wind Technology Center, and 89 mph, 6 miles northwest of Boulder. Source: NCDC Colorado Natural Hazards Mitigation Plan 3 91

92 Future Probability Chinook winds are a fairly common wintertime phenomena in Colorado. These winds develop in well-defined areas and can be quite strong. Atmosphere conditions are expected to continue unchanged with windstorms remaining a perennial occurrence. Winds of 60 to near 100 mph are possible in and near the foothills in the Fort Collins, Boulder, Denver, Colorado springs, Canon City, Westcliffe, Walsenburg and Trinidad areas. The area around boulder is especially prone to these extreme wind events. In addition, Colorado will continue to experience Bora winds that will send winds in excess of 100 mph from the west and northwest and on to the eastern plains. These wind events can potentially cause more damage than a localized severe thunderstorm. Magnitude and Severity Windstorms in Colorado will typically blow shingles off roofs, knock down trees, down power lines, and overturn large semi-trailers. Wind may also damage antennas, communication towers, windows, siding of buildings, and vehicles. If the wind is strong enough and coming from the right direction, older or dilapidated structures or more vulnerable construction such as car ports may collapse. Building types, shapes, or additions that catch the wind, such as overhangs, canopies, and eaves, also tend to be affected by high wind. The state s most notable windstorms relative to insured property costs are shown in Table All of the most costly wind events shown are in the eastern part of the state, more notably focused on the Front Range. In 1982 and 1999, Boulder County and the Front Range experienced severe wind resulting in $20 million in insured costs for each event. The Boulder area has some of the highest peak winds in the United States. Table 3 33: Colorado s Most Costly Windstorms Date Location Cost When Occurred (Millions) April 8 10, 1999 Front Range $20.0 January 17, 1982 Boulder County $20.0 January 28 29, 1987 Front Range $10.0 December 30, 2008 Front Range, Colorado Springs, Eastern Plains $7.0 October 29, 1996 Front Range $5.2 February 2 3, 1999 Front Range $3.0 Source: Rocky Mountain Insurance Information Association Windstorms are one of Colorado s costliest hazards. Over the last 60 years, wind events have caused a reported $367 million in property and crop damage as listed in Table Deaths and injuries are also a result of wind events in the state with 21 and 406 respectively between 1950 and Colorado Natural Hazards Mitigation Plan 3 92

93 Table 3 34: Wind Events Deaths, Injuries, and Damage in Colorado by County, 1950 to 2010 Number of Property Crop Total County Deaths Injuries Events Damage Damage Damage Adams $7,232,000 $0 $7,232,000 Alamosa $898,000 $0 $898,000 Arapahoe $7,797,000 $0 $7,797,000 Archuleta $53,000 $0 $53,000 Baca $185,000 $0 $185,000 Bent $415,000 $0 $415,000 Boulder $35,366,000 $5,000 $35,371,000 Broomfield $0 $0 $0 Chaffee $143,000 $0 $143,000 Cheyenne $65,000 $0 $65,000 Clear Creek $0 $0 $0 Conejos $0 $0 $0 Costilla $0 $0 $0 Crowley $0 $0 $0 Custer $0 $0 $0 Delta $551,000 $0 $551,000 Denver $25,000 $0 $25,000 Dolores $1,965,000 $0 $1,965,000 Douglas $35,401,000 $0 $35,401,000 Eagle $2,000 $0 $2,000 El Paso $1,977,000 $0 $1,977,000 Elbert $29,941,000 $5,000 $29,946,000 Fremont $6,303,000 $0 $6,303,000 Garfield $1,000 $0 $1,000 Gilpin $0 $0 $0 Grand $9,934,000 $0 $9,934,000 Gunnison $1,936,000 $0 $1,936,000 Hinsdale $50,000 $0 $50,000 Huerfano $0 $0 $0 Jackson $20,000 $0 $20,000 Jefferson $35,290,000 $0 $35,290,000 Kiowa $100,000 $0 $100,000 Kit Carson $196,000 $0 $196,000 La Plata $1,041,000 $0 $1,041,000 Lake $0 $0 $0 Larimer $35,367,000 $0 $35,367,000 Las Animas $102,000 $0 $102,000 Lincoln $27,000 $0 $27,000 Logan $30,130,000 $0 $30,130,000 Mesa $1,833,000 $0 $1,833,000 Colorado Natural Hazards Mitigation Plan 3 93

94 Number of Property Crop Total County Deaths Injuries Events Damage Damage Damage Mineral $0 $0 $0 Moffat $20,000 $25,000 $45,000 Montezuma $232,000 $0 $232,000 Montrose $54,000 $0 $54,000 Morgan $33,816,000 $50,000 $33,866,000 Otero $301,000 $0 $301,000 Ouray $0 $0 $0 Park $1,683,000 $0 $1,683,000 Phillips $5,406,000 $0 $5,406,000 Pitkin $0 $0 $0 Prowers $166,000 $0 $166,000 Pueblo $3,810,000 $0 $3,810,000 Rio Blanco $156,000 $0 $156,000 Rio Grande $7,508,000 $0 $7,508,000 Routt $110,000 $0 $110,000 Saguache $338,000 $0 $338,000 San Juan $1,943,000 $0 $1,943,000 San Miguel $0 $0 $0 Sedgwick $32,745,000 $0 $32,745,000 Summit $0 $0 $0 Teller $6,493,000 $0 $6,493,000 Washington $240,225 $0 $240,225 Weld $27,533,000 $0 $27,533,000 Yuma $231,000 $0 $231,000 Total 3, $367,131,225 $85,000 $367,216,225 Sources Source: NCDC University of Calgary National Climatic Data Center (NCDC) National Weather Service (NWS) National Oceanic and Atmospheric Association (NOAA) Rocky Mountain Insurance Information Association (RMIIA) Colorado Climate Center (CCC) Colorado Natural Hazards Mitigation Plan 3 94

95 Winter Weather Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Snowfall amounts vary with elevation with greater amounts in the mountains, lower amounts in the plains and select southern and western regions. Previous Occurrence Seasonal September through April is primary season for significant snowfalls, with December/January producing colder and dryer snow storms while March/April producing wet and heavy snowfall. Snowfall may occur at high elevations throughout the year. Future Probability Expected Atmospheric activity producing conditions prone to winter weather such as ice, snow, extreme cold, and high winds are expected to occur as in the past. Magnitude/Severity Extensive Isolated but potentially major property damage that threatens structural stability, isolated deaths and/or injuries, potential impact to critical services or facilities. Definition Hazardous winter weather includes events related to heavy snow, blowing snow, ice, sleet or freezing rain, and extreme cold temperatures. Blizzards are severe winter storms that pack a combination of blowing snow and wind resulting in very low visibilities. While heavy snowfalls and severe cold often accompany blizzards, they are not required. Sometimes strong winds pick up snow that has already fallen, creating a blizzard. Characteristics Every state in the continental United States and Alaska has been impacted by severe winter storms. In Colorado, blizzards may occur during fall, winter and spring on the eastern high plains. While Colorado blizzards are less frequent and drop less snow than in areas further east and north, they can still be devastating. As recently as 1997 several fatalities were directly attributable to an October blizzard which caught many travelers unprepared. Heavy snows in the high mountains are much more common. Each year several lives are lost due to avalanches. Avalanches pose a serious problem to residents, road maintenance crews and back country travelers. Considerable effort is made each year to predict and manage avalanches. Colorado Natural Hazards Mitigation Plan 3 95

96 Late spring snow storms are not uncommon in Colorado. On May 3, 2001, a late spring storm hit, dumping snow across a large area of the state. In Denver, measurable snow has been recorded as late as June 12 back in Geographic Location Nowhere in the state is immune to the adverse impacts of Colorado s severe winter weather. Figure 3-30 shows that average snowfall is 72 inches or greater in the central (including the Front Range foothills) and western areas of the state. Figure 3 30: Annual Mean Total Snowfall in the United States In addition to snowfall, Table 3-35 depicts that anywhere in the state may experience extremely cold temperatures. Of counties with data, all have recorded temperatures of at least 22 degrees below zero. Table 3 35: Extreme Cold Temperatures in Colorado by County, County Extreme Temperature (F) County Extreme Temperature (F) Adams 33 La Plata 35 Alamosa 42 Lake 55 Arapahoe 32 Larimer 39 Archuleta 42 Las Animas 32 Baca 26 Lincoln NA Bent 29 Logan 35 Boulder 34 Mesa 36 Chaffee 32 Mineral 45 Cheyenne 30 Moffat 61 Colorado Natural Hazards Mitigation Plan 3 96

97 County Extreme Temperature (F) County Extreme Temperature (F) Clearcreek 33 Montezuma 27 Conejos 34 Montrose 23 Costilla 38 Morgan 32 Crowley NA Otero 28 Custer 41 Ouray 22 Delta 31 Park 54 Denver 25 Phillips 33 Dolores 36 Pitkin NA Douglas 35 Prowers 28 Eagle 51 Pueblo 30 El Paso 35 Rio Blanco 48 Elbert 38 Rio Grande 41 Fremont 25 Routt 45 Garfield 38 Saguache NA Gilpin NA San Juan 39 Grand 46 San Miguel 32 Gunnison 60 Sedgwick 37 Hinsdale 38 Summit 46 Huerfano 36 Teller NA Jackson 50 Washington NA Jefferson 41 Weld NA Kiowa 27 Yuma NA Kit Carson 29 *As Recorded At NRCS (U.S.D.A.) Temperature And Precipitation Stations (TAPS). Note: Not All Data Covers A 30 Year Period. Previous Occurrence Source: NRCS In 1983, an extremely bitter cold spell occurred with mercury dipping to 21 degrees below zero, the coldest recorded temperature in over 20 years. The October 1997 blizzard dumped as much as 31 inches of snow on metro Denver travelers were stranded at the Denver International Airport during the blizzard of The October 1997 blizzard cost air carriers more than $20 million. In April 2001, a severe storm caused over $4 million in damage to rural electric association power lines and poles. Thousands of homes were without power for days. The Denver International Airport lost power two times in two consecutive weekends due to two severe spring storms. Table 3-36 shows additional historic winter weather storm events in the state. Colorado Natural Hazards Mitigation Plan 3 97

98 Table 3 36: Historic Winter Weather Events, 1978 to 2009 Year Description Mar 3, 1978 riding winds up to 40 dumped up to 16 inches of snow in the Colorado Rockies ski country, 10 inches on Kansas and Nebraska and 8 inches in southern Iowa. It lay down a belt of ice south of the snow belt. The National Weather Service it a " dangerous winter. storm" and sent out a... From Late Winter Storm Lashes Rockies, Plains, Midwest. Related web pages news.google.com/newspapers?id=ddswaaaaibaj... Nov 21, 1979 The storm, which the US Weather Service called dangerous, virtually paralyzed a region stretching from northern New Mexico across Colorado into southern Wyoming and eastward into South Dakota, Nebraska, Kansas and the panhandles of Oklahoma and Tex as. Hundreds of schools closed.... From Winter Storm Buries Region. Related web pages news.google.com/newspapers?id=tuadaaaaibaj... Dec 26, 1982 A storm that buried Colorado in up to 4 feet of snow moved on Saturday, leaving behind closed roads and airports and thousands of stranded travelers, as ram and record warm temperatures in many Midwestern cities melted hopes for a white Christmas. At least two people in Colorado froze... From Winter Storm Leaves Colorado Buried. Related web pages news.google.com/newspapers?id=zuisaaaaibaj... Nov 28, 1983 A major winter storm lingered unexpectedly over Denver and eastern Colorado Sunday, all but isolating about 2 million people in nearly two... Blizzard warnings were posted Sunday night for northeast Colorado and winter storm warnings were issued in the southeastern part of the state.... From 2 Million All but Isolated by Colorado Storm Related web pages pqasb.pqarchiver.com/latimes/access/ Dec 14, 1984 A winter storm already blamed for 11 deaths stretched from the southern Rockies to the Great Lakes today after burying parts of Arizona and Colorado under 20 inches of snow, unleashing torna does in Texas and downing ice lad en power lines in Kansas.... From Winter Storm Extends to Great Lakes Related web pages pqasb.pqarchiver.com/latimes/access/ Nov 13, 1985 Winter storm warnings we're issued for much of Utah, Colorado and southern Wyoming, with up to 2 feet of snow predicted for the Colorado mountains by tonight. In Wyoming, 5 inches of snow fell Tuesday night at Rawlins. Afton received 3 inches of snow in just one hour.... From Rockies Remain Under Winter Storm Warnings. Related web pages news.google.com/newspapers?id=1aimaaaaibaj... Feb 27, 1987 Alpine, Ariz., had a winter snow cover of 82 inches, and snow was still falling at midday, National Weather Service officials said.... Thirty avalanches were reported in the Colorado mountains as the storm slowly moved eastward. Colorado Springs, Colo., received 14 inches of snow.... From Rockies, Plains Get More Snow From Tenacious Winter Storm Related web pages pqasb.pqarchiver.com/latimes/access/ Dec 31, 2006 DENVER A fleet of small planes canvassed snow covered roads in Colorado on Sunday, searching for stranded travelers after a powerful winter storm piled drifts up to 10 feet (3 meters) high across much of the Plains. National Guard troops have rescued 44 people from the storm,... From Motorists After Powerful Winter Storm Hits Colorado Local News News Related web pages Dec 26, 2007 By Peter M. Fredin, AP. DENVER (AP) Snow was falling again in Colorado on Thursday as the second winter storm in two days moved across the state. The latest storm is expected to pile as much as 20 inches of new snow in areas that have already been hit a series of year end storms.... From Winter storm dumps more snow on Colorado USATODAY.com Related web pages Dec 22, 2009 DENVER, Colo. A Winter Weather Advisory was issued for the Denver metro area Tuesday as the first of two storms moved into Colorado, promising measurable snowfall for much of the state in time for the Christmas holiday. "We're really talking about two weather systems hitting the... From Winter Storm will make Christmas white, or white ish, in Colorado KDVR Related web pages winter storm story... Source: Google Search for Colorado Winter Storm History Colorado Natural Hazards Mitigation Plan 3 98

99 Hazardous winter weather may result from bitterly cold temperatures rather than snow events. Table 3-37 lists winter weather events related to extreme cold temperatures that impacted property and agricultural crops across the state. Table 3 37: Extreme Cold Temperatures in Colorado, 1983 to 2009 Date Description, including Deaths, Injuries, Crop and Property Damage ($Million) 1983 Cold spell. Readings to 21F, coldest recorded temperature in 20 years Extreme cold, snow, wind. Main airport closed. Poor visibility. 46 car pile up on I 25 MAR 1995 APR 1995 JAN 1996 FEB 1996 MAR 96 DEC 1996 DEC 1996 JAN 1997 APR 1997 APR 1997 OCT 1997 JUN 1998 DEC 1998 JAN 1999 APR 1999 JUN 1999 JUN 2001 DEC 2005 DEC 2009 Freeze. West Colorado. Readings below critical values in orchard areas. 10% of crops damaged. Extreme Cold. Arapahoe area. Readings to 13F. Wheat damaged. ~ $1M crop damage. Extreme wind chill. Southeast. Wind chills from 30 to 50F. Extreme wind chill. Southeast plains. Wind chill 25 to 50F. Lows Pueblo 26F, Colorado Springs 18F. Extreme wind chill. Southeast. Bitter cold, gusty. Wind chill 25 to 40F. Extreme wind chill. East central, northeast. Readings 30 to 45 F. South central, southeast. Wind chill 20 to 40F. Denver area. Low 9F. Extreme wind chill. Southeast. Wind chills of 20 to 35F. Extreme wind chill. Southeast, foothills. Wind chills 25 to 35F. Northeast. Wind chill 25 to 50F. Extreme cold. East central. Single digit temperatures, highs below freezing, freezing drizzle, light snow. Schools closed 1 2 days for ice. Many car accidents. Freeze. West. Temperatures dropped below critical levels for most fruit varieties. Majority of stone fruits lost, most apples and pears survived. ~ $9M crop damage Blizzard. Front range, east. Snow to 4 in foothills. Gusts to 70 mph. Wind chill 25 to 40F. State of emergency declared. 5 deaths; 2 injuries; 24,000+ cattle lost Extreme cold. East central. Record cold AM temperatures, lows below freezing. Crop and garden damage. Extreme cold. Denver, northeast. 6 days dipped below 0F. Low 19F. Power outages, cracked water pipes. 5 deaths; 15 injuries Extreme wind chill. Far eastern Colorado. Readings below 35F. Extreme cold. Mesa County. Ruined part of fruit crop. Lows 10s to 20sF. ~$8.8M crop damage Extreme cold. Southwest. Late freeze destroyed grapes and vegetables. ~$0.004M crop damage Extreme cold. Hard freeze in southwest Colorado. Temperatures 25 and 30 degrees for several hours with widespread damage to pinto bean and tomato crops near Cortez. Extreme cold and wind chill. Record breaking cold temperatures in western Colorado. Frozen water pipes burst in many areas. Extreme wind chill. Wind chill values of 25 to 30. Temps from 5 to 15 degrees. Source: NCDC Colorado Natural Hazards Mitigation Plan 3 99

100 Two of the past three presidential declarations in Colorado have been related to severe winter weather events. In 2003, Colorado received a presidential declaration for snow emergency for the winter snowstorms of March 17th through the 20th. Twenty-nine counties requested assistance. The state and communities received $6.2 million in federal funds through the public assistance program. No hazard mitigation funds were included with the emergency declaration. In April 2001, the state incurred severe winter storms including high winds and ice, snapping power poles and downing lines, leaving many residents and businesses without power. The state requested and received a presidential disaster declaration for severe winter storms. Over $550,000 was received in hazard mitigation funds. In October 1997, the state declared an emergency for severe snowfalls. In December 2006, two federal and state emergencies were declared as a result of two major snowstorms. Future Probability Atmospheric activity producing conditions prone to winter weather such as ice, snow, extreme cold, and high winds are expected to occur. Every county is at risk from severe winter weather effects including cold temperatures, ice, heavy snow, and high winds. Magnitude and Severity Winter storms can result in flooding, closed highways, blocked roads, downed power lines and hypothermia. It is not unusual for motorists and residents to become stranded or for power outages to occur. Annually, heavy snow loads and frozen pipes cause damage to residences and businesses. Late season heavy snows will typically cause some plant and crop damages. The Rocky Mountain Insurance Information Association (RMIIA) estimates the blizzard of March 2003 was the most expensive winter storm from snow and ice damage in Colorado history. Table 3-38 shows an estimated price tag was at least $93.3 million from more than 28,000 claims filed ($108.8 million in 2009 dollars). Most of the larger carriers activated their emergency catastrophe teams who specialize in handling disaster claims. This estimate is for damage to homes and automobiles and excludes the large commercial building losses resulting from the blizzard. Table 3 38: Colorado's Losses Due to Winter Related Storms Date March 18 19, 2003 Oct , 1997 Sept. 20, 1995 Dec , 1982 Cost $93.3 million $10.5 million $6.4 million $4.9 million Source: RMIIA Colorado Natural Hazards Mitigation Plan 3 100

101 RMIIA reports that the majority of 2003 blizzard damage was the result of wet, heavy snow that collapsed roofs, porches, awnings, carports and outbuildings. There was also significant damage from downed trees and limbs, along with claims for wind, snow melt leakage, food spoilage and out-of-pocket living expenses for people forced out of their home due to storm damage. Most of the vehicle damage was due to being crushed rather than weather-related accidents. For the 2003 storms, the average cost per homeowner insurance claim was more than $3,500 and many homes were completely destroyed due to roof collapses and structural damage. Table 3-39 shows that total damage from this hazard over the last 60 years is reported at nearly $250 million. In addition to property damage, winter weather in Colorado has resulted in the reported deaths of 136 persons and injuries to 126 since Table 3 39: Winter Weather Deaths, Injuries, and Damage in Colorado by County: 1960 to 2008 County Number of Events Deaths Injuries Property Damage Crop Damage Total Damage Adams $8,661,075 $376,807 $9,037,882 Alamosa $1,006,709 $111,448 $1,118,157 Arapahoe $7,966,122 $376,807 $8,342,929 Archuleta $972,392 $103,407 $1,075,799 Baca $1,493,544 $2,782,960 $4,276,504 Bent $1,493,544 $2,782,960 $4,276,504 Boulder $11,403,478 $367,679 $11,771,157 Broomfield $6,206,375 $0 $6,206,375 Chaffee $1,548,423 $114,906 $1,663,329 Cheyenne $1,256,486 $1,283,045 $2,539,531 Clear Creek $4,724,258 $286,888 $5,011,146 Conejos $1,029,341 $111,781 $1,141,122 Costilla $1,026,047 $111,313 $1,137,360 Crowley $1,312,642 $282,628 $1,595,270 Custer $1,250,876 $111,313 $1,362,189 Delta $965,711 $4,777,022 $5,742,733 Denver $7,675,826 $110,159 $7,785,985 Dolores $971,985 $190,105 $1,162,090 Douglas $10,701,760 $110,159 $10,811,919 Eagle $991,579 $106,543 $1,098,122 El Paso $5,724,185 $282,655 $6,006,840 Elbert $1,565,054 $282,764 $1,847,818 Fremont $1,636,691 $161,323 $1,798,014 Garfield $965,209 $7,856,063 $8,821,272 Gilpin $4,719,779 $283,763 $5,003,542 Grand $4,520,431 $198,698 $4,719,129 Gunnison $975,064 $3,875,823 $4,850,887 Colorado Natural Hazards Mitigation Plan 3 101

102 County Number of Events Deaths Injuries Property Damage Crop Damage Total Damage Hinsdale $975,517 $100,407 $1,075,924 Huerfano $1,199,304 $111,405 $1,310,709 Jackson $4,494,469 $159,903 $4,654,372 Jefferson $11,329,895 $282,572 $11,612,467 Kiowa $1,492,493 $2,782,960 $4,275,453 Kit Carson $1,327,056 $283,207 $1,610,263 La Plata $1,007,392 $105,438 $1,112,830 Lake $1,378,180 $114,906 $1,493,086 Larimer $11,330,466 $367,679 $11,698,145 Las Animas $1,388,017 $282,503 $1,670,520 Lincoln $1,278,899 $283,045 $1,561,944 Logan $1,454,409 $423,178 $1,877,587 Mesa $964,137 $11,576,897 $12,541,034 Mineral $1,065,704 $100,407 $1,166,111 Moffat $963,991 $106,063 $1,070,054 Montezuma $972,370 $190,105 $1,162,475 Montrose $969,911 $7,040,438 $8,010,349 Morgan $7,564,953 $427,235 $7,992,188 Otero $1,484,070 $282,628 $1,766,698 Ouray $973,235 $3,869,605 $4,842,840 Park $4,705,292 $287,347 $4,992,639 Phillips $1,449,523 $423,178 $1,872,701 Pitkin $972,755 $106,657 $1,079,412 Prowers $1,492,480 $2,782,960 $4,275,440 Pueblo $1,416,213 $282,628 $1,698,841 Rio Blanco $1,023,991 $106,063 $1,130,054 Rio Grande $998,129 $111,781 $1,109,910 Routt $1,005,470 $106,532 $1,112,002 Saguache $1,077,595 $111,781 $1,189,376 San Juan $972,517 $99,938 $1,072,455 San Miguel $975,006 $190,105 $1,165,111 Sedgwick $1,449,523 $423,178 $1,872,701 Summit $4,477,424 $114,781 $4,592,205 Teller $1,767,240 $283,888 $2,051,128 Washington $1,471,909 $423,178 $1,895,087 Weld $7,970,667 $422,261 $8,392,928 Yuma $1,476,076 $5,423,178 $6,899,254 Total 3, $181,080,864 $68,029,034 $249,109,898 Source: SHELDUS Colorado Natural Hazards Mitigation Plan 3 102

103 Sources Rocky Mountain Insurance Information Center (RMIIA) Colorado Climate Center (CCC) Spatial Hazard Events and Losses Database for the United States (SHELDUS) Federal Emergency Management Agency (FEMA) National Climatic Data Center (NCDC) National Resources Conservation Service (NCRS) Google.com Colorado Natural Hazards Mitigation Plan 3 103

104 Geologic Hazards Avalanche Earthquake Erosion and Deposition Expansive Soils Landslides, Mud/Debris Flows, Rockfalls Subsidence Colorado Natural Hazards Mitigation Plan 3 104

105 Avalanche Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Concentrated west of Interstate 25 in the higher elevations of the mountains. Previous Occurrences Seasonal Occur every year commonly from November through April. Not all avalanche paths run every year. Many run only once every 5 to 15 years, and others even less frequently. Future Probability Expected Atmospheric conditions resulting in appropriate snow conditions for avalanche are expected to occur in the future as in the past. Known avalanche areas will typically continue to produce events. Magnitude/Severity Extensive Limited property damage that does not typically threaten structural integrity; annual deaths (6 7 per year) and multiple injuries; little or no impact on critical services or facilities. Definition An avalanche is a mass of snow, ice, and debris; flowing and sliding rapidly down a steep slope. Avalanches are also referred to as snow slides. Snow avalanches are defined in Colorado state statutes as a geologic hazard. Characteristics Snow avalanches occur in the high mountains of Colorado seasonally as the result of heavy snow accumulations on steep slopes. When the snow pack becomes unstable, it suddenly releases and rapidly descends downslope either over a wide area or concentrated in an avalanche track. Avalanches reach speeds of up to 200 miles an hour and can exert forces great enough to destroy structures and uproot or snap off large trees. It may be preceded by an "air blast" which also is capable of damaging buildings. Avalanche paths consist of a starting zone, a track, and a runout zone. In general the runout zone is the critical area for land use decisions because of its otherwise attractive setting for development. Avalanche-prone lands may pass many winters or even decades without a serious avalanche. Only part of an avalanche may release at once. Lack of vegetation or a predominance of quick-growing aspen and low shrubs often characterize active portions of an avalanche track and the runout zone, readily identifying the seasonal peril. Colorado Natural Hazards Mitigation Plan 3 105

106 Avalanches are triggered by natural causes or human actions. Natural causes include earthquakes, thermal changes, and blizzards. Ice slabs falling off cornices may trigger avalanches. Human activities, such as snowmobiling, snowboarding, skiing, hiking, driving or setting off explosions may trigger an avalanche. Loss of life of backcountry skiers, snowboarders, backpackers, climbers, and snowmobilers due to suffocation is the principal danger. Geographic Location The greatest avalanche threats are in the mountainous areas of the Western United States including Alaska. The Colorado Geological Survey (CGS) and the Colorado Avalanche Information Center (CAIC) have mapped the State s areas susceptible to avalanche activity. The CAIC forecasts backcountry avalanche and mountain weather conditions for 10 Zones in the mountains of Colorado, shown in Figure Figure 3 31: Colorado Avalanche Zone Boundary Map Colorado Natural Hazards Mitigation Plan 3 106

107 Previous Occurrences Hundreds of snow avalanches happen each winter, most of them in remote places. Historic significant avalanche events and others resulting in loss of life since 1993 are listed and described in Table Table 3 40: Significant Avalanches by Location, Year Description Deaths 1993 Heavy snow. Southwest. Highest snowfall Road closures Heavy snow. Mountains. I 70 avalanche. Cars, truck buried Heavy snow to 2. Mountains, southwest Heavy snow (1 5 ), high winds. Southwest. 200 hunters lost, stranded Heavy snow. Mountains, Front Range. Mountain snow to 8. Road closures Heavy snow to 2. Central, northern, southwest mountains. I car pile up. Roads closed Avalanche. San Bernardo Mountain Avalanche. Ophir Gulch Avalanche. Near Gladstone Preseason skier. Telluride Ski Area Two skiers triggered avalanche at Aspen Highlands Ski Area Human triggered avalanche on Grand Mesa. Snowmobiler buried Cumberland Pass area Avalanche. Hurricane Gulch Avalanche. Highland Peak Diamond Peaks. Backcountry snowboarder buried Ohio Pass. Backcountry skier killed Farwell Mountain. Backcountry skier Crystal Peak, Tenmile Range. Backcountry snowmobiler Yankee Doodle Lake. Backcountry skiers Aspen Highlands. Skier killed Crystal Peak. Backcountry skier Miner Basin. Snowmobiler Aspen Mountain. Skier Ashcroft. Four backcountry skiers Telluride. Snowboarders Pagoda Peak. Three snowmobilers Burro Mountain. Snowmobilers Clear Creek County. Damage to Silver Plume water treatment plant s chlorine contact building and tank. I 70 frontage road blocked. Clear 0 Creek dammed up. Utility line down Grand Mesa. Crossed Highway 65. Colorado Natural Hazards Mitigation Plan 3 107

108 Year Description Deaths 2004 La Plata Peak. Snowshoers Mt. Huron. Snowshoer & skier Closure of Red Mountain, Molas and Coal Bank Passes. Front Range Wireless/Verizon Cell building destroyed Soda Mountain. Backcountry skier Aspen Highlands area. Skier Quandary Peak. Climbers Grand Mesa. Skier Arapahoe Basin. Skier Mines Peak. Snowboarder Kelso Mountain. Hikers Trap Park area. Snowmobilers Mt Shimer, near Aspen. Skiers South of Echo Lake, near Mt Evans. Snowshoer North Mountain. Snowmobiler Snowmass. Skier Cameron Pass. Snowmobiler Little Box Canyon. Snowmobiler East Vail backcountry. Snowboarder Gravel Mountain, north of Granby. Snowmobilers Northwest of Crested Butte. Snowmobiler Near Aspen Ski Area. Skier Bartlett Mountain near Fremont Pass. Skier Apache Peak, Indian Peaks. Skier Steep Gully #1, west of Arapahoe Basin Ski Area. Snowboarder Battle Mountain, Vail side country. Snowboarder Southwest of Creede. Other Near the Ridgway Hut, San Juan Mountains. Skier Lindley Backcountry Hut south of Aspen. Skier Near Antora Peak south of Buena Vista. Snowmobiler Near Baldy Peak, east of Ridgway. Climber. 1 Source: NCDC, CAIC Case History On the afternoon of February 23, 1961, two women left the groomed ski slopes at Aspen to ski in unblemished snow of a small basin near the main ski run. The avalanche hazard was high and warnings had been published and posted. The experienced skiers whisked out onto the slope and down, intent on skiing toward and then through a small stand of timber. When the first skier reached the bottom of the slope, her companion had Colorado Natural Hazards Mitigation Plan 3 108

109 vanished. Less than an hour later the missing skier was found suffocated under three feet of snow from a small avalanche that ran only 90 feet. In 1972, a subdivision near Vail was allowed in an avalanche path not far from the ski area and construction began on condominiums. The builder was stopped after financial institutions withdrew money from the project on learning it was in an avalanche path and mud flow zone. Today the development is but a concrete foundation a monument that property damage can be prevented and lives saved by responsible action. The geologically hazardous area is now zoned for open space. The case is a landmark example of what can happen when land-use regulations are legally circumvented and the builder s and the public s best interests are ignored. In March 2010, a group of five snowmobile riders were enjoying a day in the backcountry in remote and technical terrain. The area sees very little snowmobile use through the winter as it requires advanced riding skills. The victim was caught in the avalanche unknown by his party. The party presumably drove up to the accident site within minutes, noticed the avalanche but did not see the victim. The party searched with their avalanche beacons near the snowmobile for up to 45 minutes. One of the party members decided to ride further up the slope to get better cell phone reception. While riding, his beacon, still on receive, picked up the victim's signal. The victim was found in approximately 15 minutes (total search time was approximately 1 hour and 20 minutes), buried approximately 3 feet deep and approximately 100 yards uphill from the snowmobile. Future Probability Avalanche-prone areas may pass many winters or even decades without a serious avalanche with many running only once every 5 to 15 years, and others even less frequently. When avalanches do occur, it is most common between November and April. Not all avalanche paths run every year, and when they do they may not run the full length of their paths. Avalanches may stop in the starting zone, track, or run-out zone, depending on the amount and condition of the snow in the path. Because it is difficult to accurately capture the number of avalanches occurring in any given year, looking at the number of fatalities by county may provide an idea of where to focus mitigation activities. The American Institute for Avalanche Research and Education reports that 90 percent of avalanche victims die in slides triggered by themselves or a member of their group. By obtaining a better understanding of outdoor recreation in avalanche-prone areas may lend toward a better understanding of future probability for this hazard. Figure 3-32 shows that between 1950 and 2008, Pitkin County experienced 38 avalanche fatalities in the state, followed closely by Summit County with 36. Clear Creek County has the third highest number of deaths during this time period with 23. Other counties with ten or greater avalanche deaths over the last 60 years include Gunnison, Chaffee, Ouray, Lake, Eagle, San Miguel, Larimer, and Grand. Colorado Natural Hazards Mitigation Plan 3 109

110 The Colorado Department of Transportation s (CDOT) Avalanche Atlas has over 522 known avalanche paths. CDOT regularly monitors and/or controls over 278 avalanche paths. Table 3 32: Colorado Avalanche Fatalities by County, Magnitude and Severity Avalanches are not a hazard until human activities and land uses are affected adversely by the avalanches. Possible conflicting land uses between humans and avalanches are recreation, residential, transportation, and mining. Examples of this conflict would include property damage, injury, deaths and excessive maintenance costs. Avalanches are extremely destructive due to the great impact forces of the rapidly moving snow and debris and the burial of areas in the runout zone. Structures not specifically designed to withstand the impacts are generally totally destroyed. Where avalanches cross highways, passing vehicles can be swept away, demolished and their occupants killed. Snow avalanches also imperil cross-country skiers, downhill skiers, and snowmobilers and several of the backcountry visitors perish each winter. Residences planned or erected in avalanche runout zones may not qualify for financing or insurance. Colorado Natural Hazards Mitigation Plan 3 110

111 The maximum measured impact pressure of an avalanche is 10 ton/ft (2) while 1 ton/ft (2) is more common. A typical range is form 0.5 to 5.0 ton/ft (2). Air blasts from powder avalanches commonly exert a pressure of 100 lb/ft (2) of force. Pressures of only lb/ft (2) are capable of knocking out most windows and doors. Additional damages associated with impact pressure are shown in Table Table 3 41: Damage Related to Avalanche Impact Pressures Impact Pressure (lbs/ft2) Potential Damage Break windows Push in doors, damage walls, roofs 200 Severely damage wood frame structures Destroy wood frame structures, break trees Destroy mature forests >6000 Move large boulders Sources: CGS, FEMA Roads, highways, and railroads are blocked for hours, or sometimes days, every year due to avalanches. Many skiers, other winter sportsmen, and travelers have been injured or killed by avalanche activity. Loss of Life Most avalanche related deaths occur from winter sports and recreation activities. Some deaths result from highway maintenance and response activities. Although it is difficult to determine the number of persons at risk from avalanche, Colorado has averaged 6 to 7 deaths per year over the last 10 years. There have been avalanche fatalities and accidents in Colorado every month of the year. Over the last 10 winters in the United States an average of 25 people died in avalanches every year. Every fatal accident is investigated and reported, so those numbers can be reported with some certainty. There is no way to determine the number of people caught or buried in avalanches each year, because non-fatal avalanche incidents are increasingly under reported. The average yearly property loss was $31,200, though property loss varied greatly from year to year. Figure 3-33 depicts the number of avalanche fatalities in the United States by state for winter seasons 1950 to 2008/09. Colorado leads the country with 224 deaths attributed to avalanches during this time period, 100 greater deaths than the next highest state. Colorado Natural Hazards Mitigation Plan 3 111

112 Table 3 33: Avalanche Fatalities by State, 1950 to 2009 As shown in Figure 3-34, the number of seasonal avalanche fatalities in the United States by has increased significantly since Factors explaining this reported increase include a greater number of people recreating in avalanche prone areas and enhanced tracking and reporting of incidents. Colorado Natural Hazards Mitigation Plan 3 112

113 Table 3 34: Avalanche Fatalities by winter, 1950 to 2008 Figure 3-35 shows statistics gathered from 1950 through the 2008/09 season and indicates that most avalanche deaths in the United States occurred from avalanches while riding a snowmobile. The number of deaths attributable to climbers and hikers and backcountry skiers follow closely with 177 and 162 respectively. Besides outdoor recreationists, other populations at risk of avalanches include motorists, residents, and workers. Since 1950, it is reported that 13 motorists, 30 residents, 23 ski patrollers and rescuers, 13 highway personnel, and 28 others at work have died as a result of avalanches in the United States. These groups of people are also at risk to avalanches in Colorado. Colorado Natural Hazards Mitigation Plan 3 113

114 Table 3 35: Avalanche Fatalities by Activity, 1950 to 2009 Fatalities by Activity /09 Snowmobiler Climber/Hiker Backcountry Skier Out of Bounds Skier 77 Snowboarder (BC and OB) Snowshoer Misc Recreation In Area skier/boarder Motorist 13 Resident Others at work Ski Patroller Highway Personnel 13 Rescuer Source: Colorado Avalanche Information Center Property Damage Lack of recognition of avalanche runout potential (the farthest reach of debris) has resulted in residential building construction within runout zones in Colorado. When the infrequent, large avalanche event occurs, damage to these buildings will occur unless measures are taken to protect existing structures. Property damage can occur throughout the entire avalanche path. Impact (air or snow) damage ranges from minor to major structural damage to any structure within the path. Vehicles and equipment can be moved great distances and damaged. When deposited, the debris associated with the avalanche might cause damage and be expensive to remove. Table 3-42 provides a summary of avalanche events and associated property damage in Colorado from the National Climatic Data Center. Recorded property damage is relatively low with a total of $313,500 over the last 50 years. Colorado Natural Hazards Mitigation Plan 3 114

115 Table 3 42: Avalanche Damage in Colorado by County: 1960 to 2008 County Number of Events Property Damage Alamosa 1 $0 Archuleta 2 $22,422 Boulder 5 $8,333 Broomfield 1 $8,333 Chaffee 3 $0 Clear Creek 4 $0 Costilla 1 $0 Custer 1 $0 Delta 6 $2,500 Dolores 2 $22,422 Eagle 6 $367 Fremont 1 $0 Garfield 7 $367 Gilpin 3 $0 Grand 6 $0 Gunnison 9 $22,222 Hinsdale 4 $22,422 Huerfano 1 $0 Jackson 1 $0 Jefferson 4 $8,333 La Plata 2 $22,422 Larimer 2 $0 Mesa 4 $2,500 Moffat 1 $0 Montezuma 4 $27,922 Montrose 5 $0 Ouray 3 $22,222 Park 3 $0 Pitkin 13 $367 Rio Blanco 1 $0 Routt 3 $0 Saguache 1 $0 San Juan 6 $97,922 San Miguel 8 $22,422 Summit 7 $0 Total 131 $313,500 Source: SHELDUS Colorado Natural Hazards Mitigation Plan 3 115

116 Infrastructure Roads, highways and railroads may become blocked and damaged by avalanche snow and debris. During the 2007/08 avalanche season, CDOT experienced 1,128 hours of road closures, at various locations statewide, due to avalanche control. CDOT also spent 8,406 hours performing avalanche mitigation activities and cleanup. In addition to delaying highway and rail travel, it is costly to clear the transportation routes. In a few cases, where avalanches threaten access roads to mountaintop radio and microwave communication sites, emergency repairs and maintenance are delayed. In areas where efforts are underway to control avalanches, the maintenance of avalanche control structures and/or explosive control is costly. Table 3-43 shows roadway infrastructure at risk from avalanches. Table 3 43: Major Colorado Roadways at Risk from Avalanche US Hwy 550 The Battleship (Arnold) path, 3.55 miles north of Silverton, San Juan Mountains US Hwy 550 West Riverside path, about 7.7 miles north of Red Mountain Pass, San Juan Mountains US Hwy runs in an 8 mile stretch US Hwy 6 Loveland Pass Area US Hwy 6 Silver Plume Area, new path in 2003 CO Hwy 82, selected areas US Hwy 40, selected areas US Hwy 160, selected areas I 70 between Denver and Vail Source: CDOT Sources Colorado Department of Transportation (CDOT) Colorado Geological Survey (CGS), Colorado Avalanche Information Center (CAIC) Spatial Hazard Events and Losses Database for the United States (SHELDUS) Federal Emergency Management Agency (FEMA) National Weather Service, National Climatic Data Center (NCDC) Martinelli, speech from November 8, 1973 Colorado Natural Hazards Mitigation Plan 3 116

117 Earthquake Much of the information presented in this section comes from the Colorado Geological Survey (CGS) and the Earthquake Evaluation Report which is an annex to the State Plan. Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Recorded earthquakes are located over a large area of the state. However, faults with capacity for larger magnitude events are in central and western Colorado. Previous Occurrences Sporadic More than 500 earthquake tremors of magnitude 2½ or higher have been recorded in Colorado since Higher magnitude earthquakes have only occurred a few times in the last 150 years. Future Probability Occasional Although on average, several earthquakes are expected to occur in the state, they are likely to be of smaller magnitude. A 5+ magnitude is expected once or twice per decade based on historic trend. Magnitude/Severity Catastrophic Destroyed or damaged property that threatens structural stability, mass fatalities and/or casualties, impact to critical lifelines, impact to government s ability to provide service. Likely to overwhelm state and local recourses and require Federal assistance for full recovery. Definition Earthquakes are the vibrations or shaking created when large blocks of Earth s crust move with respect to one another. The break between these blocks is a fault. Virtually all earthquakes in the Earth s crust occur from movement on faults, or less frequently through volcanic or magmatic activity. Characteristics Many earthquakes in Colorado occur naturally; many are caused by human actions. Humans may trigger earthquakes through different types of activities including oil and gas extraction, reservoir impoundment, fluid injection, or mining. The most intense shaking experienced during earthquakes generally occurs near the rupturing fault, and decreases with distance away from the fault. In a single earthquake, however, the shaking at one site can easily be 10 times stronger than at another site, even when their distance from the ruptured fault is the same. Colorado Natural Hazards Mitigation Plan 3 117

118 Seismic events may lead to landslides, uneven ground settling, flooding, and damage to homes, dams, levees, buildings, power and telephone lines, roads, tunnels, and railways. Broken natural gas lines may cause fires. Magnitude and intensity are used to describe seismic activity. Magnitude (M) is a measure of the total energy released. Each earthquake has one magnitude. Intensity (I) is used to describe the effects of the earthquake at a particular place. Intensity differs throughout the area. A scale commonly used to measure magnitude is the Richter Scale whereas the Modified Mercalli Scale (MMI) is used for intensity. Geographic Location Although many of Colorado s earthquakes occurred in mountainous regions of the state, some have been located in the western valleys and plateau region or east of the mountains. Thousands of faults have been mapped in Colorado, but scientists think only about 90 of these were active in the past 1.6 million years. Figure 3-36 shows the locations of medium to large earthquakes in Colorado over the last century. Portions of the state show clustering such as near the Denver metro region, central mountains, and the southwestern and northwestern part of the state. Northeast Colorado is largely void of seismic activity. Figure 3 36: Earthquakes in Colorado, Source: Colorado Geological Survey Colorado Natural Hazards Mitigation Plan 3 118

119 The Sangre de Cristo Fault, which lies at the base of the Sangre de Cristo Mountains along the eastern edge of the San Luis Valley, and the Sawatch Fault, which runs along the eastern margin of the Sawatch Range, are two of the most prominent potentially active faults in Colorado. Not all of Colorado s potentially active faults are in the mountains and some cannot be seen at the earth s surface. For example, the Cheraw Fault, which is in the Great Plains in southeast Colorado, appears to have had movement during the recent geologic past. The Derby Fault near Commerce City lays thousands of feet below the earth s surface but has not been recognized at ground level. Previous Occurrence More than 500 earthquake tremors of magnitude 2.5 or higher have been recorded in Colorado since More earthquakes of magnitude 2.5 to 3 probably occurred during that time, but were not recorded because of the sparse distribution of population and limited instrumental coverage in much of the state. For comparison, more than 20,500 similar-sized events have been recorded in California during the same time period. Table 3-44 provides a list of Colorado s larger earthquakes. The largest known earthquake in Colorado occurred on November 7, 1882 and had an estimated magnitude of 6.5. The location of this earthquake, which has been the subject of much debate and controversy over the years, appears to be in the northern Front Range west of Fort Collins. Table 3 44: Notable Earthquake Events in Colorado: 1870 Through 2000 Date Location Magnitude (M) and Intensity (I) M I 12/04/1870 Pueblo Ft. Reynolds VI 10/1871 Lily Park, Moffat Co. VI 09/17/1880 Aspen VI 11/07/1882 North central Colorado 6.5* VII 12/1891 Maybell VI 11/15/1901 Buena Vista VI 11/11/1913 Ridgway area VI 09/09/1944 Montrose Basalt VI 08/03/1955 Lake City VI 10/11/1960 Montrose/Ridgway 5.5 V 01/04/1966 Northeast of Denver 5.0 V 01/23/1966 Southern Colorado 5.5 VII 08/09/1967 Northeast of Denver 5.3 VII 11/27/1967 Northeast of Denver 5.2 VI *Estimated, based on historical felt reports. Sources: Colorado Earthquake Project 1999; National Earthquake Information Center; The Denver Business Journal 11/26 12/2/1999 Colorado Natural Hazards Mitigation Plan 3 119

120 Case History The strongest earthquake in Colorado during the past century and a half was of magnitude 6.6. This 1882 earthquake frightened people in Denver and other northern Front Range cities. It was so strong that the bolts holding the electric generators for Denver were snapped off and power was knocked out. The location of the earthquake was uncertain for over a century. However, careful research by CGS scientists in 1986 determined that the earthquake was centered about ten miles north of Estes Park. Research by USGS scientists in 1996 confirmed this conclusion. The most economically damaging earthquake in Colorado s history occurred on August 9, 1967 in the Denver metropolitan area. This magnitude 5.3 earthquake caused more than a million dollars damage in Denver and the northern suburbs. This earthquake is believed to have been induced by the deep injection of liquid waste into a borehole at Rocky Mountain Arsenal. Future Probability Because the occurrence of earthquakes is relatively infrequent in Colorado and the historical earthquake record is short (only about 140 years), it is challenging if not impossible to accurately estimate the timing or location of future dangerous earthquakes in Colorado. Although limited, available seismic hazard information can provide a basis for a reasoned and prudent approach to seismic safety. Scientists are constantly studying faults in Colorado to determine future earthquake potential. Based on the historical earthquake record and geologic studies in Colorado, an event of magnitude 6.5 to 7.5 could occur somewhere in the state. Figure 3-37 shows levels of horizontal shaking that have a 2-in-100 chance of being exceeded in a 50-year period. The areas of Red indicate a higher risk of shaking from an earthquake while white indicates the lowest. Colorado falls in the lower to middle range of this indicator. Colorado Natural Hazards Mitigation Plan 3 120

121 Figure 3 37: National Seismic Hazard Map, 2008 Source: United States Geological Survey Magnitude and Severity The most economically damaging earthquake in Colorado s history occurred on August 9, 1967 in the Denver metropolitan area. This magnitude 5.3 earthquake caused more than a million dollars damage in Denver and the northern suburbs. The August 1967 earthquake was followed by an earthquake of magnitude 5.2 three months later in November Although these earthquake events 1967 cannot be classified as major earthquakes, they should not be discounted as insignificant. They occurred within Colorado s Front Range Urban Corridor, an area where nearly 75 percent of Colorado residents and many critical facilities are located. Since March 1971, well after the initial flurry of seismic activity, 15 earthquakes of approximate magnitude 2.5 or larger have occurred in the vicinity of the northern Denver suburbs. Relative to other western states, Colorado s earthquake hazard is higher than Kansas or Oklahoma, but lower than Utah, and certainly much lower than Nevada and California. Even though the seismic hazard in Colorado is low to moderate, it is likely that future damaging earthquakes will occur. It is prudent to expect future earthquakes as large as magnitude 6.5, the largest event of record. Calculations based on the historical earthquake record and geological evidence of recent fault activity suggest that an earthquake of magnitude 6 or greater may be expected somewhere in Colorado every several centuries. Colorado s earthquake hazard and risk has historically been rated lower than most knowledgeable scientists in the state consider justified. As a result, local emergency Colorado Natural Hazards Mitigation Plan 3 121

122 managers are generally unaware of the size and consequences of an earthquake that could occur in the state. HAZUS 99 gave a probabilistic Annualized Earthquake Loss (AEL) of $5.8 million which ranked Colorado 30th in the nation. The Colorado Geological Survey ran a series of deterministic scenarios for selected faults around the state using HAZUS MH. The earthquake magnitudes used for each fault were the Maximum Credible Earthquake taken from the USGS Quaternary Fault and Fold Database or from the USGS National Earthquake Hazard Map. The results demonstrate that the probabilistic AEL value of $5.8 million does not begin to convey the size of the loss that would occur in the event of a strong earthquake on any of these faults. For example, a magnitude 6.5 earthquake on the Golden fault is forecast to result in a $22 billion economic loss. Or, consider that a magnitude 6.0 earthquake under the Rocky Mountain Arsenal would result in $3.9 billion economic loss to Adams County alone; and a loss ratio of 17% that would make recovery difficult. Figure 3-38 shows the estimated economic losses based on the scenarios as described above. All of the affected areas are near densely populated areas with high numbers of homes, businesses, and associated infrastructure. The areas include the Denver metro and the Colorado Springs region. Colorado Natural Hazards Mitigation Plan 3 122

123 Figure 3 38: Top Five (5) Earthquake Potential for Direct Economic Loss Source: Colorado Geological Survey, Earthquake Evaluation Report Scenarios from the Earthquake Evaluation Report also determined estimates for loss of life. If any of the top earthquakes were to occur from the map above, hundreds of lives would be lost. Sources The Denver Business Journal Spence, W., Langer, C.J., and Choy, G.L., 1996, Rare, large earthquakes at the Laramide deformation Front Range Colorado (1882) and Wyoming (1984): Seismological Society of America Bulletin, v. 86, no. 6, p Colorado Geological Survey (CGS) Southern California Earthquake Center National Earthquake Information Center United States Geological Survey (USGS) Kirkham and Rogers, 1986 Colorado Natural Hazards Mitigation Plan 3 123

124 Erosion and Deposition The Colorado Geological Survey (CGS) is the primary source for the information related to expansive soils and deposition as described below. Hazard Profile Summary Consideration Impact Description Geographic Location Statewide All counties experience erosion and deposition activities either through human caused disruption of the land or natural causes. Previous Occurrences Perennial Erosion and deposition is an ongoing natural event and a concern whenever human activities disrupt the land. Future Probability Expected This is an ongoing natural event which is aggravated by human activities that disturb the land. These natural and human activities are expected to continue as in the past. Magnitude/Severity Moderate Limited or short term property damage; no deaths or few injuries; little or no impact or critical services or facilities. May be a precursor to Rockfalls and landslides. Typically a slow moving event. Definition Erosion is the removal and simultaneous transportation of earth materials from one location to another by water, wind, waves, or moving ice. Deposition is the placing of the eroded material in a new location. All material that is eroded is later deposited in another location. Characteristics All the geologic processes that make available more material for erosion and deposition tend to increase the rates of each process. This is particularly true for landslides, mud flows, debris flows, earthflows, rock falls, and physical and chemical weathering. These processes also involve erosion and deposition which frequently makes more material vulnerable to erosion. Erosion and deposition is typically initiated by water or wind in Colorado. Riverine erosion is the long-term process whereby river banks and riverbeds are worn away. This process is best described as a River s tendency for constant course alteration, shape and depth change, and the balancing act between the water s sediment transport capacity and its sediment supply. Swiftly moving floodwaters cause rapid local erosion as the water carries away earth materials. Deposition occurs where flood waters slow down, pool or lose energy in other ways and the materials settle out. Figure 3-39 describes the relationship between stream flow velocity and particle erosion, transport, and deposition. Colorado Natural Hazards Mitigation Plan 3 124

125 Table 3 39: Erosion and Transport Characteristics of Streamflow Velocity Source: PhysicalGeography.net Wind erosion is when wind is responsible for land removal, movement, and deposition. Wind erosion most commonly occurs from exposed areas such as fields, tailings and desert areas when the wind is strong and the materials are deposited when the wind diminishes. Another factor that controls the amount of erosion is the ease with which material can be dislodged. Hard granites erode very slowly while soft silts and sands erode very quickly. Geographic Location Erosion and deposition are occurring continually at varying rates all over Colorado. Point sources of erosion are common to construction sites or other areas where human interaction with the earth results in exposed soil or removal of vegetation. Natural waterways perpetually remove and carry soil from the earth to locations downstream. The Colorado River appears red during times of high run-off due to the amount of soil being carried. Erosion and deposition issues are also exacerbated in wildfire burn areas. Colorado Natural Hazards Mitigation Plan 3 125

126 Previous Occurrences Erosion and deposition is an ongoing natural event and a concern whenever human activities disrupt the land. Significant erosion and deposition is a post wildfire event issue in Colorado and areas of concern may be correlated with wildfire event locations. Case History Near Larkspur in Douglas County an access road and shallow borrow ditch were cut to serve an airport runway uphill from the access road. During construction of the road and borrow pit a large area was stripped of vegetation. Heavy water runoff from above the runway and the runway itself was channeled down the borrow ditch. There were no control features to slow the velocity of the water or retard erosion. Within five years the borrow ditch was eight feet deep. Properly designed and installed water control structures, revegetation of the graded area, detention ponds, drop structures, and other measures would have paid for themselves in later maintenance and repair costs. The Fountain Creek watershed near Colorado Springs presents erosion and deposition problems downstream to as far as La Junta. There were historic erosion problems through Woodland Park with associated sedimentation problems. Erosion problems are also evident in the stream banks upstream of the Old Crystola Road. Sedimentation and flooding occur downstream in many reaches causing issue during periods of high streamflow. Flooding and erosion in this watershed have accelerated the loss of aquatic and wetland habitats, contributed to the loss of hundreds of acres of productive farmland, and caused the foundations of roads and homes to crumble. Future Probability Erosion and deposition is a hazard event aggravated by natural events such as heavy rain or streamflow, high wind, wildfires, or human activities that disturb the land. These natural and human activities are expected to continue as in the past resulting in ongoing erosion and deposition. Magnitude and Severity Erosion can result in minor inconveniences or total destruction. Severe erosion removes the earth from beneath bridges, roads and foundations of structures adjacent to streams. By undercutting it can lead to increased rockfall and landslide hazard. The deposition of material can block culverts, aggravate flooding, destroy crops and lawns by burying them, and reduce the capacity of water reservoirs as the deposited materials displace water, and cause overall degradation of the water supply. Human activities greatly influence the rate and extent of erosion and deposition. Stripping the land surface of vegetation, altering natural drainages, and rearranging the earth through construction of highways, subdivision development, farmland preparation, Colorado Natural Hazards Mitigation Plan 3 126

127 and modification of drainage channels for water control projects are significant factors in increased erosion and deposition. Natural causes such as wildfire are an additional precursor to soil erosion and deposition as runoff and permeability are changed by removal of vegetation and changes to the physical condition of the ground. Riverine erosion has many consequences including land and development loss. It can also affect marine transportation and channel navigation sources, cause increased harbor and river delta sedimentation, and degrade channel navigation. Other problems include water quality reduction due to high sediment loads, native aquatic habitat losses, damage to public utilities (roads, bridges and dams), and increase maintenance, prevention, and control costs. Wind erosion, hinders agricultural production from topsoil loss. Wind blown dust reduces visibility, causing automobile accidents and hindering machinery; and has a negative effect on air and water quality creating animal and human health concerns. Wind erosion also damages public utilities and infrastructure. Colorado has experienced dust storms in the southwest portion of the state that resulted in the deposition of particles on high mountain snow. Being less reflective than snow, the dust particles absorbed heat with the result of an earlier snowmelt in some areas of the state. Early snowmelt may result in water supply and recreational use issues on waterways. Sedimentation of streams degrades habitat essential for many aquatic organisms. Colorado s recreation-based economy depends highly on the quality of our waters for fishing, boating, and overall appeal of the states many river valleys. Sources Colorado Geological Survey (CGS) Fountain Creek Watershed District PhysicalGeography.net State of Alaska Hazard Mitigation Plan, 2010 Colorado Natural Hazards Mitigation Plan 3 127

128 Expansive Soils The Colorado Geological Survey (CGS) is the primary source for the information related to expansive soils described below. Hazard Profile Summary Consideration Impact Description Geographic Location Statewide Statewide with heaving bedrock concentrated along the front range. Previous Occurrences Perennial Ongoing event resulting from natural causes such as drought and precipitation and human caused development activities. Future Probability Expected Conditions related to natural causes such as precipitation and drought cycles in addition to development and land use prevalent in the past are expected to continue. Magnitude/Severity Extensive Major or long term property damage with potential to threaten structural integrity; Limited or no loss of life or injury; One of the Colorado s most prevalent causes of damage to buildings and construction. Definition Expansive, or swelling soils or rock, are defined as soils or soft bedrock that increase in volume as they get wet and shrink as they dry out. They are also commonly known as bentonite, expansive, or montmorillinitic soils. Characteristics Swelling soils contain a high percentage of certain kinds of clay particles that are capable of absorbing large quantities of water. Soil volume may expand 10 percent or more as the clay becomes wet. The powerful force of expansion is capable of exerting pressures of 20,000 psf or greater on foundations, slabs or other confining structures. Subsurface Colorado swelling soils tend to remain at constant moisture content in their natural state and are usually relatively dry at the outset of disturbance for construction on them. Exposure to natural or man-caused water sources during or after development results in swelling. In many instances the soils do not regain their original dryness after construction, but remain moist and expanded due to the changed environment. Technical Description Shrink Swell Potential of Soil Linear extensibility refers to the change in length of an unconfined clod as moisture content is decreased from a moist to a dry state. It is an expression of the volume change Colorado Natural Hazards Mitigation Plan 3 128

129 between the water content of the clod at 1/3- or 1/10-bar tension (33kPa or 10kPa tension) and oven dryness. The volume change is reported as percent change for the whole soil. The amount and type of clay minerals in the soil influence volume change. Linear extensibility is used to determine the shrink-swell potential of soils. The shrinkswell potential is low if the soil has a linear extensibility of less than 3 percent; moderate if 3 to 6 percent; high if 6 to 9 percent; and very high if more than 9 percent. If the linear extensibility is more than 3, shrinking and swelling can cause damage to buildings, roads, and other structures and to plant roots. Special considerations for structural design are common to mitigation against expansive soils. Local or site-specific soil survey data should indicate that an area contains soil with a high shrink-swell potential. Technical Description Heaving/Dipping Bedrock Heaving bedrock is a geological hazard that is related to expansive soils, but it is more complex in terms of its uplift morphologies, deformation mechanisms, and regional distribution. It is common along Colorado's Front Range piedmont where steeply dipping sedimentary bedrock containing zones of expansive claystone is encountered near to the ground surface. The heave features associated with heaving bedrock are distinctly linear and are caused by differential swelling and/or rebound movements within the bedrock. Heaving bedrock has caused exceptional damage to houses, roads, and utilities along the Front Range piedmont since suburban-type development began in the early 1970s. Much of this damage may be attributed to the longstanding tendency to assume that the bedrock may be treated, for site-exploration and design purposes, as an expansive soil having essentially uniform properties. This approach ignores the strong heterogeneity that is often present in the bedrock. Geographic Location Rocks containing swelling clay are generally softer and less resistant to weathering and erosion than other rocks and therefore, more often occur along the sides of mountain Valleys and on the plains than in the mountains. However, the potential for shrinking and swelling soils in Colorado is evaluated state-wide. Figure 3-40 shows expansive soils across the state. The darker the red coloring is shown on the map, the greater potential for shrinking and swelling soils. Colorado Natural Hazards Mitigation Plan 3 129

130 Figure 3 40: Expansive Soils in Colorado Soils in portions of Elbert, Lincoln, and Crowley Counties have very high linear extensibility, or the potential for shrinking and swelling. In addition, the northwestern Colorado counties of Moffat and Routt also have soil areas with high shrink and swell potential. Heaving bedrock is largely limited to an area along the central Front Range, affecting primarily Douglas and Jefferson Counties. Previous Occurrences About 50 percent of Colorado s soil has a high or very high potential for shrinking and swelling and is a perpetual natural phenomenon. Swelling is generally caused by expansion due to wetting of certain clay minerals in dry soils. Therefore, arid or semi-arid areas such a Colorado with seasonal changes of soil moisture experience a much higher Colorado Natural Hazards Mitigation Plan 3 130

131 frequency of swelling problems than eastern states that have higher rainfall and more constant soil moisture. Case History Several structures on the Southern Colorado State University Campus northeast of Pueblo have been damaged because swelling soils were not recognized or compensated for adequately in design, construction and maintenance of buildings, sidewalks, driveways, and water lines. Water percolating into dry soils exposed by construction excavation caused the clays to expand, exerting tremendous upward pressures. Floors, walls, ceilings, sidewalks, water lines, driveways, and other improvements have sustained an estimated $1.5 million in damages. In 1976 at the site of the new maximum security facility for the Colorado State Prison in Fremont County, swelling soils and bedrock were shown on geologic maps. Field investigations and soils tests resulted in a remedial plan by the geologic and soils engineers, architect, builder and others on foundation design, drainage and landscaping. Millions of dollars in potential damages were avoided. Future Probability Conditions related to natural causes such as precipitation and drought cycles in addition to development and land use prevalent in the past are expected to continue. Magnitude and Severity Swelling soils are one of the nation s most prevalent causes of damage to buildings and construction. Annual losses are estimated in the range of $2 billion. The losses include severe structural damage, cracked driveways, sidewalks and basement floors, heaving of roads and highway structures, condemnation of buildings, and disruption of pipelines and sewer lines. The destructive forces may be upward, horizontal, or both. Rocks containing swelling clay are generally softer and less resistant to weathering and erosion than other rocks and therefore, more often occur along the sides of mountain Valleys and on the plains than in the mountains. Because the population of Colorado is also concentrated in mountain valleys and on the plains, most of the homes, schools, public and commercial buildings, and roads in the state are located in areas of potentially swelling clay. Swelling clays are, therefore, one of the most significant, widespread, costly, and least publicized geologic hazards in Colorado. Damage from swelling clays can affect, to some extent, virtually every type of structure in Colorado. Some structures, such as downtown Denver s skyscrapers, generally have well engineered foundations that are too heavily loaded for swelling damage to occur. At the opposite extreme are public schools and single family homes, which are generally constructed on a minimal budget and which may have under-designed lightly loaded Colorado Natural Hazards Mitigation Plan 3 131

132 foundations that are particularly subject to damage from soil movements. Homeowners and public agencies that assume they cannot afford more costly foundations and floor systems often incur the largest percentage of damage and costly repairs from swelling soil. Design and construction of structures while unaware of the existence and behavior of swelling soils can worsen a readily manageable situation. Where swelling soils are not recognized, improper building or structure design, faulty construction, inappropriate landscaping and long term maintenance practices unsuited to the specific soil conditions can become a continuing, costly problem. Design problems might include improper foundation loading, improper depth or diameter of drilled pier, insufficient reinforcing steel, and insufficient attention to surface and underground water. Miscalculating the severity of the problem for a particular clay soil can result in damage although some mitigating measures were taken. Construction problems related to swelling soils include lack of reinforcing steel, insufficient or improperly placed reinforcing steel, mushroom-topped drilled piers, and inadequate void space between soils and grade beams. Allowing clays to dry excessively before pouring concrete and permitting the ponding of water near a foundation during and after construction also are contributing factors in swelling-soil related construction problems. Building without allowance for basement or ground floor movement in known swelling soils areas is a very common source of property damage. Improper landscaping problems include inadequate management of surface drainage and planting vegetation next to the foundation so irrigation water enters the soil. Sources Colorado Geological Survey (CGS) Colorado Natural Hazards Mitigation Plan 3 132

133 Landslides, Mud and Debris Flow, and Rockfalls The Colorado Geological Survey is the primary source for the information related to landslides, mud and debris flow, and rockfalls as described below. Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Concentrated along the Front Range, central mountains, and western part of the state and typically associated with areas of significant slope, grade, or overall elevation change. Previous Occurrences Perennial Land movement in the form of landslides, rockslides, and mud/debris flows are a natural and ongoing event. Human activity disrupting the land and periods of significant precipitation increases the likelihood of occurrence. Future Probability Expected Natural and human caused factors accounting for historic land movement is expected to continue. Magnitude/Severity Moderate Most events will have limited property damage that does not threaten structural integrity; limited or no deaths and injuries; little or no impact to critical services or facilities. However, single events may have significant impact such as deaths or cause significant damage to public infrastructure. Definition Landslides are the downward and outward movement of slopes composed of natural rock, soils artificial fills, or combinations thereof. Common names for landslide types include slump, rockslide, debris slide, lateral spreading, debris avalanche, earth flow, and soil creep. Mud flows are described as a mass of water and fine-grained earth materials that flows down a stream, ravine, canyon, arroyo or gulch. If more than half of the solids in the mass are larger than sand grains-rocks, stones, boulders, the event is called a debris flow. Rockfalls are the falling of a newly detached mass of rock from a cliff or down a very steep slope. Characteristics Landslides move by falling, sliding, and flowing along surfaces marked by differences in soil or rock characteristics. A landslide is the result of a decrease in resisting forces that hold the earth mass in place and/or an increase in the driving forces that facilitate its movement. The rates of movement for landslides vary from tens of feet per second to fractions of inches per year. Landslides can occur as reactivated old slides or as new slides in areas not previously experiencing them. Areas of past or active landsliding can Colorado Natural Hazards Mitigation Plan 3 133

134 be recognized by their topographic and physical appearance. Areas susceptible to landslides but not previously active can frequently be identified by the similarity of geologic materials and conditions to areas of known landslide activity. Debris and mud flows are a combination of fast moving water and a great volume of sediment and debris that surges down slope with tremendous force. The consistency is like that of pancake batter. They are similar to flash floods and can occur suddenly without time for adequate warning. When the drainage channel eventually becomes less steep, the liquid mass spreads out and slows down to form a part of a debris fan or a mud flow deposit. In the steep channel itself, erosion is the dominant process as the flow picks up more solid material. Any given drainage may have several mud flows a year, or none for several years or decades. They are common events in the steep terrain of Colorado and vary widely in size and destructiveness. Cloudbursts provide the usual source of water for a mud flow in Colorado. Rockfalls are the fastest type of landslide and occur most frequently in mountains or other steep areas during early spring when there is abundant moisture and repeated freezing and thawing. The rocks may freefall or carom down in an erratic sequence of tumbling, rolling and sliding. When a large number of rocks plummet downward at high velocity, it is called a rock avalanche. Rockfalls are caused by the loss of support from underneath or detachment from a larger rock mass. Ice wedging, root growth, or ground shaking, as well as a loss of support through erosion or chemical weathering may start the fall. Geographic Location Land movement related to landslides, mud and debris flows, and rockfalls occurs naturally across Colorado on an ongoing basis. Figure 3-41 shows areas prone to this hazard. Because this hazard is correlated with elevation change, this hazard largely occurs in the mountainous region from the Front Range to the West Slope. Colorado Natural Hazards Mitigation Plan 3 134

135 Section 3: Hazard Identification and Risk Assessment Figure 3 41: Colorado Landslide, Mudslide, Rockfall, and Debris Flow Areas The Colorado Landslide Mitigation Plan (2002) is attached to the overall PDM plan and provides details for specific areas across the state at most risk from landslides, debris flows, and rockfalls. In addition, the Colorado Department of Transportation, Materials and Geotechnical Branch, manages the state s soils and rockfall program. This agency is responsible for the Rockfall Mitigation Project Plan (RMPP) that includes a list of the 756 rockfall sites identified as having chronic rockfall problems. Previous Occurrences It is estimated that there are thousands of landslides in Colorado each year although the number, frequency, and severity fluctuate. Precipitation, topography, and geology affect landslides. For example, landsliding in areas of Colorado intensified during the 1980s and late 1990s due to higher than normal annual precipitation levels. Colorado Natural Hazards Mitigation Plan 3 135

136 It is estimated that at least 18 damaging debris flow events have occurred in Glenwood Springs since Garfield County, in 1985, recorded the largest debris flow in Colorado history, a 175-foot thick mass of debris a mile long and 1,000 feet wide. Table 3-45 and Table 3-46 provide a summary of notable landslide and mud flow events in Colorado from the early 1900s to Table 3 45: Notable Landslide Events in Colorado, 1903 to 1999 Year Location Description South of Glenwood Springs, Garfield Co. Brownville, Clear Creek Co. Telluride, San Miguel Co DeBeque Canyon 1930s 1940s Marble, Gunnison Co. Glenwood Springs, Garfield Telluride, San Miguel Co. Big Thompson Canyon, Larimer Co. Glenwood Springs, Garfield Co Ouray, Ouray Co. 1983, Dowds Junction, Eagle Co. 15 Western Slope Counties Grand Junction, Mesa Co. Two Western Counties El Paso County (and other counties for flood) Debris flow. Rainstorm caused mud and rock to cover a railroad line. Train wreck, one member of train crew killed. Debris flows. Community engulfed and destroyed. Debris flows in Coronet Creek, flooding in San Miguel River. Landslide. Blocked Colorado River, resulted in forced relocation of a small community, highway and railroad. Debris flows. Town nearly destroyed. Debris flow. Much of town covered. Mud 2 feet deep. Debris flows in Coronet Creek, flooding in San Miguel River. Interrelated landslide/ flood event. Mountain torrent flood. Debris flow. Losses between $500,000 $1 million. 200 acres of residential district covered up to 14 deep. Debris flows in Canyon, Cascade, Portland Creeks, etc. Flooding in Uncompahgre River. Landslides blocked I 70. Highway closed. Floods and landslides. Declared disaster areas by President. Related to spring runoff. Over $6.6 million spent in federal, state, and local disaster assistance. Most homes in a subdivision affected. Some condemned. Floods and landslides. State emergency declaration. $1.4 million in damages. Floods, mudslides, landslides. Presidential disaster declaration. Estimated over $30 million in infrastructure and property damage, including road repairs and twisted utility lines. Several residences condemned. Source: Colorado Landslide Hazard Mitigation Plan 1988, 2002 Colorado Natural Hazards Mitigation Plan 3 136

137 Table 3 46: Notable Mudslide Events in Colorado, 1984 to 2007 Year Location Description 1984 Approximately 7 miles SW of Telluride 1996 Approx. 1 mi. SW of Aspen Woman dies in mud slide; melting snow wrecks county roads A 24 year old woman student at Western State College in Gunnison died a gruesome death after the car she and a friend were driving back to school washed off Highway 145 near Trout Lake Sunday [May 13th] afternoon and tumbled about 150 feet before coming to rest upside down in the mud. The first debris flow came down the mountain [Keno Gulch] on Monday, May 13th at about 4:30 pm. A second came down the next day [Tuesday, May 14] at about 4:00 pm. The parking lot was covered with mud and debris about 5 ft thick, six cars were virtually buried (4 were totaled). The mud and debris flowed into and structurally damaged the Music Hall and partially filled the large pond beside the Music Hall. Neither flow was moving so fast that you couldn t walk away from it. (David Pearcy, Director, Aspen Day School, personal commun., 1996) 1997 I 70 near Palisade Four mile stretch of westbound I 70 closed due to mudslide El Paso County Floods, mudslides, landslides. Presidential disaster declaration. Estimated over $30 million in infrastructure and property damage, including road repairs and twisted utility lines. Several residences condemned Alpine, Chaffee County Case History Ninety eight people evacuated. $33,000 in infrastructure damage. Homes filled with mud, propane tanks pushed off foundations. Source: Telluride Times, 5/17/84, p. 1; Early on the morning of March 8th, 2010, a large rockfall in the Glenwood Canyon shut down the State s primary East-West thoroughfare, Interstate-70. Twenty boulders, ranging from 3 feet to 10 feet in diameter, fell on the interstate. As they fell, these heavy rocks punched many holes through the roadway, including one that was 20 feet by 10 feet. The largest boulder weighed 66-tons. Crews were able to restore one lane in each direction within four days, eliminating the 2-hour detour and preventing any long-term disruptions to tourism and the transportation industry. Had the Colorado Department of Transportation not been able to so quickly restore traffic-flow along I-70, there could have been significant impacts to the local and state economy. This would have included impacts on tourism and on the trucking industry. Between maintenance, traffic control and repairs, the total cost of the incident was $2,180,000. In June 1977, a residential subdivision developer in Jefferson County dug a utility trench half way up a 100-foot long slope contrary to the recommendations of an engineering geology report. Surface water collected in the improperly located and constructed trench Colorado Natural Hazards Mitigation Plan 3 137

138 causing a landslide 100 feet across, 50 feet long and up to 6 feet deep. It is not know if the costly remedial measures will prevent additional sliding and damage to property in the subdivision. An area being planned as a subdivision in Summit County was engulfed in a matter or minutes by a mudslide caused by saturated soils below the Town of Breckenridge water reservoir and a beaver pond. Geologic investigation showed several similar slides had occurred previously. The property lost its prime value and extensive regrading and mitigation work was required. No structures were involved. Rerouting drainage, drying out the slope, regrading and preventive construction measures should mitigate future damage as the area is developed. Following a week of daily low intensity rainstorms, a heavy rainstorm that dumped approximately 3 inches of rain between 6:30 and 7:30 pm on July 21, 2007 mobilized several debris flows ( mudslides ) in Weldon Gulch that impacted the town of Alpine, Colorado. Several structures, roads, and utilities were damaged and two nearby county roads had to be closed. The town and upstream communities were subsequently evacuated. Although no injuries or loss of life resulted, approximately 65 people are directly affected by the debris flow. In March 1974, a boulder the size of a small car hurtled down the steep west side of the Lyons hogback in Jefferson County. It bounced into a new subdivision and stopped after penetrating a wall in the back of an expensive home. No one was injured. Property damage was about $10,000, including the cost of measures to prevent similar incidents at that site in the immediate future. The incident could have been prevented easily in the subdivision development stage but it was not recognized. Future Probability Geologic hazards such as landslides, mud and debris flows, and rockfalls are sporadic and somewhat unpredictable, however, geologic studies can determine historic runs and existing movement in the earth suggesting movement is occurring or imminent. These events can occur at any time from almost any location along a slope, and occur regularly throughout any given year. What is more predictable is that the natural and human-caused factors accounting for historic land movement is expected to continue. Colorado Natural Hazards Mitigation Plan 3 138

139 Magnitude and Severity Landslides, mudslides, debris flows, and falling rocks damage and destroy homes, roads, railroads, pipelines, electrical and telephone lines, mines, oil wells, commercial buildings, canals, sewers, dams, bridges, seaports, airports, forests, parks, and farms. Earth movement hazards will also cause significant costs and delays to travelers, workers, the delivery of services, and local economies. Landslides in the United States are estimated to cause more than $1.0 billion a year in property damage, according to the Transportation Research Board of the National Academy of Sciences. Railroads, highways, homes, and entire communities are lost to landslides that demolish and/or bury them. In Colorado the 19th century mining camp of Brownsville just west of Silver Plume is buried beneath a rain-triggered landslide that became a debris flow. It is now under Interstate 70. Landslides occur commonly throughout Colorado, and the annual damage is estimated to exceed three million dollars to buildings alone. Mud/debris flows ruin substantial improvements with the force of the flow itself and the burying or erosion of them by mud and debris. The heavy mass pushes in walls, removes buildings from foundations, fills in basements and excavations and sweeps away cars, trucks heavy equipment and other substantial objects. Boulders and trees swept along by the muddy mass demolish buildings, and flatten fences and utility poles. In mountain areas, portions of valleys have been eroded to a depth of several feet by the flow process. Although rare, deaths and injuries occur from landslides. Table 3-47 shows that over the last 50 years, five (5) deaths and ten (10) injuries were reported in Colorado from this hazard. Garfield County, home to the rugged Glenwood Canyon, shows the most number of reported landslides and the highest amount of damages in the state. Colorado Natural Hazards Mitigation Plan 3 139

140 Table 3 47: Landslide Deaths, Injuries, and Damage in Colorado by County: 1960 to 2008 County Number of Events Deaths Injuries Total Damage Archuleta $714 Clear Creek $250,000 Delta $18,333 Denver $0 Dolores $714 Eagle $523,667 Garfield $1,660,417 Gunnison $20,333 Hinsdale $2,714 LaPlata $1,714 Mesa $88,750 Montezuma $714 Montrose $20,333 Ouray $2,000 Pitkin $523,667 San Juan $714 San Miguel $2,714 Total $3,117,500 Source: SHELDUS Sources TheDenverChannel.com (ABC 7 News) Colorado Geological Survey (CGS) National Academy of Sciences, Transportation Research Board Spatial Hazard Events and Losses Database for the United States (SHELDUS) Federal Emergency Management Agency (FEMA) United States Geological Survey (USGS) Colorado Natural Hazards Mitigation Plan 3 140

141 Subsidence The Colorado Geological Survey (CGS) is the primary source for the information related to subsidence and collapsible soils as described below. Hazard Profile Summary Consideration Impact Description Geographic Location Regional South central, southwest, and northwest are impacted by this hazard. Distributed across the state with areas of denser concentration in heavily mined areas. Previous Occurrences Perennial Ongoing event resulting from natural causes such as drought and precipitation and human caused development activities. Future Probability Expected Conditions related to natural causes such as precipitation and drought cycles in addition to development and land use prevalent in the past are expected to continue. Magnitude/Severity Extensive Major or long term property damage with potential to threaten structural integrity; Limited or no loss of life or injury; one of the Colorado s most prevalent causes of damage to buildings and construction. Definition Ground subsidence is the sinking of the land over man-made or natural underground voids. In Colorado, the type of subsidence of greatest concern is the settling of the ground over abandoned mine workings. Collapsing and settling soils are relatively low density materials that shrink in volume when they become wet, and/or are subjected to great weight such as from a building or road fill. The process of collapse with the addition of water is also known as hydrocompaction. Characteristics Natural and human activities cause subsidence. Activities that lead to subsidence include underground mining, pumping groundwater or petroleum out of the ground, hydrocompaction, and draining organic soils. Natural causes of subsidence include the development of sinkholes, rock sliding downward along faults, natural sediment compaction, and melting of permafrost. Subsidence may occur abruptly-virtually instantly or gradually over many years. It may occur uniformly over a wide area as local depressions or pits separated by areas which Colorado Natural Hazards Mitigation Plan 3 141

142 have not visibly subsided. In Colorado, it is most common in the sedimentary rocks over abandoned coal and clay mines. The crystalline rocks in which most metals are mined have greater strength and are less likely to settle or collapse. Subsidence can also occur where underground water has dissolved subsurface materials or has been withdrawn by wells. Although serious in other western states, these latter types of subsidence are less common in Colorado than sinking caused by the caving in of underground mine workings. Collapsing and settling soils have considerable strength when dry and generally are not a problem to structures and improvements. When they become wet, they are subject to rapid collapse and can be reduced in volume as much as 10 to 15 percent. Surface ground displacement of several feet can result. Similar processes frequently affect old landfills or poorly placed earth fills. Geographic Location Subsidence and collapsible soils tends to be problematic along the Front Range, Western Slope, in the central mountains near Eagle County, as shown in the map below. The eastern plains are largely void of this hazard. The largest concern for subsidence generally occurs where land with sedimentary rock is undermined around historic coal and clay mines. In addition to undermined areas, ground subsidence hazards also occur where evaporitic bedrock (gypsum, anhydrite, and rock salt) dissolves. Subsidence sags and ground downwarping, caverns and opens fissures, ground seepage and streams flowing from bedrock, and various types of sinkholes, are landforms collectively called karst morphology. Figure 3-42 shows a comprehensive look at subsidence and collapsible soils in Colorado. Colorado Natural Hazards Mitigation Plan 3 142

143 Figure 3 42: Subsidence Areas in Colorado The Colorado Geological Survey has a series of maps available showing the extent of coal mining in communities along the Front Range. Figure 3-43 provides examples of these maps from Boulder and Huerfano County. They gray areas on the maps indicate the location of undermined land. Additional maps showing the geographic extent of this hazard are included in the future probability discussion below. Colorado Natural Hazards Mitigation Plan 3 143

144 Figure 3 43: Example of County Level Undermined Land Maps Previous Occurrence Occurrences of subsiding and collapsing soils date back to Colorado s early history throughout the locations with natural or human-caused characteristics that make it prone to this hazard. Undermined One evening in 1974 a Lafayette, Colorado, trailer park resident noticed a two-foot hole in his front yard. By morning the hole was 10 feet deep and 10 feet across. The trailer was moved as the hole continued to grow until it was about 25 feet deep and 25 feet in diameter. The sidewalk, a telephone pole, a concrete pad and a fence had to be replaced after the hole was filled. Fortunately a gas line exposed by subsidence did not rupture. The property owner backfilled the hole, acknowledging the site had previously subsided and had been filled. An inclined shaft to an old coal mine underlies the site. The workings were abandoned more than 50 years ago. Interstate Highway 25 crosses several abandoned coal mines in Weld County. Roadway settlement of more than two feet near Erie has taken place in patterns that can be closely correlated to subsidence over coal mine workings 350 to 400 feet below the surface. Much of the severely damaged road is now below original grade, resulting in a mild roller coaster like ride. Estimates for repair of the ¾ mile section damaged by subsidence are about $1 million. Friday, April 13, 1979, was a lucky day for a group of Colorado Highway Department workers and passersby. Maintenance crews found a 500 foot deep airshaft to the abandoned Klondike coal mine had been reopened by surface subsidence into the mine. A crater about 20 to 25 feet across opened like a funnel into the shaft just off the pavement Colorado Natural Hazards Mitigation Plan 3 144

145 on the northeast corner of the Interstate-25 Woodmen Road interchange in Colorado Springs. The shaft had previously been capped, but the slow deterioration of the surface plug finally caused this reopening. Collapsible Soils The first settlers of the plateau region of western Colorado along the Colorado River, and the Uncompahgre and Paonia river basins, looked to fruit crops for their livelihood. The semi-arid but moderate climate was well suited for fruit orchards once irrigation canal systems could be constructed. But serious problems occurred when certain lands were first broken out for agriculture and wetted by irrigation. They sank, so much in places (up to 4 feet!) that irrigation-canal flow directions were reversed, ponding occurred, and whole orchards, newly planted with fruit trees imported by rail and wagon at considerable expense, were lost. While not understood, fruit growers and agriculturists began to recognize the hazards of sinking ground. (Colorado Geological Survey) A Carbondale, Colorado, rancher s stock watering pond excavated in a pasture collapsed because of hydrocompaction. A bowl-shaped depression 60 feet across and 8 feet deep resulted when he attempted to pond water in his field. The soils were so permeable that the pond would not hold water, and the wetted soils under the pond collapsed. Many roads and other improvements in the vicinity have been destroyed or damaged by soaking of collapsible, low density soils. The Colorado Highway Department, recognizing that severe hydrocompaction along a highway alignment could totally destroy a road, investigated the potential for hydrocompaction along the alignment of I-70 from Rifle to Debeque. Water was impounded in a small pond and a road fill was placed beside the pond as a model of probable future conditions. The result of the test was that the ground surface sank three feet in one month. The test provided design information to prevent the possible future total failure of a portion of the highway. The engineering geologic investigation may have saved taxpayers millions of dollars. At Golden, abandoned clay pits were used as a refuse dump. In the 1960 s after the pits were "filled", a residential housing complex was built on sites for the Colorado School of Mines. Sidewalks, streets, and two story buildings have sustained substantial damage from settlement. The problem continues despite repeated repairs and some corrective work. Future Probability Understand the future probability of subsidence and collapsible soil risk is largely dependant on understanding the locations susceptible to the hazard. Colorado Natural Hazards Mitigation Plan 3 145

146 Undermined Many old mines are located near present urban areas. With Colorado s population growth in the last 25 years, not only have many homes been built over abandoned mines, but many homeowners are unaware of previous mining or the extent of mining in an area. A name such as Coal Mine Avenue may seem fanciful rather than significant. Subsidence over abandoned coal mines is a potential hazard for thousands of homes along the Front Range Urban Corridor, and these numbers will continue to grow as more people move into the state. Figure 3-44 indicates general locations of inactive coal mines throughout the state. Figure 3 44: General Locations of Inactive Coal Mines in Colorado Source: Colorado Geological Survey A residence or other structure may be subject to subsidence if it is located over or close to an undermined area. Therefore, the first step in determining the subsidence potential at a specific location is to discover if the area is undermined. Some recent housing developments in the Front Range Urban Corridor, in response to Senate Bill 35 (1972), have had subsidence hazard investigations completed prior to development. Individual site-specific investigations involve examining the available data Colorado Natural Hazards Mitigation Plan 3 146

147 and drilling exploratory holes for information on the present condition of the mine. These investigations are completed to determine how the subsidence hazard can affect proposed development, if safe building areas exist, and what areas should be avoided. These studies, when available, are often on file with the builder, city, or county. They also may be available for inspection from the files of the Colorado Geological Survey. Evaporative Karst Subsidence As shown in Figure 3-45, the highest densities of surface sinkholes in Colorado occur in the Roaring Fork River-Carbondale area in Garfield County, the Eagle River around Gypsum and Edwards in Eagle County, the Buford-North Fork White River area in Rio Blanco County, and Park County south of Fairplay. Figure 3 45: Evaporative Bedrock Locations in Colorado Source: Colorado Geological Survey Colorado Natural Hazards Mitigation Plan 3 147

148 Collapsible Soils With few exceptions, soil collapse appears to occur in areas that have less than 20 inches of annual precipitation. Therefore their natural state is typically dry. Local ground-water levels generally never rise into these mantles of soil so they never become saturated. Only through human development and land use do local ground-water levels rise. The soils become introduced to moisture, through combinations of field irrigation, lawn and landscaping irrigation, capillary action under impervious slabs, leaking or broken water and sewer utilities, and altered drainage. Figure 3-46 shows the combination of high precipitation and historic case studies that may result in favorable environments for collapsible soils. Figure 3 46: Collapsible Soil Case Histories in Colorado Source: Colorado Geological Survey Colorado Natural Hazards Mitigation Plan 3 148

149 Magnitude and Severity Subsidence can result in serious structural damage to buildings, roads, irrigation ditches, underground utilities and pipelines. It can disrupt and alter the flow of surface or underground water. Surface depressions created by subsidence may be filled in, only to sink further because the underground void has not been completely closed. Areas may appear to be free of subsidence for many years and then undergo renewed gradual or even drastic subsidence. The large ground displacements caused by collapsing soils can totally destroy roads and structures and alter surface drainage. Minor cracking and distress may result as the improvements respond to small adjustments in the ground beneath them. FEMA estimates annual losses in US at over $125 million. Most homeowners insurance policies specifically exclude subsidence events. Over 1,000 participants are currently enrolled in the Mine Subsidence Protection Program in Colorado. This program was set up to pay for damage to homes resulting from subsidence due to coal mining. Geologic conditions conducive to subsidence are extensive throughout Colorado. Known serious problems of mining related subsidence, hydro-compaction, and dissolution subsidence are known to occur in the state. With increased demand for mineral fuels, other mining activities and pressures for intensive urban and recreational development throughout much of the state, these problems will intensify unless recognized and wisely dealt with. Sources Colorado Geological Survey (CGS) Federal Emergency Management Agency (FEMA) Colorado Natural Hazards Mitigation Plan 3 149

150 Other Fire Grasshopper Infestation Colorado Natural Hazards Mitigation Plan 3 150

151 Fire Information provided in this profile is collected from the Colorado State Forest Service (CSFS) and the associated efforts put forth regarding forest management and fire mitigation. Additional information may be found in the attached Wildfire Hazard Mitigation Annex. Hazard Analysis Summary Consideration Impact Description Geographic Location Statewide Grassland and forest fires occur throughout the state. Eastern plains, Front Range foothills, and the West Slope all have high to moderate wildfire risk. Every county has some area determined at least a moderate risk. Previous Occurrences Perennial Regular occurrences throughout the fire season from March to August, but forest and grass fires are a year round occurrence. Human caused or natural in origin. An annual average of 2,164 wildfires occurs on state and private lands. Future Probability Expected Events producing conditions prone to wildfires are expected to occur as in the past. These conditions are variable based on precipitation, drought, fuel loading, lightning strikes, and other human activities. Magnitude/Severity Extensive Major or long term property damage that threatens structural stability, isolated deaths (average 1 every 2 years) and injuries, impact to critical lifelines, potential impact to government s ability to provide service. Definition Wildland Fire is defined as an unplanned, unwanted wildland fire including unauthorized human-caused fires, escaped wildland fire use events, escaped prescribed fire projects, and all other wildland fires where the objective is to put the fire out. Wildfires are divided into four categories: Wildland fire fuel consists mainly of natural vegetation Interface or intermix fire urban/wildland fires that consist of vegetation and manmade fuel Catastrophic Fire a very intense event that makes suppression very difficult and negatively impacts human values. Prescribed fire Any fire ignited by management actions to meet specific objectives. A written, approved prescribed fire plan must exist, and National Environmental Policy Act programmatic agreement requirements (where applicable) must be met, prior to ignition. Colorado Natural Hazards Mitigation Plan 3 151

152 Characteristics Three main factors influence wildfire behavior topography, fuel, and weather. Other hazards can contribute to the potential for wildfires or can influence wildfire behavior. High winds can down power lines; earthquakes can crack gas lines; lightning can spark fires. Lightning is a major cause of structural fires and wildfires. In 1997, a lightning-caused warehouse fire in Denver resulted in a $70 million loss. Drought conditions increase wildfire potential by decreasing fuel moisture. Warm winters, hot, dry summers, severe drought, insect and disease infestations, years of fire suppression, and growth in the wildland-urban interface continue to increase wildfire risk and the potential for catastrophic wildland fires in Colorado. Forest insect epidemics and forest parasites contribute to wildfire potential by increasing fuel loading. Over the past two decades, Colorado has experienced an increase in insect infestations that have left vast areas of forest vulnerable to wildfire. These infestations, coupled with the increasing number of people who live in the wildland-urban interface, where humans and human-made structures abut vegetation, make Colorado increasingly susceptible to large-scale fires that threaten human lives, communities, power lines, roads, domestic water supplies, wildlife habitat, and other important resources. Protecting the wildland-urban interface is the nation s fastest-growing firefighting expense. In 2007, suppressing wildfires in the WUI accounted for 85 percent of firefighting costs in the United States. Protecting life and property in these areas is costly because fire managers must take an aggressive stand on the ground and from the air. Geographic Location The threat of wildfires is statewide in Colorado with the forests, grasslands, and wildland/urban interfaces all at risk. Figure 3-47 shows statewide land cover data showing the distribution of forested, shrub/scrub, and grasslands areas throughout the state. Agricultural areas, which are also at risk from wildfire, are identified in the map as well. Colorado Natural Hazards Mitigation Plan 3 152

153 Figure 3 47: Colorado Land Cover Previous Occurrences Table 3-48 presents a list of the more significant wildfire events in Colorado. The attached wildfire support document provides additional historic accounts of wildfire activity by year dating to The locations below reinforce wildfire as a statewide hazard. Colorado Natural Hazards Mitigation Plan 3 153

154 Table 3 48: Notable Fire Events in Colorado, 1938 to 2010 Year Location/Name Costs/Losses 1937 Roosevelt NF 1 death 1976 Battlement Mesa, Grand Junction 3 deaths, 880 acres 1985 Columbia 1 death 1986 Montrose 4 deaths 1988 Lefthand Canyon, Boulder Co. 2,500 acres 1989 Black Tiger, Boulder Co. $10,000,000, 44 structures, 1,778 acres 1989 Panorama, Garfield & Eagle Counties Unknown 1990 Olde Stage, Boulder Co. 10 structures, 3,000 acres 1991 Routt NF 1 death 1992 Glenwood Springs 1 death 1994 Hourglass (Pingree Park) 13 structures, $2,200, Wake, Delta Co. $2,675,000, 3 structures, 4,000 acres 1994 South Canyon, Garfield Co. 14 deaths, 2,115 acres 1994 Roxborough, Jefferson Co. 100 acres 1996 Buffalo Creek, Jefferson Co. $3,835,000, 10 structures, 12,000 acres 1999 Battlement Mesa 9 structures 2000 Eldorado, Boulder Co. $2,000, Bobcat, Larimer Co. 18 structures, 10,600 acres 2000 Hi Meadow, Jefferson Co. 51 structures, 10,800 acres 2000 Pony Fire 4 structures, 5,240 acres 2000 Eldorado Fire Walker Ranch 1,061 acres 2000 Bircher (Mesa Verde) 19,709 acres 2001 Larkspur 1 death 2001 Armageddon Carter Lake 1,216 acres 2002 Snaking Fire 2,590 acres, 2 structures 2002 Cuerno Verde Fire 388 acres, 2 structures, 2 deaths 2002 Black Mountain Fire 200 acres, 1 injury 2002 Schoonover Fire 3,862 acres, 12 structures, 1 bridge, 2 injuries 2002 Iron Mountain Fire 4,440 acres, 200+ structures, 3 injuries 2002 Spring & James John/Fisher (Trinidad Complex) 17,295 acres, 6 injuries 2002 Ute Pass Fire 2002 Coal Seam Fire 12,209 acres, 99 structures & 14 outbuildings 2002 Hayman Fire 137,760 acres, 5 deaths, 16 injuries, 600 structures 2002 Dierich Creek/Long Canyon (Miracle Complex) 3,951 acres, 1 injury 2002 Missionary Ridge Fire 70,485 acres, 56 structures, 52 injuries, 1 death 2002 Million Fire 9,346 acres, 11 structures Colorado Natural Hazards Mitigation Plan 3 154

155 Year Location/Name Costs/Losses 2002 Mt. Zirkel Complex 31,016 acres 2002 Wiley Ridge Fire 1,084.5 acres 2002 Valley Fire 400 acres, a few homes 2002 Burn Canyon Fire 31,300 acres, 9 injuries 2002 Big Elk Fire 4,413 acres, 1 air tanker, 3 deaths 2002 Big Fish 17,056 acres, 1 lodge, 7 cabins 2002 Long Mesa 2,601 acres, 3 homes 2002 Panorama Fire 1,700 acres, 4 homes 2003 Brush Mountain 5,292 acres 2003 Overland 3,439 acres, 12 homes 2003 Cherokee Fire 1,200 acres, 2 homes 2004 Picnic Rock 8,908 acres, 1 home 2005 Mason 11,357 acres 2006 Mauricio Canyon 3,825 acres 2006 Yuma County 23,000 acres 2006 Thomas 3,347 acres 2006 Mato Vega 13,820 acres 2007 Newcastle 1420 acres 2007 Bear 1526 acres, 1 home, 2 structures 2007 Wolf Park 150 acres 2007 Holms Mesa 180 acres 2008 Ordway 8900 acres, 14 homes, 10 structures, 3 Fatalities 2008 Incline 30 acres 2008 Bridger 45,800 acres 2008 Nash Ranch 1115 acres, 2 structures 2008 Ferguson 190 acres 2008 Housetop 143 acres 2009 Olde Stage 1300 acres, 3 homes, 2 structures 2009 Newlin Creek 142 acres 2009 Grammar 801 acres 2009 Spring Creek 1,340 acres 2010 Parkdale 628 acres, 1 home, 1 structure 2010 Fourmile Canyon 6280 acres, 169 homes, 5+ structures 2010 Reservoir Road 710 acres, 2 homes, 3 structures Sources: Teie & Weatherford 2000, Wildfire Hazard Mitigation Plan 2007, CSFS 2009 Fire Report Colorado Natural Hazards Mitigation Plan 3 155

156 Case Studies The timing and location of the Hayman Fire coincided with fire prone conditions in Colorado. In 2002, much of the Front Range of the Rocky Mountains in Colorado was rich in dry vegetation as a result of fire exclusion and the drought conditions that prevailed in previous years. The dry and heavy fuel loadings were continuous along the South Platte River corridor located between Denver and Colorado Springs on the Front Range. These topographic and fuel conditions combined with a dry and windy weather system centered over eastern Washington to produce ideal burning conditions. The Hayman Fire had a wildfire run in 1 day of over 60,000 acres and finally impacted over 138,000 acres. This represents Colorado s largest wildland fire in terms of acres burned. The Fourmile Canyon fire started in Boulder County on Labor Day The resulting event burned nearly 6280 acres, 169 homes, and many other structures and quickly became Colorado s most costly wildland fire relative to home and property value lost. Early estimates on insured property losses for this fire are around $200 million. In addition to property losses, many residents in the area were displaced for a week. Those who did not evacuate lacked access to water and electric service. Future Probability The CSFS has conducted several assessments that address wildfire hazard and risk. The assessments took place in 1999, 2002, and While slightly different methodologies were used in each assessment, the outcomes show very similar areas are susceptible to wildland fire in the terms of risk and hazard. Table 3-49 reflects the risk assessment from 1999 known as the mid-level assessment. Jefferson County has the highest percentage of area at risk with 57 percent, followed by several in the 30 percent ranges including Douglas, Fremont, Garfield, and Teller. Counties in the 20 percent range at risk from wildfire include Archuleta, Clear Creek, Delta, Eagle, Gilpin, Gunnison, La Plata, Larimer, Mesa, Montrose, Ourey, Pitkin, and San Miguel. Colorado Natural Hazards Mitigation Plan 3 156

157 Table 3 49: Colorado Counties by Percent of Acres at Risk for Wildfire: 1999* County Percent of Area at Risk Moderate to High Hazard (acres) Total Acres Adams , Alamosa , , Arapahoe , , Archuleta , , Baca Bent Boulder , , Broomfield Chaffee , , Cheyenne Clear Creek , , Conejos , , Costilla , , Crowley Custer , , Delta , , Denver , Dolores , , Douglas , , Eagle , ,088, Elbert , ,182, El Paso , ,362, Fremont , , Garfield , ,892, Gilpin , , Grand , ,196, Gunnison , ,084, Hinsdale , , Huerfano , ,019, Jackson , ,036, Jefferson , , Kiowa Kit Carson Lake , , La Plata , ,088, Larimer , ,684, Las Animas , ,053, Lincoln Logan Colorado Natural Hazards Mitigation Plan 3 157

158 County Percent of Area at Risk Moderate to High Hazard (acres) Total Acres Mesa , ,141, Mineral , , Moffat , ,042, Montezuma , ,303, Montrose , ,437, Morgan Otero Ouray , , Park , ,414, Phillips Pitkin , , Prowers Pueblo , ,534, Rio Blanco , ,065, Rio Grande , , Routt , ,511, Saguache , ,027, San Juan , San Miguel , , Sedgwick Summit , , Teller , , Washington Weld , ,570, Yuma Based on the Mid level wildfire assessment, March 1999 by the Colorado State Forest Service and Office of Emergency Management The second risk assessment was completed in 2002 by the Colorado State Forest Service. Full details of the risk assessment, including the methodology and digital layers used, are included in attached wildfire supporting document. Figure 3-48 was generated as a product of this assessment and indicates the wildland urban interface hazard assessment for the state. This map shows that every county has some area with at least a moderate interface wildfire hazard. Colorado Natural Hazards Mitigation Plan 3 158

159 Figure 3 48: Colorado Wildland Urban Interface Hazard Assessment Potential losses to wildfire were estimated by intersecting the high risk zones (values 10-15) from the 2002 hazard assessment with the building and contents values provided in the HAZUS-MH loss estimation software. The analysis was completed at the census block level then summarized by county. If a high risk zone intersected only part of any given census block, the area ratio was used to calculate the building and contents values assuming an equal distribution. While every county in the state has the potential for loss, Jefferson ($8.9 billion), Boulder ($6 billion), Douglas ($5.4 billion), El Paso ($5.4 billion), and Larimer ($4.1 billion) have the greatest potential for dollar losses in high risk zones. The third assessment was completed in the fall of 2008 and is reflected in Figure This assessment focused on the susceptibility of wildfire risk in the western two thirds of Colorado. The eastern plains were not included in the assessment because national fuel typing had not been completed at the time of the assessment. CSFS with the assistance of the Division of Emergency Management cost share grant plans to complete an eastern plains assessment in early Colorado Natural Hazards Mitigation Plan 3 159

160 The 2008 Wildfire Risk Assessment brought together the elements of fire occurrence, weather influence zones, and national standardized fuel models adjusted and groundtruthed for Colorado. CSFS purchased license to the software developed for the assessment and will be able to update the assessment as new data is received. CSFS printed and distributed county susceptibility maps to each county in the assessment area. Figure 3 49: Colorado Wildfire Risk Assessment 2008 Magnitude and Severity Wildfires play a significant role in the development of Colorado s diverse ecosystems. Through time, wildfires have been both beneficial and destructive. That relationship is measured, in part, by the number and frequency of wildfires, how they were ignited, the cost of suppression, and the dollar value of what was burned, the negative impact on the environment and the related costs to infrastructure, air and water quality, and human values/benefits. Wildfires have post fire impacts that may contribute to the susceptibility of mudslides, landslides, and floods in areas where fire has burned off vegetation. In recent years, Colorado Natural Hazards Mitigation Plan 3 160

161 roads, residential structures and outbuildings have suffered prolonged damaging impacts from flood, mudslides, and siltation of municipal water sources in areas scarred by wildfires. Large fire incidents, such as the Hayman Fire, can leave critical watersheds in need of emergency and long-term rehabilitation. Since 2002, Denver Water has spent millions to restore Strontia Springs Reservoir, which was severely impacted by runoff caused by the Hayman Fire. The 2002 Colorado wildfire season was the most expensive in the state s recorded history. The overall estimated cost of insured losses related to the Iron Mountain, Coal Seam, Missionary Ridge and Hayman Fires is $70.3 million ($78.8 million in 2006 dollars). Insurance companies paid an estimated $56.4 million for 1,236 claims related to the Hayman and Missionary Ridge fires alone. Table 3-50 shows building and content value exposed to high risk wildfire zones by county. Table 3 50: Building and Contents Values in High Risk Wildfire Zones County Exposure ($000s) County Exposure ($000s) Adams $1,472,568 La Plata $1,464,219 Alamosa $113,532 Lake $51,543 Arapahoe $1,794,503 Larimer $4,136,945 Archuleta $628,988 Las Animas $248,457 Baca $128,792 Lincoln $125,561 Bent $2,539 Logan $506,894 Boulder $6,032,590 Mesa $652,620 Chaffee $346,101 Mineral $82,619 Cheyenne $87,084 Moffat $81,019 Clear Creek $852,894 Montezuma $209,672 Conejos $73,938 Montrose $355,534 Costilla $30,023 Morgan $3,243,694 Crowley $150,490 Otero $238,909 Custer $174,350 Ouray $96,028 Delta $544,192 Park $891,563 Denver $102,710 Phillips $108,235 Dolores $47,517 Pitki $748,445 Douglas $5,445,250 Prowers $192,966 Eagle $1,742,943 Pueblo $289,553 El Paso $5,424,875 Rio Blanco $60,842 Elbert $1,067,531 Rio Grande $156,854 Fremont $261,257 Routt $764,981 Garfield $935,392 Saguache $40,381 Gilpin $319,242 San Juan $28,952 Grand $790,525 San Miguel $318,370 Colorado Natural Hazards Mitigation Plan 3 161

162 County Exposure ($000s) County Exposure ($000s) Gunnison $424,010 Sedgwick $46,399 Hinsdale $92,915 Summit $1,223,161 Huerfano $50,090 Teller $1,145,128 Jackson $8,855 Washington $60,949 Jefferson $8,937,700 Weld $2,351,598 Kiowa $9,782 Yuma $208,443 Kit Carson $213,296 Total $58,437,008 *Sources: CSFS 2002 WUI Hazard Assessment, Hazus Mr2 Sources Colorado State Forest Service (CSFS) Teie, W. C., and B. F. Weatherford Fire in the West: The wildland/urban interface fire problem. Report to the Council of Western State Foresters. Rescue, CA: Deer Valley Press. United States Department of Agriculture, Forest Service HAZUS Colorado Natural Hazards Mitigation Plan 3 162

163 Grasshopper Infestation Hazard Analysis Summary Consideration Impact Description Geographic Location Regional Eastern plains are most impacted area coinciding with rangeland. Portions of western Colorado are also impacted but to a lesser extent. Higher elevations are largely void of significant grasshopper populations. Previous Occurrences Cyclical Outbreaks occur cyclically and may be encouraged by drought conditions. In addition, populations may increase as grazing rates increase. In 2009, northeast experienced the highest grasshopper infestation since Future Probability Sporadic Natural and human induced conditions responsible for past outbreaks are expected to continue. Weather conditions have high impact on outbreak potential. Magnitude/Severity Moderate Limited or short term property damage; no deaths or few injuries; little or no impact on critical services or facilities. Damage to rangeland and crops may be severe enough to warrant USDA disaster or emergency declarations. Damage depends on where grasshopper outbreaks originate and where they migrate to. Definition A grasshopper infestation or outbreak may simply be defined as a swarm of insects that attack plants. Although grasshoppers feed on range and cropland on an annual basis, infestation or outbreak applies to extraordinary numbers of insects causing economic hardship to ranchers or farmers. Characteristics Grasshoppers are an important native component of grassland ecosystems in the United States, playing a role in nutrient cycling and serving as a critical food supply for wildlife. However, in large numbers grasshoppers become undesirable pests. They follow a roughly 22-year cycle in Colorado. The last major outbreak was in the late 1970s and early 1980s with a recent recurrence in 2009 and However, crop or rangeland damage occurs even in years of low numbers. Grasshoppers are chewing insects that feed from the outer edges of leaves inward. When numerous on corn, they even eat part of the stalk and ears. They attack fresh silks, reducing pollination and often causing the ears to be blank or only partly filled. Even light infestations of 6 or 7 grasshoppers per square yard in a 10-acre hay field will eat as much hay as a cow; 17 hoppers per square yard in a 40-acre hay field will eat a ton of hay Colorado Natural Hazards Mitigation Plan 3 163

164 a day. All types of field crops, vegetable crops, fruit crops, flowers, and shrubs are subject to attack. Grasshoppers lay eggs in undisturbed areas, usually in late summer and early fall. Small nymphs or "hoppers" hatch the following spring. Winged adults appear five to six weeks after hatch. Eggs of a few Colorado species hatch in late summer and pass the winter as nymphs. Winged adults of these species usually appear early in the following summer, often causing undue alarm about unusually early grasshopper activity. Some of these early-season species are important on rangeland, but none are considered a threat to field Crops. Most field crop damage is caused by the differential, redlegged, two-striped and migratory grasshoppers, all species that follow the typical grasshopper life cycle. Geographic Location The eastern plains of Colorado are most typically impacted by grasshopper infestations as the area coincides with rangeland. Western Colorado is also impacted but to a lesser extent. Higher elevations are largely void of significant grasshopper populations. Figure 3-50 shows the results from a 2009 survey of adult grasshoppers in the Western United States. High adult counts in one year will typically suggest a perpetuation of high numbers the following year. Generally, the eastern plains and northwest Colorado show the highest numbers of adults, largely in the 3-8 adults per square yard. Some isolated areas in Colorado have showed more than 15 adult grasshoppers per square yard. Colorado Natural Hazards Mitigation Plan 3 164

165 Figure 3 50: Rangeland Grasshopper Hazard in the Western United States Previous Occurrences Grasshopper infestations vary in their intensity from year to year. Generally speaking, seasons that have large populations will occur for two to four years simultaneously. After this cycle a period of low infestation will happen for three to four years. The cycles often repeat in this manner. Adults live for approximately 60 to 90 days. Outbreaks occur cyclically and may be encouraged by drought conditions. In addition, populations may increase as grazing rates increase. In 2009, northeast Colorado experienced the most significant grasshopper infestation since In 2003, 2005, and 2006, a number of eastern Colorado counties received a United States Department of Colorado Natural Hazards Mitigation Plan 3 165

166 Agriculture (USDA) Secretarial Disaster declarations related to insect infestations/insect pests. Future Probability Natural and human-induced conditions responsible for past outbreaks are expected to continue. Weather conditions have high impact on outbreak potential. Magnitude and Severity While grasshoppers are natural components of the rangeland ecosystem, their populations can reach outbreak levels and cause serious economic losses, especially when accompanied by a drought. Both rangeland forage and cultivated crops can be destroyed by grasshoppers; the damage depends on where the grasshopper populations originate and where the grasshoppers move to. Many grasshopper outbreaks that originate on rangeland can move into and destroy crops such as alfalfa, wheat, barley, and corn. Grasshopper infestations may destroy 80 percent or more of the forage in areas as large as 2,000 square miles, forcing producers to purchase hay and other feed much earlier than in most years. It has been estimated that grasshoppers annually destroy on average at least 21 to 23% of available range forage in the western United States. In response, some producers may sell their livestock early or cease grazing altogether. This damage to rangeland and crops may be severe enough to warrant USDA disaster or emergency declarations. The simple economic threshold for grasshoppers in rangeland is grasshopper nymphs per square yard. This number is equivalent to eight to ten adult grasshoppers per square yard. However, the economic importance of an infestation is affected by such factors as range condition, cattle prices, and treatment costs. Sources United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS) Colorado State University Extension Integrated Pest Management Website Colorado Natural Hazards Mitigation Plan 3 166

167 Vulnerability Requirement 201.4(c)(2)(ii): [The State risk assessment shall include an] overview and analysis of the State s vulnerability to the hazards described in this paragraph (c)(2), based on estimates provided in local risk assessments as well as the State risk assessment. The State shall describe vulnerability in terms of the jurisdictions most threatened by the identified hazards, and most vulnerable to damage and loss associated with hazard events. State owned critical or operated facilities located in the identified hazard areas shall also be addressed. The HIRA is a process developed to provide an overview and analysis of the state s vulnerability to hazards. This assessment is performed to identify Colorado s vulnerability to the people, property, environment, infrastructure, and services that are likely to be negatively impacted by a natural hazard. Vulnerability should consider all people in an area impacted by a natural hazard including first responders, workers, commuters, visitors, residents, and tourists. Populations with special needs such as hospital patients, prison inmates, or areas with large non-english-speaking populations also need to be considered because they can be more vulnerable to hazard events. Additional understanding of vulnerability is determined through an inventory of the built environment including the number of buildings, their value, and their purpose and/or occupancy. The major assessment components of the HIRA include data and information from: The Colorado Overview section of the State Plan Colorado Office of Risk Management County-level building and content value from HAZUS Total population and population change by county is addressed in the Colorado Overview section, as well as in regional profiles in Appendix C. Population data and the regional profiles are provided by the Colorado Demography Office. State owned and operated critical facilities and lands not included in this analysis will be evaluated and considered for independent analysis during the next planning process. The exposure and loss estimates of state owned assets was comprehensive in that critical facilities were included into the overall asset database and not evaluated as a separate group. In addition, state-owned lands were evaluated in the flood and drought annexes but not yet into the overall all-hazard risk assessment in the State Plan. Primary areas of consideration within this vulnerability analysis in this plan are listed below: State Asset Exposure Local Jurisdictions Future Development Colorado Natural Hazards Mitigation Plan 3 167

168 State Asset Exposure State of Colorado Organizational Structure Oversight for assets belonging to the State of Colorado reflects the overall organization of state government. Colorado is organized into the three (3) branches of state government: Legislative, Executive, and Judicial. The Legislative Branch oversees the Senate and House of Representatives in the State Capitol Building as is responsible for the content value located in five (5) state assets. The asset value of building contents for this branch is $5,933,703. The state capitol building is the responsibility of the Department of Personnel and Administration. The Judicial Branch is responsible for the State Supreme Court, state district and county trial courts, appeals court, and probation services. This branch is responsible for building or content value of six (6) facilities with a combined building and/or content value of $66,104,649. The Executive Branch is organized into five (5) elected offices and sixteen (16) departments, which the Governor oversees. This branch is responsible for the bulk of state asset building and content value with 7,562 of total state assets evaluated in the State Plan with a value of nearly $18 billion. Definition of State Asset for Planning Purposes The bulk of asset analysis in the Colorado Pre-Disaster Mitigation Plan is focused on a database of insured state assets from the Colorado Office of Risk Management (ORM). The ORM database is comprised of agency reported business or infrastructure locations with building and content value. Also included are building leases where there is only content value reported. Other data sources providing assets included the Offices of Risk Management at the University of Northern Colorado, the University of Colorado system, and the Colorado State University system. The attached flood and drought mitigation plans go further into state asset analysis by looking at impacts to managed state land (land board, parks, wildlife areas, fisheries, etc.) with associated revenue and tourism considerations. Insured State Assets As shown in Table 3-51, between the 2007 and 2010 State Plan updates, the number of evaluated state assets increased from 7,154 to 7,573, or by nearly 6 percent. This increase in the number of assets included in the analysis is a result of a greater number of records included in the overall state asset database and enhanced georeferencing performed on the 2010 records. This enhanced georeferencing, or identifying the geographic location of the asset, allowed for enhanced analysis of assets falling into the geographic extent of natural hazards in the state in terms of total counts and value. Colorado Natural Hazards Mitigation Plan 3 168

169 More significant than the increased number of assets included between 2007 and 2010 is the increase in reported asset value. During this period, the total building and content value reported by state agencies for the assets increased from $13 billion to nearly $18 billion, or an increase of 38 percent. Table 3 51: State Asset Count and Value, 2007 and 2010 Asset Total Change Percent Change Count 7,573 7, % Value $17,998,087,774 $13,030,331,107 $4,967,756,667 38% Source: Office of Risk Management, State University System The State of Colorado owned 86 percent of assets evaluated in the 2010 State Plan update as shown in Table The reported ownership rate of assets is up from 83 percent in 2007, the difference resulting largely from the inclusion of numerous smaller state-owned assets in Table 3 52: State Asset Ownership, 2010 Ownership Asset Count Percent Owned 6,503 86% Leased/Unknown 1,070 14% Total 7, % Source: Office of Risk Management; State University System State Assets by Agency Standing out as primary agencies for the oversight of state assets is the Department of Corrections, Higher Education, Transportation, Human Services, and Natural Resources. These five (5) agencies account for 6,789 of the 7,573 state assets assessed in this plan, or 89.6 percent of the total number. The assets these agencies oversee represent 92 percent of the value of total state assets. Table 3 53: Asset Overview for Primary State Asset Holders Department Corrections Asset Overview Administrative buildings, living units, gyms, clinics, vocational shops, gate house, water towers, warehouses, industrial facilities, water tanks, parole offices, utilities (wastewater treatment, boiler rooms, pump houses, chiller plants), gas stations. Colorado Natural Hazards Mitigation Plan 3 169

170 Department Higher Education Human Services Natural Resources Transportation Asset Overview Administrative buildings, student housing (dorms, apartments, houses), classroom buildings, laboratories, recreation centers, sports facilities, event centers, utilities, bookstores, printing centers, parking garages, libraries, student centers, medical clinics, theaters, warehouses, child care facilities, agricultural facilities, vehicle support (fueling, maintenance, storage). Administrative offices, mental health institutes, gyms, learning centers, group homes, client housing, nursing homes, utilities (heating/power plants, pump house) warehousing, schools, garages, veteran s homes. Weather stations, employee housing, offices, agricultural buildings, warehousing and storage sheds, cabins, restrooms, visitor centers, shower and laundry facilities, picnic shelters, boat storage and docks, playgrounds, vehicle support (fueling, maintenance, garages). Administrative and regional offices, tunnel infrastructure and control, warehousing, vehicle maintenance garages, sand and salt sheds, fueling stations, rest areas (picnic shelters, restrooms), employee housing. Source: Colorado Office of Risk Management The Department of Higher Education, representing the State s university and community college system, is responsible for 71.5 percent of the value of all state assets with $12.8 billion. With a total of 2,313 assets, or 30.5 percent of the total count, the Department of Natural Resources is responsible for the greatest number of physical assets of any state agency. Table 3-54 shows additional information on assets by state agency. Table 3 54: State of Colorado State Assets by Agency, 2010 Organization Asset Count Percent of Total Assets Asset Value Percent of Total Value Agriculture % $90,464, % Corrections % $1,413,308, % Education % $68,906, % Personnel & Administration % $594,187, % Health Care Policy 2 0.0% $4,055, % Higher Education* 2, % $12,862,844, % Human Services % $778,929, % Judicial 6 0.1% $66,104, % Labor & Employment % $46,417, % Attorney General 1 0.0% $5,716, % Legislature 5 0.1% $5,933, % Local Affairs 9 0.1% $5,285, % Military Affairs % $121,968, % Natural Resources 2, % $423,491, % Office of Governor % $86,366, % Colorado Natural Hazards Mitigation Plan 3 170

171 Public Health % $56,820, % Public Safety % $99,072, % Regulatory Agencies % $21,541, % Revenue % $71,423, % Secretary of State 1 0.0% $7,847, % Transportation 1, % $1,167,212, % Treasury 2 0.0% $190, % Total 7, % $17,998,087, % Higher Education Breakout* Asset Count Percent of Total Assets Asset Value Percent of Total Value Higher Education (Other) % $4,390,225, % Colorado State University % $2,388,007, % University of Colorado % $3,729,768, % University Health Sciences Center % $1,919,792, % University of Northern Colorado % $643,312, % Sub Total % $13,071,107, % Source: Colorado Office of Risk Management Between 2010 and 2007, there are some significant differences between the count and value of assets some agencies are responsible for: The Office of Information Technology moved from the Department of Personnel and Administration to the Governor s Office. Increase in asset value for the Department of Military Affairs has accounted for a significant increase in reported asset content value. The increase in value of Judicial Branch assets is a result of a 2007 entry error that suppressed total value. The decrease in value of Department of Labor and Employment total value is the result of a 2007 entry error artificially increasing the value. Addition changes in department by department asset count and total value is generally accounted for by changes in reporting methodology, additional assets included in the 2010 database, and increases in building and content value. State Assets by County Distribution of 2010 state assets across Colorado s counties is depicted by total value in Figure Generally, the highest value of state assets is concentrated along the Front Range and across the Grand Valley. Along the Front Range, the far north-central, metropolitan Denver, and south-central counties tend to represent the highest asset values. Colorado Natural Hazards Mitigation Plan 3 171

172 Figure 3 51: State Asset Value by County, 2010 Five (5) counties each contain over $1 Billion in state asset value. These counties include Adams, Boulder, Denver, Jefferson, and Larimer and represent 30 percent of the state s overall asset count and over 60 percent of total asset value. Boulder County holds the highest value of state assets at $3.1 billion, largely due to the high value associated with the University of Colorado campus buildings. Larimer County has the second highest value of state assets with $2.5 billion, again attributable to the value of higher education facilities in this case of Colorado State University. Larimer County also represents the highest total count of state assets with 890, or about 12 percent of total. The City and County of Denver holds the second highest number of assets with 466 and a value of over $1.9 billion which includes many buildings in the State Capitol Complex. Table 3-55 shows a count of state assets with total value by county. Colorado Natural Hazards Mitigation Plan 3 172

173 Table 3 55: Count of State Assets and Total Value by County, 2010 County Asset Count Asset Value County Asset Count Asset Value Adams 211 $2,118,269,699 Kit Carson 27 $2,673,896 Alamosa 116 $346,035,083 La Plata 140 $421,095,847 Arapahoe 203 $409,201,087 Lake 16 $2,155,033 Archuleta 66 $46,124,584 Larimer 890 $2,450,481,699 Baca 10 $1,111,382 Las Animas 99 $174,770,854 Bent 171 $158,574,799 Lincoln 68 $104,741,683 Boulder 278 $3,171,420,967 Logan 167 $239,317,796 Broomfield 13 $1,647,671 Mesa 298 $522,204,237 Chaffee 215 $101,738,348 Mineral 23 $44,789,014 Cheyenne 9 $683,793 Moffat 75 $11,571,657 Clear Creek 67 $63,641,671 Montezuma 77 $18,001,920 Conejos 32 $60,305,220 Montrose 58 $32,364,242 Costilla 25 $1,790,828 Morgan 144 $53,881,133 Crowley 41 $83,745,060 Otero 72 $70,080,178 Custer 4 $1,404,033 Ouray 44 $35,508,450 Delta 114 $36,977,176 Park 80 $11,365,629 Denver 466 $1,922,794,220 Phillips 6 $359,505 Dolores 14 $2,091,105 Pitkin 12 $361,280 Douglas 157 $32,547,496 Prowers 64 $61,123,457 Eagle 134 $16,514,796 Pueblo 394 $809,653,900 El Paso 231 $610,890,696 Rio Blanco 65 $56,520,927 Elbert 12 $2,070,062 Rio Grande 129 $22,124,439 Fremont 328 $613,275,440 Routt 127 $15,533,911 Garfield 226 $510,162,756 Saguache 28 $2,532,510 Gilpin 50 $9,489,227 San Juan 17 $1,512,376 Grand 87 $11,387,239 San Miguel 14 $3,115,032 Gunnison 121 $296,266,401 Sedgwick 31 $2,234,168 Hinsdale 11 $592,778 Summit 49 $233,912,756 Huerfano 63 $30,055,618 Teller 49 $9,779,410 Jackson 63 $7,333,848 Washington 29 $4,150,054 Jefferson 402 $1,216,584,823 Weld 253 $680,990,030 Kiowa 4 $853,672 Yuma 84 $13,599,175 Total 7,573 $17,998,087,774 Source: Office of Risk Management; State University System Colorado Natural Hazards Mitigation Plan 3 173

174 Between 2007 and 2010, some counties show significant differences between the number of assets and the total value of state assets. These differences are largely attributable to the following: An increase in the number of assets in the 2010 database as a result of: o Quality control (addition of existing assets previously overlooked) o New construction Increases in the building and content value as reported by state agencies Improvements in geolocating the assets across the state Changes in asset value for counties with relatively low number of state assets such as Archuleta, Conejos, Custer, Mineral, and Summit stand out when additional assets are assigned to the county or adjustments are made to asset value. In particular, Department of Transportation assets related to tunnel control and infrastructure and other facilities represent tens of millions of dollars in value change for some of these counties. Another significant change in state asset count and value was in Adams County. The buildup of the Anschutz Medical Campus on the site of the old Fitzsimons Army Garrison increased the total value of state assets in the county by $2 billion between 2007 and The Anschutz Medical Campus in Aurora, Colorado is the newest education, research and patient care facility and the largest academic health center between Chicago, Texas and the West Coast. Local Jurisdictions In the State Plan hazard profiles, event occurrences, future probability, and magnitude and severity discussed in local plans were analyzed by region or county where possible. In addition to hazard profiles, local mitigation plans were evaluated to provide insight as to how local jurisdictions view the degree of vulnerability to hazard events. Many plans included planning priorities for the various hazards or provided a risk ranking of high, medium, or low. Analysis entailed the reviews of 28 local mitigation plans. Within the reviewed plans, there was enough detail provided for 52 jurisdictions to include them in the local hazard rankings as presented in the following tables and figures. Table 3-56 provides a summary of prevalent hazards listed as high, medium, or low based on risk assessments by local jurisdictions. There is a significant break between the four top ranked hazards and the remaining hazards. The top four hazards that stand out with respect to high statewide risk rankings are fire, flood, winter storm, and drought. Local jurisdictions tended to consider being at risk to weather-based hazards such as lightning, hailstorms, tornadoes, as medium, along with dam/levee failure, earthquake, and other geologic hazards. A detailed breakdown of rankings by local jurisdiction is provided later in this section in Table Colorado Natural Hazards Mitigation Plan 3 174

175 Table 3 56: Summary of Local Jurisdiction Hazard Vulnerability Rankings Natural Hazard High Medium Low Fire Flood Winter Storm Drought Windstorm Tornado Hailstorm Landslide/Mud/Debris Flow Dam/Levee Lightning Avalanche Earthquake Expansive Soils Extreme Temperatures Subsidence Source: Local Hazard Mitigation Plans The following series of maps show statewide risk of the four highest ranked hazards as provided in local mitigation plans. These hazards are fire (Figure 3-52), flood (Figure 3-53), Winter Storm (Figure 3-54), and Drought (Figure 3-55). The maps represent all 49 counties included in the plans and omit the cities of Boulder, Colorado Springs, and Westminster for presentation purposes. Detailed information on flood and drought is available in the flood and drought plans serving as support documents to the State Plan. Colorado Natural Hazards Mitigation Plan 3 175

176 Figure 3 52: Statewide Fire Risk Ranking Figure 3 53: Statewide Flood Risk Ranking Colorado Natural Hazards Mitigation Plan 3 176

177 Figure 3 54: Statewide Winter Weather Risk Ranking Figure 3 55: Statewide Drought Risk Ranking Colorado Natural Hazards Mitigation Plan 3 177

178 Detailed vulnerability rankings by local jurisdiction are presented in Table Where jurisdictions provided information to directly indicate or derive a high, medium, or low ranking, it is shown in the table as red, orange, and yellow. If a jurisdiction provided an analysis and discussion related to the hazard, but did not include enough information to derive a high, medium, or low ranking, it is represented in the table as blue, or Included in plan. For multi-jurisdictional plans, local jurisdictions were listed out where enough detail was provided to determine the associated risk rankings. This table served as the base for developing the maps presented earlier in this section. Table 3 57: Hazard Risk Ranking by Local Jurisdiction Legend: Information is taken or derived from local hazard mitigation plans. H High M Medium L Low P Included in plan No vulnerability or not analyzed Local Government Avalanche Dam/Levee Drought Earthquake Expansive Soils Extreme Temperatures Fire Flood Hailstorm Landslide/Mud/Debris Flow Lightning Subsidence Tornado Windstorm Winter Storm Adams County H M L H L L M M M M M Alamosa County M H M L M H H L M H M H Arapahoe County H M L H L L M M M M M Boulder County L H H M L L H H L H M M M H H Chaffee County P P P P P P P P P P Cheyenne County L H L L H M M L M L H H H City and County of Broomfield H M L H L L M M M H M City and County of Denver H M L H L L M M M M M City of Boulder L M H M L H H M M L L M H City of Colorado Springs M L L H H L M H M M Clear Creek County H H M H H L H M M M M H Conejos County M L H L H M H L M M H H Costilla County H L H M M L M Custer County P P P P P P P P P P Delta County L M H L L H H M L M H Douglas County H M H H H M H M L M M Eagle County P P P P P El Paso County P P P P P P P Colorado Natural Hazards Mitigation Plan 3 178

179 Legend: Information is taken or derived from local hazard mitigation plans. H High M Medium L Low P Included in plan No vulnerability or not analyzed Local Government Avalanche Dam/Levee Drought Earthquake Expansive Soils Extreme Temperatures Fire Flood Hailstorm Landslide/Mud/Debris Flow Lightning Subsidence Tornado Windstorm Winter Storm Elbert County M M L H H H H H H H Fremont County P P P P P P P P P P Gilpin County M H M H H L M M M M M H Grand County P P P Gunnison County M H M H L H H Hinsdale County M H M H L H H Huerfano County P P P P Jefferson County L H M M M L H H H M M M M M H Kit Carson County M H L L H H M L M L H H H Lake County P P P P P P P P P P Larimer County P P P P P P P P P P P P P P Lincoln County L H M L H H M L M L H H H Logan County M H L L H H M L M L H H H Mesa County M M M M L M H H L H M L L M M Mineral County H L L M H H L M M M M H Montrose County H M M H M H M H M H H Morgan County H H L L H H M L M L H H H Ouray County M H M M L H H M H M M M Park County L L H M L L L L H Phillips County M H L L H H M L M L H H H Pitkin County P P P P P Prowers County P P P P P P P P Pueblo County M L H H M L H M M H Rio Blanco County P P P P P P P P Rio Grande County M L M L H H H M M M M H Routt County L M M L H H M M L L H Saguache County M L H L H M H L M M M M San Miguel County P M P M M P H P H P P P P Colorado Natural Hazards Mitigation Plan 3 179

180 Legend: Information is taken or derived from local hazard mitigation plans. H High M Medium L Low P Included in plan No vulnerability or not analyzed Local Government Avalanche Dam/Levee Drought Earthquake Expansive Soils Extreme Temperatures Fire Flood Hailstorm Landslide/Mud/Debris Flow Lightning Subsidence Tornado Windstorm Winter Storm Sedgwick County M H L L H H M L M L H H H Summit County H M M L H H M M L H Teller County M H M L H M M M M L L H Washington County M H L L H H M L M L H H H Weld County H H L L H H M L M L H H H City of Westminster M M L L L H M M M M Source: Local Hazard Mitigation Plans Detailed discussions of vulnerability and hazard specific information from local plans can be found in the Flood Plan and Drought Plan that serve as supporting documents to the State Plan. In particular, the flood related plan has a roll-up of vulnerability in Section 3.3, Table 7, and the drought related plan includes a similar, but scaled-back discussion in the main body but an extensive analysis as Annex B. Jurisdiction-level information related to the number of persons vulnerable to natural hazards can be found in both the Colorado Overview and Counties and Communities sections of this State Plan. These sections present both total population and population growth by county. In addition to population, countywide building and content value were updated and evaluated to further determine local level vulnerability. There are two county-level output tables provided below: Table 3-58, Total Building and Contents Value (containing the total cost of structures and contents by county) and Table 3-59, Total Building and Contents Values by Occupancy (containing the total cost of structures and contents by county and occupancy). These tables represent local exposure of the built environment by county as included in HAZUS-MH 2007 and 2009 datasets. Colorado Natural Hazards Mitigation Plan 3 180

181 Table 3 58: Local Exposure by County Total Building and Contents Value (000 s) County Total Value Total Value Per Capita County Total Value Total Value Per Capita Adams* $36,628, Kit Carson $854, Alamosa $1,932, La Plata $856, Arapahoe $65,621, Lake $5,528, Archuleta $1,257, Larimer $29,514, Baca $460, Las Animas $1,652, Bent $494, Lincoln $569, Boulder* $42,473, Logan $2,322, Broomfield* $4,760, Mesa $11,708, Chaffee $2,032, Mineral $204, Cheyenne $252, Moffat $1,222, Clear Creek $1,472, Montezuma $2,082, Conejos $620, Montrose $3,469, Costilla $303, Morgan $2,393, Crowley $335, Otero $2,148, Custer $573, Ouray $603, Delta $2,638, Park $2,347, Denver $80,166, Phillips $497, Dolores $209, Pitkin $3,420, Douglas $26,123, Prowers $1,397, Eagle $6,053, Pueblo $14,547, El Paso $2,283, Rio Blanco $836, Elbert $60,076, Rio Grande $1,382, Fremont $3,904, Routt $3,213, Garfield $4,707, Saguache $513, Gilpin $897, San Juan $135, Grand $2,769, San Miguel $1,219, Gunnison $2,341, Sedgwick $363, Hinsdale $240, Summit $5,514, Huerfano $968, Teller $2,776, Jackson $215, Washington $493, Jefferson* $68,597, Weld* $17,820, Kiowa $173, Yuma $1,025, Source: HAZUS 2007 & 2009, Colorado Demography Office *Broomfield represents 2007 data; For 2010 update Adams, Boulder, Jefferson, and Weld Counties totals include Broomfield Colorado Natural Hazards Mitigation Plan 3 181

182 Table 3 59: Local Exposure by County Total Building and Contents Value by Occupancy (000 s) County Residential Commercial Industrial Agriculture Religion Government Education Adams* $25,904,223 $6,741,643 $2,353,604 $306,288 $546,854 $324,936 $451,161 Alamosa $918,532 $796,221 $96,167 $19,178 $29,636 $24,407 $48,421 Arapahoe $46,392,543 $13,812,980 $2,881,397 $206,964 $1,235,238 $352,207 $740,020 Archuleta $897,674 $243,775 $59,937 $8,400 $30,960 $12,193 $4,396 Baca $288,621 $108,318 $7,549 $29,056 $11,296 $3,566 $12,366 Bent $362,906 $59,340 $14,496 $10,652 $18,602 $16,343 $11,810 Boulder* $28,208,496 $9,094,553 $3,329,292 $266,236 $636,108 $231,862 $706,840 Broomfield* $3,457,196 $872,143 $397,532 $11,962 $15,554 $416 $5,656 Chaffee $1,360,291 $459,358 $79,272 $6,948 $65,020 $30,315 $30,805 Cheyenne $154,239 $53,623 $18,534 $12,104 $5,936 $3,274 $4,874 Clear Creek $1,088,816 $240,831 $82,286 $2,598 $25,074 $8,703 $24,364 Conejos $471,917 $76,988 $20,317 $12,868 $7,706 $13,710 $17,460 Costilla $220,551 $37,644 $4,851 $24,796 $5,206 $4,659 $6,038 Crowley $261,852 $37,912 $4,559 $6,234 $9,876 $10,056 $5,042 Custer $427,810 $74,065 $25,357 $6,420 $23,226 $8,150 $8,150 Delta $1,803,961 $462,801 $163,993 $67,920 $70,308 $30,426 $39,038 Denver $48,040,028 $22,219,166 $5,687,378 $166,186 $1,804,348 $986,742 $1,262,412 Dolores $148,032 $24,734 $20,786 $4,278 $4,284 $1,504 $6,064 Douglas $20,054,269 $4,269,227 $973,893 $135,424 $260,314 $82,951 $347,491 Eagle $4,291,329 $1,306,145 $234,679 $40,206 $90,648 $42,581 $47,769 El Paso $1,743,339 $289,830 $115,997 $40,006 $34,018 $23,017 $36,836 Elbert $42,227,939 $11,746,303 $2,928,451 $208,944 $1,466,918 $760,548 $736,992 Fremont $2,766,715 $690,380 $200,827 $26,950 $103,748 $70,856 $44,894 Garfield $3,023,981 $1,130,716 $263,279 $46,104 $105,352 $44,747 $93,634 Gilpin $734,353 $116,167 $22,074 $1,860 $9,582 $8,769 $4,248 Grand $2,203,880 $403,095 $76,708 $10,012 $43,420 $9,774 $22,729 Gunnison $1,639,266 $502,085 $92,680 $15,978 $55,884 $20,070 $15,130 Hinsdale $202,612 $26,576 $3,766 $80 $4,368 $752 $2,388 Huerfano $693,122 $196,870 $25,438 $6,992 $23,828 $6,786 $15,393 Jackson $152,869 $32,111 $10,668 $6,252 $2,436 $8,970 $2,478 Jefferson* $50,926,401 $11,750,522 $3,183,266 $297,652 $1,004,988 $605,994 $828,193 Kiowa $112,222 $25,518 $4,436 $13,154 $4,464 $3,898 $9,560 Kit Carson $464,119 $241,254 $23,176 $53,424 $19,348 $17,788 $35,762 La Plata $586,941 $197,674 $24,333 $1,912 $20,636 $6,640 $18,086 Lake $3,581,445 $1,338,897 $324,654 $41,580 $108,880 $61,224 $71,881 Larimer $20,424,557 $5,953,594 $1,778,149 $216,594 $536,084 $180,226 $425,431 Colorado Natural Hazards Mitigation Plan 3 182

183 County Residential Commercial Industrial Agriculture Religion Government Education Las Animas $1,098,870 $352,388 $80,595 $10,656 $42,606 $26,011 $41,356 Lincoln $381,419 $102,866 $11,213 $19,856 $18,906 $25,477 $9,766 Logan $1,405,558 $483,722 $111,515 $44,934 $60,680 $43,251 $172,868 Mesa $7,630,095 $2,721,900 $752,856 $85,056 $239,090 $119,741 $160,171 Mineral $170,161 $22,670 $5,193 $122 $1,044 $1,456 $3,756 Moffat $834,630 $266,330 $48,504 $13,042 $23,878 $17,165 $19,064 Montezuma $1,303,847 $525,950 $119,798 $20,270 $54,926 $22,161 $35,760 Montrose $2,015,547 $996,861 $227,352 $51,088 $78,982 $49,622 $49,853 Morgan $1,548,876 $523,965 $129,596 $59,138 $61,100 $21,214 $49,990 Otero $1,374,043 $514,664 $67,673 $39,876 $62,032 $23,045 $67,067 Ouray $394,501 $137,564 $35,694 $7,410 $17,144 $4,065 $7,586 Park $2,020,440 $184,207 $71,691 $11,536 $21,236 $21,413 $16,560 Phillips $284,500 $115,466 $26,973 $30,230 $21,450 $7,646 $11,596 Pitkin $2,160,828 $978,470 $102,843 $18,784 $106,286 $20,416 $32,471 Prowers $891,613 $293,320 $76,669 $43,738 $36,184 $23,773 $31,789 Pueblo $9,901,848 $3,221,688 $562,718 $57,316 $444,786 $127,177 $231,962 Rio Blanco $514,186 $164,920 $50,959 $12,664 $18,742 $18,130 $56,504 Rio Grande $865,664 $275,546 $63,338 $79,512 $64,594 $15,107 $18,616 Routt $2,210,750 $722,881 $134,236 $19,262 $52,608 $30,961 $42,972 Saguache $362,104 $78,345 $15,830 $17,362 $18,548 $8,682 $12,606 San Juan $99,141 $25,813 $3,987 $232 $3,544 $1,624 $1,230 San Miguel $866,192 $257,202 $44,376 $7,634 $14,846 $13,971 $15,224 Sedgwick $203,068 $73,198 $20,633 $13,856 $8,258 $38,792 $6,066 Summit $4,457,014 $765,005 $154,425 $15,076 $57,088 $41,486 $24,409 Teller $2,122,756 $413,195 $122,844 $9,202 $48,420 $33,095 $26,898 Washington $331,929 $68,210 $14,838 $35,216 $15,728 $6,670 $20,832 Weld* $11,672,972 $3,679,816 $1,274,332 $480,454 $321,114 $102,540 $289,708 Yuma $586,636 $248,887 $41,692 $79,494 $32,472 $15,169 $20,847 Source: HAZUS 2007 & 2009 *Broomfield represents 2007 data; For 2010 update Adams, Boulder, Jefferson, and Weld Counties totals include Broomfield To develop the tables above, CDEM used building and content value data from the geodatabases supplied with the HAZUS software. The source files used were hzexposureoccupb, representing replacement cost values for the general building stock at the census block level, and hzexposurecontentb, representing content values for the general building stock at the census block level. Data was aggregated by county and occupancy class for the entire state. Total fields were added for seven of the basic occupancy classes (Residential, Commercial, Industrial, Colorado Natural Hazards Mitigation Plan 3 183

184 Agriculture, Religion, Government and Education) as well as per-capita totals fields. Fields were added to total all classes into one total for each county as well as a total per capita field for each county. Future Development The expansion of human development is in innate conflict the natural environment and its exposure to natural hazards. As population and commerce continue to spread across the state, the more potential and exposure our build environment has for impacts from natural events. Past and forecasted social and economic factors and trends are indicators of where and to what degree future development is going to come into contact with natural hazards. In addition to a discussion provided in the population overview from Section 2, Appendix C provides socioeconomic profiles that represent 14 distinct regions, Colorado State Demography Office in the Colorado Department of Local Affairs and last updated in Figure 3-56 depicts the statewide location of these regions. These profiles may be used for determining statewide future growth potential as well as that of smaller regions in relation to the geographic extent of natural hazards. The profiles provide highlights, estimates, and forecasts for the economy and job growth, income, and population and households. Included in each profile is a summary of anticipated population growth based primarily on economic factors. Further analysis and incorporation of these profiles will become more complete and continue in future planning processes. Figure 3 56: Colorado Planning and Management Regions Used for Socio Economic Profiles Colorado Natural Hazards Mitigation Plan 3 184

185 Potential Losses Requirement 201.4(c)(2)(iii): [The State risk assessment shall include an] overview and analysis of potential losses to the identified vulnerable structures, based on estimates provided in local risk assessments as well as the State risk assessment. The State shall estimate the potential dollar losses to State owned or operated buildings, infrastructure, and critical facilities located in the identified hazard areas. Requirement 201.4(d): Plan must be reviewed and revised to reflect changes in development Information presented and analysis conducted in previous portions of this State Plan update lends toward the estimation of potential losses. For loss estimation, information related to hazard identification, hazard profiles, and determination of vulnerability are rolled up to estimate losses in terms of the expected losses from hazard events to people, buildings, and other important assets. Primary areas of consideration within the loss estimation analysis for this State Plan update are listed below. State Asset Exposure Local Jurisdictions Future Development Estimation of potential losses in Colorado is cumulatively attributable to information presented throughout the State Plan, such as: Population characteristics as discussed in the Colorado Overview and Counties and Communities section. Regional socioeconomic profiles as presented in Appendix C. Information presented related to vulnerable county-level building and content value. State asset total value exposed by hazard. Estimates of potential losses for earthquake and flood were derived using FEMA s HAZUS loss estimation software. State Asset Losses Two primary considerations were used to evaluate and present potential losses to state facilities: one is real property losses, and the other, location and value of assets relative to the geographic extent of hazards. Real Property Losses With 7,573 state assets evaluated in the 2010 State Plan, it is expected that natural hazards occurring in Colorado impact state assets. Table 3-60 shows the number of real property losses by type of hazard. Between 2000 and 2010, the number of events resulting in reported real property losses to state facilities totaled 352. Wind and lightning Colorado Natural Hazards Mitigation Plan 3 185

186 damage accounted for 197, or 56 percent, of all reported events. Other property losses to state assets by natural hazards include: Extremely cold temperatures resulting in water pipes freezing, breaking, with resulting water or electrical damage. Hail damage to roofs and other exterior surfaces. Heavy, wet snowfalls causing roof or structural collapse. Heavy precipitation penetrating roof leaks or other structural openings with resulting water damage. Localized flooding resulting in water damage. Land movement (rock falls and mudslides) causing structural damage. Forest or grass fires burning structures or causing secondary effects from loss of power. Earthquake causing structural and pipe damage. Table 3 60: Number of Real Property Losses on State Assets by Hazard, 1/1/00 to 4/20/10 Natural Hazard Number of Loss Events Earthquake 2 Fire 5 Floods 11 Freezing (Winter Weather) 31 Hailstorms 37 Summer: Extreme Heat 1 Lightning 99 Precipitation 22 Landslide, Mudslide/Debris Flow, and Rockfalls 12 Winter Weather 34 Windstorms 98 Source: Office of Risk Management For future plan updates, details on the physical cost and other potential impacts of real property losses will be further considered. State Asset Potential Loss by Hazard Where feasible and/or existing data allowed, the list of Colorado State insured physical assets from the Office of Risk Management were analyzed against natural hazards to determine potential losses. Potential losses are equated to the total value of state assets exposed to any given hazard. The results of these analyses are shown in the tables below. The first table shows potential losses for where data was available to readily perform a loss analysis. Natural hazards with actual potential dollar losses shown include avalanche, expansive soils, fire, floods, landslides, hailstorms, subsidence, tornadoes, and Colorado Natural Hazards Mitigation Plan 3 186

187 windstorms. The second table indicates hazards for which loss estimates were not provided and provides further explanation on data limitations. Detailed analysis of potential state losses by hazard comprises Appendix B. This appendix provides potential vulnerability and loss of state assets by county where possible. In addition, potential losses by hazard are broken out by asset occupancy where data allows. Table 5-61 shows the analysis of expansive soils results in a state asset value potential loss of $17.5 billion, or about 97 percent of total statewide value. This high potential loss is due to the pervasive statewide geographic extent of expansive soils. Exposure of hailstorms, tornadoes, and windstorm to state assets also result in a high statewide potential loss of between $7.1 and $9.8 billion. Table 3 61: Potential Loss to State Assets by Hazard Natural Hazard Asset Total Asset Value Notes Avalanche 7 $70,456 Expansive Soils 6,511 $17,530,371,127 Fire 2,456 $1,470,787,308 Floods 802 $1,161,961,571 Landslide Potentially Unstable Soils Alluvial Fan / Debris Flow Rockfall $28,189 $18,915 $487,397 $2,254,705 Hailstorms 3,134 $8,718,300,908 Subsidence Potentially Collapsible Soil Undermined Land $294,272,000 $3,833,019,740 $294,271,704 Tornadoes 2,870 $7,122,526,135 Windstorms 3,450 $9,820,466,934 Expect enhanced avalanche geodata for next planning cycle. Heaving and expansive soil potential of greater than or equal to 3 percent. Includes assets in high and moderate wildfire areas. See flood plan for additional information. Specific geologic attributes used overlap, therefore listed independently. Counties with 250 or more reported hail events since Hazard layers overlap, therefore listed independently. Analyzed from counties with 20 or more tornadoes reported since Counties with 100 or more wind events reported since Hazards impacting, but without specific potential value losses associated with state assets are provided in Table Colorado Natural Hazards Mitigation Plan 3 187

188 Table 3 62: Hazards without Reported State Asset Potential Loss Natural Hazard Drought Earthquake Erosion and Deposition Extreme Heat Grasshopper Lightning Precipitation Thunderstorms Winter Weather Notes Direct impacts of drought on physical state assets are difficult to assess but likely losses are expected to be negligible. Analysis related to drought impacts on state forest and park lands, state land board property, state wildlife areas, and other property is included in the Colorado Drought Mitigation and Response Plan. Significant losses occur to buildings and infrastructure in HAZUS scenario results. State asset values lost per HAZUS run are not identified but potential losses are expected to be high depending on geographic location. Information to determine reliable loss estimates to state assets from erosion and deposition is unavailable. This hazard is often a result of human interaction with the physical environment that may have some impact various types of infrastructure or state lands. No existing workable data is available to determine reliable loss estimates on state assets as a result of extreme heat. There was one real property attributed to extreme heat, but it was directly related to a secondary power outage and overheating of electrical equipment. No known losses will occur to state assets related to grasshopper infestation. In the future, this analysis may be generalized to insect infestation with bark beetle as the primary focus. On an annual basis, an average of 10 real property losses occurs to state assets through lightning strikes. Future efforts will include working with the Office of Risk Management to better understand the circumstances and losses behind these reported events. There is not an existing reliable data layer to determine reliable loss estimates. A total of 22 real property losses were reported to state assets between 2000 and 2010, where impacts resulted from leaking roofs or related flooding. There is general geospatial information that suggests thunderstorms occur most frequently along the Front Range coinciding with the location of the majority of state asset value. However, there is not a meaningful data layer to determine reliable loss estimates related to this hazard. Specific losses are identified from some thunderstorm related hazards. No existing workable data to determine comprehensive loss estimates, however there were 65 real property losses related to freezing weather and collapsed roofs due to snow weight. Future efforts will include working with the Office of Risk Management to better understand the circumstances and losses behind these reported events. Colorado Natural Hazards Mitigation Plan 3 188

189 Local Jurisdictions The FEMA local hazard mitigation planning crosswalk dictates that inclusion of loss estimates is a should rather than a shall. The lack of a requirement for local plans to include loss estimates may suggest why in review of 28 local mitigation plans, approaches to vulnerability analysis often did not included a hazard-specific loss estimation component. Where possible, the State Plan hazard profiles included a county-level analysis of events and losses relative to the number of previous occurrences, number of deaths and injuries, and the amount of damage to properties and crops in dollars. This analysis was completed in order to augment risk as presented in jurisdictional plans and summarized in the Counties and Communities section of this plan. Although a generalized top-down approach of loss estimation may omit localized events not reported elsewhere, it nonetheless provides the best jurisdictional based analysis and lays the groundwork for future planning efforts. Local loss estimation presented in this section is based on local vulnerability assessments, and more particularly associated with the most highly ranked hazards from the local mitigation plans. These hazards include fire, flood, winter storm, and drought. Fire Wildland fire loss estimates would be expected to include short-term loss of life and loss of the value of destroyed or damaged homes, businesses, and infrastructure. However, losses associated with timber harvest value, decreased tourism, loss of wildlife habitat, degradation of water quality, loss of taxable assets to local government, and others are potential significant long-term losses that are difficult to quantitatively estimate. Identification of the number of local or countywide structures in rural or wildland/urban interface areas is challenging at the state level due to the intense data requirements of a statewide inventory of such structure locations. Statewide, there are about 160 Community Wildfire Protection Plans (CWPP) completed. Some of these plans are refined to provide a parcel by parcel risk assessment while others may identify risk at the subdivision level. Future analysis may involve looking at these 160 plans and rolling information that may contribute to loss estimation. CDEM staff engaged in discussion on how to present a summary of local loss estimation for fire outside of the 160 CWPPs but concluded that given available data, there was not an available sound or defendable methodology. Data is available for the amount of high risk land for wildfire by county as is the total valuation of building and content value by county. Evaluation of the relationship between frequency of occurrence, amount of high risk land, and countywide property value, data of which is all readily available, would result in loss estimates that are tenuous at best. Colorado Natural Hazards Mitigation Plan 3 189

190 Flood Estimates of potential vulnerability and losses associated with flood hazards are provided for in more detail in the Flood Hazard Mitigation Plan for Colorado. These estimates reflect both the population and structures within the 100-year floodplain. In addition to the review of loss estimates from local mitigation plans, HAZUS-MH flood model results provide the foundation for loss estimation for flooding for local jurisdictions. The HAZUS-MH flood model results included analysis for each of the 64 counties modeling streams draining a 10 square mile minimum drainage area, using 30 meter (1 arc second) Digital Elevation Models (DEM). Generated damage estimates are directly related to depth of flooding and are based on FEMA s depth-damage functions. For example, a two-foot flood generally results in about 20% damage to the structure (which translates to 20% of the structure s replacement value). The HAZUS-MH flood analysis results provide number of buildings impacted, estimates of the building repair costs, and the associated loss of building contents and business inventory. Building damage can cause additional losses to a community as a whole by restricting the building s ability to function properly. Income loss data accounts for losses such as business interruption and rental income losses as well as the resources associated with damage repair and job and housing losses. The jurisdictions most threatened and most vulnerable to damage or loss are presented in Figures 9 through 12 and Table 8 of the Flood Hazard Mitigation Plan for Colorado. IN addition, Appendix B of the State Plan includes a map showing total building loss by county based on HAZUS along with the supporting table. Based on the analysis of the HAZUS-MH level 1 flood loss modeling results the following conclusions were reached: Vulnerability to total direct economic building loss was determined to be highest in Denver, Arapahoe, Boulder, Larimer, Adams, El Paso, Pueblo, Jefferson, Weld, and Eagle Counties. Percent building damage would be highest in Prowers, Phillips, Morgan, Crowley, Eagle, Moffat, Clear Creek, Cheyenne, and Mineral. Arapahoe, Adams, Boulder, Denver, Weld, Larimer, El Paso, Jefferson, and Prowers face the highest risk of displaced population. These counties contain the major population centers in the state, thus, the potential displaced population is higher in these areas. The counties with the highest per capita loss include Prowers, Phillips, Mineral, Eagle, Hinsdale, Summit, Clear Creek, Pitkin, Morgan, and Moffat. Winter Storm Local loss estimation for winter storms focused on two measurements: death and injuries and building property damage. Colorado Natural Hazards Mitigation Plan 3 190

191 Death and injuries per year and the occurrence interval for one death or injury were derived to determine loss potential by county. Considering the number of snow and ice related automobile accidents statewide each season, the SHELDUS data used in this analysis is likely reporting significantly fewer injuries than actually occurred. Based on the analysis, counties along the Front Range indicated a propensity for shorter intervals for death and injury than the rest of the state. In particular, estimates for Denver, Boulder, El Paso, and Jefferson Counties all show a death or injury occurring every 2-5 years from winter storms. These counties also represent the most populated in Colorado. In contrast, counties showing the greatest occurrence interval such as Yuma, Phillips, Logan, Jackson, and Costilla represent some of the state s least populated areas. An analysis of estimated annual property damage from winter storms yielded similar results to the death and injury analysis. Boulder, Larimer, Jefferson, Douglas Counties, all along the Front Range, show an annual estimated property damage of greater than $180,000. Counties showing the least annual property damage estimates tended to be located along Colorado s Western Slope. In particular Moffat, Mesa, Garfield, Delta, and Montrose Counties all had less than $16,750 in estimated annual damage. In future planning efforts, the methodology to determine loss estimates will serve as a base as further analysis is preformed on hazards ranked as being a medium risk by local jurisdictions. Drought Annex B of the Colorado Drought Mitigation and Response Plan provides results of a detailed vulnerability assessment. Findings from the Drought Plan suggest that evaluation of the drought sections of existing local hazard mitigation plans found a lack of data available on economic losses. A recommendation is to begin recording economic losses due to drought on a county level. This can help to highlight areas and/or economic sectors that are particularly hard-hit, and can help counties anticipate the magnitude of losses that could potentially occur in future droughts. Drought losses are expected to intensify with population growth and development unless mitigation strategies are adopted. Counties with the highest estimated growth rates from (according to state demographer estimates) include Archuleta, Garfield, La Plata, Rio Blanco, Custer, Park, Elbert, and Weld. The impacts listed in Table 17, above, could become more severe in communities with a high rate of development and growth. Table 3-63 presents the impacts and estimated losses as taken from local mitigation plans. Colorado Natural Hazards Mitigation Plan 3 191

192 Table 3 63: Impacts and Estimated Losses from Local Hazard Mitigation Plans Local Risk Assessment Boulder County Costilla County Delta County DRCOG Dolores County El Paso County Elbert County Gunnison County Mesa County Northeast Colorado Region Northern Colorado Region Reported or Anticipated Impacts Impacts of future drought will vary by region. Agricultural industry expected to experience crop losses and livestock feeding expenses and deaths. The County will see an increase in dry fuels, beetle kill, associated wildfires, and loss of tourism revenue. Water supply issues for municipal, industrial, and domestic needs will be a concern for the entire county vulnerability increases with consecutive winters of below average snow pack. Agricultural impacts are one of the more significant economic effects to communities. Decrease in water availability can impact water quality and increase salinity, bacteria, turbidity, and temperature. Aquatic habitat can be impacted as a result. Using exposure analysis of the wildfire red zone, the total value of structures at risk (located in the red zone) in Costilla County is estimated at $96.4 million. The most significant impacts are to water intensive activities such as agriculture, wildfire protection, municipal usage, commerce, and tourism and recreation. Water quality deterioration can also occur. Data from Delta Area Development, Inc. indicates a total value of harvested cropland is $116.4 million. A future drought that causes a 20% loss of the total value in the county would result in potential losses of $23.3 million. Drought vulnerability not profiled. Drought was profiled but no vulnerability analysis was conducted. Agricultural Sector is usually the first to be impacted because of heavy dependence on stored soil water. Those who rely on surface water (i.e., reservoirs and lakes) and groundwater are usually the last to be affected. The most significant impacts from drought are related to water intensive activities, such as agriculture (i.e., crops and livestock), wildfire protection, municipal usage, commerce, recreation, and wildlife preservation; as well as a reduction of electric power generation and water quality deterioration. Secondary impacts of drought are wildfires, wind erosion, and soil compaction that can make an area more susceptible to flooding. Reduction in vegetation cover exposes soil to wind erosion. Quality of rivers and lake water can change and sediment transport regimes of streams can be altered, resulting in deteriorated water quality. Drought can impact agriculture and related businesses, which comprise a significant portion of the economy in Mesa County. The entire region is vulnerable to drought. With the majority land area of the region used for agricultural purposes, the planning area has significant exposure to this hazard. Available crop insurance data indicates over $644 million has been paid to the region s agricultural landowners in insurance claims between 1980 and It is reasonable to assume that a significant amount of this is due to droughtrelated losses. All residents, commercial facilities, industry, and agricultural businesses are impacted by this hazard. Specific buildings are not identified as being at risk since drought impacts the entire community. Colorado Natural Hazards Mitigation Plan 3 192

193 Local Risk Assessment Ouray County Park County Prowers County San Miguel County Summit County Teller County Upper Arkansas Area Reported or Anticipated Impacts The agricultural economy of the northern county will experience hardships, including agricultural losses, associated with a reduction in water supply. The southern county will see an increase in dry fuels, beetle kill, and associated wildfires and some loss of tourism revenue during the ski season. Water supply issues for domestic needs will be a concern for the entire county during droughts. One of the most significant economic effects is the impact on agriculture. Environmental drought impacts include both human and animal habitats and hydrologic units. Potential for a variety of secondary impacts, such as impacts to local commerce including tourism and providers of goods and services to Park County s agricultural community. Since the economy of Prowers County is so closely tied to agriculture and related businesses, the potential economic impact is severe. Water supply is affected both by decreased storage in reservoirs and dry wells resulting from a lowering of the water table. Impacts of future drought will vary depending on the region. The agricultural economy of the west end will experience hardships associated with a reduction in water supply. The eastern end will see an increase in dry fuels, beetle kill, associated wildfires, and loss of tourism revenue during the ski season. Hydroelectric power plants within the county may have reduced power generation during drought. Ongoing drought has left areas more prone to beetle kill and associated wildfires. Other past impacts of drought include degradation of air quality due to dust, reduction of tourism and recreation activities, and damage to the ranching economy in the Lower Blue Basin. Impacts to agriculture including losses and livestock feeding expenses and deaths. Increase in dry fuels, beetle kill, associated wildfires, and some loss of tourism revenue. Water supply issues for domestic needs will be a concern for the entire county during droughts. The vulnerability of community assets to drought is tending to increase through time as the demand for limited raw water resources goes up. Economic assets such as the rafting and skiing industries prosper and suffer as precipitation fluctuates and competition for water from the Front Range increases. Earthquake In addition to including loss estimates on the top four high risk hazards as identified in local mitigation plans, results of a HAZUS earthquake analysis performed in 2004 are presented as still valid for this State Plan update. Colorado s earthquake hazard and risk has historically been rated lower than most knowledgeable scientists in the state consider justified. As a result, local emergency managers are generally unaware of the size and consequences of an earthquake that could occur in the state. HAZUS 99 gave a probabilistic Annualized Earthquake Loss (AEL) of $5.8 million which ranked Colorado 30 th in the nation. Colorado Natural Hazards Mitigation Plan 3 193

194 The Colorado Geological Survey (CGS) recently ran a series of deterministic scenarios for selected faults around the state using HAZUS MH. The earthquake magnitudes used for each fault were the Maximum Credible Earthquake taken from the USGS Quaternary Fault and Fold Database or from the USGS National Earthquake Hazard Map. The results demonstrate that the probabilistic AEL value of $5.8 million does not begin to convey the size of the loss that would occur in the event of a strong earthquake on any of these faults. For example, a magnitude 6.5 earthquake on the Golden fault is forecast to result in a $22 billion economic loss. Or, consider that a magnitude 6.0 earthquake under the Rocky Mountain Arsenal would result in $3.9 billion economic loss to Adams County alone; and a loss ratio of 17% that would make recovery difficult. The following lists represent a summary of loss estimation by county and fault. Detailed loss estimates by county and fault are presented in Appendix B Most Damaging Faults 1. Rocky Mountain Arsenal 2. Golden 3. Rampart Range 4. Ute Pass 5. Walnut Creek Total Direct Economic Loss by Fault 1. Rocky Mountain Arsenal, M6.5, Counties 150km, CEUS $24.83 Billion 2. Golden, M6.5, Counties 150km, CEUS - $22.08 Billion 3. Rampart Range, M7, Counties 150km, CEUS - $18.26 Billion 4. Walnut Creek, M6, Counties 150km, CEUS - $13.25 Billion 5. Ute Pass, M7, Counties 150km, CEUS $12.88 Billion 6. Rocky Mountain Arsenal, M6, Counties 150km, CEUS - $12.13 Billion 7. Golden, M6, Counties, 150km, CEUS - $11.41 Billion 8. Rampart Range, M7, Counties 150km, WUS - $11.25 Billion 9. Ute Pass, M7, Counties 150km, WUS - $9.77 Billion 10. Ute Pass, M7 Reverse, El Paso County, WUS $9.30 Billion 11. Rampart Range, M7, El Paso County, WUS - $8.15 Billion 12. Golden, M6.5, Jefferson County, CEUS - $8.14 Billion 13. Ute Pass, M7, El Paso County, WUS - $7.92 Billion 14. Rampart, M6.5, Counties 150km, CEUS - $7.04 Billion Highest Loss Ratio 1. Rocky Mountain Arsenal, M6.5, Adams County, CEUS 29.7% 2. Ute Pass, M7 Reverse, El Paso County, WUS 26.8 % 3. South Sawatch, M7.25, Chaffee County, WUS 24.1% Colorado Natural Hazards Mitigation Plan 3 194

195 4. Rampart, M7, El Paso County, WUS 23.5% 5. Ute Pass, M7, El Paso County, WUS 22.9% Counties at Greatest Risk (high monetary loss, casualties, and loss ratios) 1. El Paso County 2. Jefferson County 3. Denver County 4. Summit County 5. Chaffee County Future Development Population growth in a few Front Range counties and mountains over the last 20 years has generally outpaced the rest of the state. For several years in the 1990s and into the 2000s, Douglas County, located on the southern edge of the Denver region, was the fastest growing county in the United States relative to percent population change. Elbert County, adjacent to and directly east of Douglas County has also experienced high rate of population growth. Any population growth on the Front Range puts more people at risk of death or injury to inclement atmospheric hazards such as thunderstorms and related hazards such as lightning, tornadoes, hailstorms, and windstorms. In the central mountains, Park, Lake, and Eagle Counties have experienced high rates of annual average population growth over the last 20 years. Population growth in mountainous areas increases population to the risk of geologic hazards such as avalanche, landslide, and rockfalls, in addition to more frequent severe winter weather than the rest of the state. In addition to increased risk of hazards to the people in growth areas, the associated buildings and infrastructure to support such population growth is also put into harms way. In future plan updates, local building and content values will be evaluated relative to changes in number and value over time. The resulting quantitative change serves as an indicator of growth that can be measured against future probability of the hazard occurring to better determine risk to future development. Appendix C provides socioeconomic profiles for 14 regions of Colorado, covering all of the State s 64 counties. Each profile provides a discussion related to where, when and why future residential and commercial growth will occur across the state. Colorado Natural Hazards Mitigation Plan 3 195

196 Consequence Analysis The Emergency Management Accreditation Program (EMAP) standard for a risk assessment requires the state program to include a consequence analysis for hazards identified in the State Plan. The consequence analysis in this State Plan update considers the impact to the following: General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity Of Government And Services Confidence in Government Critical Assets The analysis of consequence by hazard for this State Plan update was accomplished through a two step process. The first step consisted of a SHMT workshop; the second step consisted of CDEM staff contributions upon completion of hazard profiles and the determination of vulnerability and potential losses. The SHMT gathered for a discussion-based workshop to determine consequences for selected hazards (flood, thunderstorms, fire, winter weather, and earthquake). Because the workshop was a first iteration of this type of analysis for the SHMT, expertise in attendance and the desire to evaluate a broad range of events drove the focus on these hazards. Because not all hazards were covered in the workshop, and because additional analysis was performed as part of the risk assessment, CDEM staff augmented the original consequence analysis with findings for all remaining identified hazards and provided updates to ones previously completed. Identified consequences and associated descriptions by hazard are provided in the tables below. Colorado Natural Hazards Mitigation Plan 3 196

197 Avalanche Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description There are 6 to 7 annual deaths along with multiple injuries with most deaths and injuries mostly impacting winter sport and backcountry recreationists such as skiers and snowboarders, hikers, and snowmobilers. Highway maintenance crews and motorists are also at risk of avalanche near or on roadways. Some exposure exists to personnel performing routine duties on roadways and other areas that may be prone to events. Some responders may face risk of avalanches during response if entering avalanche prone areas, however most avalanche related duties are post event where risk of occurrence has subsided. Instances of personal property losses are infrequent yet occur on occasion. Known avalanche runs are typically void of development due to local land use regulations. Some events will impact private vehicles. Buildings and equipment are typically not located within avalanche runs due to their known locations and local land use regulations. Roadways are blocked by avalanches but typically do not sustain significant damage. Communication and power infrastructure occasionally experiences shortterm or minor impacts. Possible short term blockage of roadways that prevent travel and access to local businesses by residents, recreationists, and tourists. Due to limited exposure of property to this hazard, economic losses resulting from damage to buildings and personal property or associated downtime are anticipated to be limited. Localized impact related to tree damage may be found in or around shoots. Removal or displacement of trees and rocks may cause secondary impacts such as landslides or rockfalls as slope stability is impacted. There is potential for the short term damming and sudden release of water if event intersects a waterway. Loss of facilities or infrastructure for the provision of government services is expected to be non existent or negligible. Possible short term accessibility issues for first responders performing routine duties or personnel reporting to work locations. Characteristics of avalanches result in limited response and recovery functions for government beyond first responders. Monitoring programs typically mitigate potential large scale events and road crews are typically swift in restoring service to blocked roadways. Risk to any critical assets is limited due to few state or local facilities located within avalanche runs. Colorado Natural Hazards Mitigation Plan 3 197

198 Drought Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Water supply disruptions and reduced water quality could impact service delivery. Air quality from blowing dust could have detrimental heath impacts. Mental health issues such as stress, anxiety, depression, and addiction recurrence may arise with loss of income in agricultural areas. Minor impacts are anticipated to properly equipped and trained personnel, though dust storms may require special equipment. Nature of hazard expected to have minimal impact on buildings and other personal property. Damaged landscaping from municipal water restrictions or priority water rights restrictions may occur. Increased secondary risk of wildfire may threaten property. Infrastructure can be damaged by excessively dry expansive soil as it contracts. Dams and ditches can experience structural damage due to decreased pore water pressure, damage caused by high sediment loads when pulling water from the bottom of reservoirs, and damage caused by debris flows and flooding following wildfires. Local economy and finances dependent on consistent water supply or precipitation (i.e. snow at ski areas) may be adversely affected for duration of drought. Agricultural economies are adversely affected if drought results in widespread loss of crop or yield reductions. Additional information is provided in the sector analyses for Recreation and Tourism, Agriculture, State Assets, Energy, Municipal and Industrial, and Socioeconomic in the attached drought mitigation plan. May cause disruptions in wildlife habitat, resulting in an increasing interface with people, or reducing numbers of animals if forage becomes too sparse. Land quality can be negatively impacted by overgrazing during drought. Water quality can become degraded to the point of causing localized fish kills. Low stream flows will have negative impacts on riparian habitats and aquatic species. See Environment Sector analysis in attached drought mitigation annex for a detailed impact discussion. Slow onset and nature of drought makes it unlikely to have an impact on continuity of operations. Nature of hazard not expected to impact delivery of government services, except for moderate impact on water utilities. In extreme cases municipal water delivery may be interrupted. Ability to deliver recreational services may be impacted at the local level. Food supply and delivery could be disrupted, with an associated increase in food prices. Ability to respond and recover may be impaired if planning, response, and recovery not timely and effective. State Government must strike balance between over reaction and under response to the drought hazard. Risk to critical assets are not anticipated, however dust accumulation may result in limited impact on any sensitive equipment. Colorado Natural Hazards Mitigation Plan 3 198

199 Earthquake Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description In a significant event (6 7 magnitude), there is high expectation of a mass casualties and/or fatalities. Anyone caught in a vulnerable structure during an event is at risk. There is limited earthquake preparedness activity in Colorado. Exposure exists to personnel performing routine duties when event occurs, although event related duties are primarily post event. Unsafe structural or environmental conditions may persist during the response period putting search and rescue personnel and other responders at risk. Scale of event will likely overwhelm local resources and require mutual aid assistance from outside the area of impact. Buildings, vehicles, signage, and/or any unsecured property may be damaged or destroyed during a significant event. HAZUS loss estimation scenario results returned billions of dollars in loss related to faults capable of 6 7 magnitude quakes. Lesser magnitude events in the 5 range may cost millions in damage depending on impacted area. Buildings, equipment, and utility infrastructure are typically not constructed in Colorado to withstand a 6 7 magnitude quake. There is potential for high impact of destruction or usability. Communications would be negatively impacted. Potential loss of facilities or infrastructure function or accessibility and uninsured damages. HAZUS loss estimation scenario results for a 6.5 magnitude event on the Golden fault resulted in a loss of $22 billion. Lesser magnitude earthquakes in the Denver region have caused millions of dollars in damages. Difficult to assess environmental damage due to variability in location and magnitude. Possible cascading water quality issues from damaged water treatment facilities or impacts to ground and air quality from hazardous material leaks. Loss of facilities or infrastructure function or accessibility or ability to provide services. Power interruption is likely if not adequately equipped with backup generation. Large scale of event will typically overwhelm emergency response and coordination services and may require mutual aid assistance from outside the impacted area. Public holds high expectations of government capabilities for public information and response and recovery activities related to large scale disaster events such as earthquake. High expectations for rapid restoration of critical lifelines. Expected damage to water treatment facilities, government buildings, public safety facilities, power generation and distribution, and healthcare facilities. Colorado Natural Hazards Mitigation Plan 3 199

200 Erosion and Deposition Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Property owners, farmers, construction workers may be directly impacted by typically limited and localized events. Little if any exposure exists to personnel performing routine duties when event occurs. First responders will not directly report to erosion and deposition events, rather to cascading or unintended consequences resulting from it. Instances of property loss may occur if streamside property is undercut, construction activities induce an event, or buildings are placed in event prone geology. Physical loss of land may occur as erosion carries land from one property and deposits it on another. Severe erosion may remove the earth from beneath bridges, roads and foundations of structures adjacent to streams. None or limited loss of facilities or infrastructure function or accessibility and limited uninsured damages. This event innately impacts land and water. Earth materials are physically moved from one place to another and under certain circumstances, may be significant. Water quality may be impacted from siltation. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. Event characteristics such as duration and speed of onset result in limited response and recovery functions for government beyond first responders. If infrastructure damage occurs, such as a road washout, quick and cost effective repair is expected. Risk to critical assets is not anticipated; however scour may result in bridge closures. Colorado Natural Hazards Mitigation Plan 3 200

201 Expansive Soils Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Risk is related to anything built on the ground that may be affected from slow movement. Homeowners, developers, and owners of public facilities and infrastructure. CGS reports that one in five people is affected by expansive soils. Some exposure exists to personnel performing routine duties after a specific site is impacted and unstable. Instances of property losses due to shrinking and swelling can cause major or long term property damage impacting structural stability. Instances of infrastructure damage due to shrinking and swelling can cause major or long term structural damage. None or limited loss of facilities or infrastructure function or accessibility and limited uninsured damages. Limited impact anticipated to the environment other than changes in soil characteristics. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. May have limited power interruption if not adequately equipped with backup generation. Characteristics of expansive soils such as duration and speed of onset result in limited response functions for government beyond building inspection and repair. Risk to any critical asset that does not have adequate mitigation actions taken during construction. Colorado Natural Hazards Mitigation Plan 3 201

202 Fire Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Deaths and injury have occurred in past events. Staff, recreationists, campers, property owners in remote areas or the wildland urban interface areas, and persons with breathing difficulties may all be impacted. Secondary impacts may negatively affect water quality and downstream water users. Exposure exists to response personnel performing routine duties when event occurs; fire event related duties may cause significant danger to response personnel including evacuation, suppression, law enforcement, and damage assessment. The tragic event on Storm King Mountain near Glenwood Springs took the lives of 14 firefighters. Buildings, vehicles, signage, and/or any unsecured property may be affected during an event. Property may be destroyed, have significant structural damage, or be affected by smoke. State historical, recreational, natural and wildlife properties/facilities at risk. The Fourmile Canyon fire in Boulder County resulted in a preliminary insured loss estimate of over $200 million. Buildings, equipment, vehicles, and communications and utility infrastructure are exposed and lost to wildfires every year in Colorado. The number of state assets in high or moderate fire risk areas total 2,456. State asset value located in high or moderate fire risk areas is $1.5 billion. Potential loss of facilities or infrastructure function or accessibility and uninsured damages. Potential impact to tourism and land development activities depending on severity of the fire season and location of fire events. Depending on nature of area where fire occurs, many home based businesses will be impacted due to evacuation, lack of utility service, or through destruction of property. Significant impact related to loss of forest or grasslands, impacts to water quality, erosion and sedimentation may affect critical infrastructure and natural waterways. Loss of ground vegetation may encourage landslides, mudslides, or other geologic movement of land. Dead or damaged trees are at risk of falling. Annual average of 86 square miles of state and private land is burned. Potential loss of facilities or infrastructure function or accessibility or ability to provide services. Power interruption is likely if not adequately equipped with backup generation. Potential decrease in property tax collection by local government and special districts due to loss of structure or land value may impact service provision. Public holds high expectations of government capabilities for warning, public information, and response and recovery activities related to wildfires. Recent and past events indicated a high expectation from evacuees for the provision of real time property level damage assessments (e.g., what properties are confirmed destroyed, damaged, or unaffected). Potential impact to water treatment facilities, government buildings, public safety facilities and equipment, healthcare services. Scour on bridge pilings may result in bridge and road closures. Colorado Natural Hazards Mitigation Plan 3 202

203 Flood Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Impacts of people will change with characteristic of event (e.g., flash flood in a canyon, river flood on the plains, etc.). Localized impacts may be severe with moderate to light impacts for outward or other affected areas. The Big Thompson flood event which resulted from localized heavy rainfall and a subsequent flash flood took the lives of 145 people. Residents/property owners without flood insurance may be impacted greater than those with coverage. Residents may be displaced due to evacuation, damage, or inaccessibility to homes. Persons within flood areas have the potential for direct contact with hazardous materials. Need for evacuation support such as door to door notification and traffic management may increase responder risk as event escalates. Localized impact expected to limit damage to personnel in flood areas at the time of incident. Impacts to transportation corridors and communications lines may affect responder ability to effectively respond. There may be a higher risk to responders in flash flood events which are prevalent in the State. Private property losses with increased risk to those without flood insurance. Localized impact to facilities and infrastructure in incident area. Some severe damage possible. Critical facilities may be impacted by flooding: communications, hospitals, schools, nursing homes, utilities, wastewater TP/WTP, roadways. Local economy and finances adversely affected, possibly for an extended period of time depending on damage and length of investigation. Localized disruption of roads, facilities, and/or utilities caused by incident may postpone delivery of some services. Localized impact expected to be severe for incident areas and moderate to light for other areas affected by flood. Wetland impacts due to flooding can result in water quality impacts and wildlife habitat impacts. Orphan drums (containers that may contain hazardous materials). Commercial hazmat/hazardous waste. Household hazardous waste. Releases from transportation. Releases into streams and rivers; drinking water supply; ground water; air. Damage to facilities/personnel in incident area may require temporary relocation of some operations. Ability to respond and recover may be questioned and challenged if planning, response, and recovery not timely and effective. Critical facilities may be impacted by flooding such as those related to communications, hospitals, schools, nursing homes, utilities, wastewater treatment plants, and roadways. Colorado Natural Hazards Mitigation Plan 3 203

204 Grasshopper Infestation Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Persons in agriculture and livestock industry. Mental health issues such as stress, anxiety, depression, and addiction recurrence may arise with loss of income in agricultural areas. No impact. Property impacts are likely limited to vegetation loss with cascading effects of erosion and deposition. No impact. Crop and rangeland damage occur on an annual basis and in outbreak years, large amounts of rangeland and crops may be destroyed. Cost of damage to farmers and ranchers can reach into the millions of dollars in outbreak years. During a severe outbreak, grasshoppers may remove more vegetation that cattle in a given pasture and perpetuate erosion through the degradation of vegetation. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. Expectations of farmers and ranchers are largely related to the provision of financial resources for insecticides and the availability of financial assistance through disaster declarations. No impact. Colorado Natural Hazards Mitigation Plan 3 204

205 Hailstorms Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Injuries and deaths have occurred from hail. Motorists, outdoor workers, outdoor recreationists are at risk from direct impact or deteriorated road conditions due to precipitation on the road surface. Some exposure exists to personnel performing routine duties when event occurs; otherwise storm related duties are typically post event. Some impact related to unsafe road surface conditions from hail on roadways. Generally, many instances of small amounts of damage reflect high event wide property losses, including structures and vehicles. Buildings and equipment are exposed to hailstorms; however there is typically limited loss of facility use or infrastructure function or accessibility and limited uninsured damages. Value of state assets located in highest hail prone counties totals over 8.7 billion. Insurance claims from large hailstorms tend to be small in amount (i.e., property by property damages) but high in the total number of claims which results in high aggregate insured losses. Crop damage and loss to farmers may be significant and result in agricultural disaster declarations. Limited short term impacts such as leaf and small limb removal from leaves and plants. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. Characteristics of hailstorms such as duration and speed of onset result in limited response and recovery functions for government beyond first responders. Buildings and equipment are exposed to hailstorms but damage to such should not typically amount to disruption or debilitating damage to critical assets. Colorado Natural Hazards Mitigation Plan 3 205

206 Landslides, Mud and Debris Flow, and Rockfalls Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description At risk are people in areas burned by wildfires, motorists along highways, tourists and recreationists on or near steep slopes. Possible deaths, injuries, and property loss. Some exposure exists to personnel performing routine duties when event occurs; some post event duties may expose personnel to areas of geologic instability. Limited damage to personal property occurs from this event. Occasional vehicles are struck by falling rocks or debris. Postprecipitation events in burn areas have resulted in active debris flows causing significant damage. Transportation infrastructure is typically the most impacted resource in Colorado from landslides and rockfalls though residential structures have also been impacted. Alluvial fan and debris flows areas hold $2.2 billion in state asset value with limited impact. With a large enough event, closure of transportation routes may result negative impact on Colorado s tourism industry. Events may expose addition earth that is prone to the same movement, perpetuating the hazard. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. Duration of response and repair to closed or blocked roadways is a visible and often reported in the media which may lead to public perceptions of capability. Limited buildings and equipment are exposed to this hazard but damage to such should not typically amount to disruption or debilitating damage. Colorado Natural Hazards Mitigation Plan 3 206

207 Lightning Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Outdoor workers, outdoor recreationists, outdoor sporting participants; population of the counties determined most at risk. Some exposure exists to personnel performing routine duties when event occurs; otherwise storm related duties are typically post event. Instances of property losses due to trees or roof tops being struck. Direct flash strikes or near power surges may impact electronic equipment. Buildings and equipment are exposed to lightning as well as utility infrastructure. Assets in areas with higher flash counts are at greater risk. None or limited loss of facilities or infrastructure function or accessibility and limited uninsured damages. Limited impact related to tree damage. Lightning strike may be precursor to wildfire under certain conditions. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. May have limited power interruption if not adequately equipped with backup generation. Characteristics of lightning flashes such as duration and speed of onset result in limited response and recovery functions for government beyond first responders. Risk to any critical asset sector that is energy dependant without adequate backup generation. Colorado Natural Hazards Mitigation Plan 3 207

208 Precipitation Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Motorists, outdoor workers, outdoor recreationists, outdoor sporting participants; population of the counties determined most at risk. Some exposure exists to personnel performing routine duties when event occurs; storm related duties may be during event. Snow, heavy rain, hail may provide adverse conditions. Buildings and equipment are exposed to hailstorms. Heavy snow resulting in structural collapse. Buildings, equipment, and utility infrastructure are exposed to hailstorms and heavy snow and rain. Value of state assets located in highest hail prone counties totals over 8.7 billion. Majority of state losses attributable to precipitation related events. Potential loss of facilities or infrastructure function or accessibility and uninsured damages. Impact to transportation sector and movement of goods. Limited impact related to tree damage. Potential for high impact related to stream flow and overall water availability. May serve as precursor to other hazards such as flood, land movement, drought, and winter storm. Potential loss of facilities or infrastructure function or accessibility or ability to provide services. May have power interruption if not adequately equipped with backup generation. Regional limitations to mobility from heavy snowfall. Public holds high expectations of government capabilities for reducing impact of snow and ice events related to transportation (roads, bridges, airports, rail). High expectations for rapid power restoration. Potential impact on power infrastructure from heavy snow or ice accumulation. Risk may come from secondary hazards such as flooding, mudslides, rockfalls, etc. Colorado Natural Hazards Mitigation Plan 3 208

209 Subsidence Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Homeowners, developers, and owners of public and private facilities and infrastructure. Some exposure exists to personnel performing routine duties after a specific site is impacted and unstable. Subsidence can result in serious structural damage to buildings, roads, irrigation ditches, underground utilities and pipelines. Instances of infrastructure damage due to compressing soil can cause major or longterm structural damage. Subsidence can result in serious structural damage to buildings, roads, irrigation ditches, underground utilities and pipelines None or limited loss of facilities or infrastructure function or accessibility and limited uninsured damages. Limited impact related to tree damage. Lightning strikes are a leading cause of wildland fires which may result in significant damage to forests, grasslands, and water quality. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. May have limited power interruption if not adequately equipped with backup generation. Characteristics of expansive soils such as duration and speed of onset result in limited response functions for government beyond building inspection and repair. Risk to any critical asset that does not have adequate mitigation actions taken during construction. Colorado Natural Hazards Mitigation Plan 3 209

210 Summertime: Extreme Heat Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Motorists, outdoor workers, outdoor recreationists, persons without access to air conditioning, persons with pre existing medical conditions; people with emergency dependant medical treatment; population of the regions typical of higher temperatures. Exposure exists to personnel performing routine duties when event occurs; potential higher impact to responders wearing heavy equipment or uniforms or prone to physical exertion. Potential impact to temperature sensitive property such as food items or information technology if access to power supply is disrupted. Loss of power due to over usage of electricity supply related to cooling. Sagging electric transmission lines more apt to fail. Increased demand on water infrastructure. Potential risk to agricultural products if accompanied by prolonged drought. Typically accompanied by little precipitation and low humidity with increased fire risks and water supply. Loss of power due to over usage of electricity supply related to cooling. Characteristics of extreme heat events limited response and recovery functions for government beyond first responders. Provision of cooling centers may relate to public perception of emergency service. High stress on power grid due to energy usage related to cooling. Risk to any critical asset sector that is energy dependant without adequate backup generation. Colorado Natural Hazards Mitigation Plan 3 210

211 Thunderstorms Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Motorists, outdoor workers, outdoor recreationists, outdoor sporting participants; persons with power dependant medical conditions; population of the counties determined most at risk. Some exposure exists to personnel performing routine duties when event occurs; storm related duties may be during event. Wind, heavy rain, hail, tornadoes, and lightning may provide adverse conditions. Buildings and equipment are exposed to hail, tornadoes, lightning, and winds. Structural damage may range from destruction to minor depending on storm characteristics. Buildings, equipment, and utility infrastructure are exposed to wind, heavy rain, hail, tornadoes, and lightning. Majority of state asset value located along Front Range and eastern Colorado where most severe thunderstorm activity takes place. Minimal impact to facilities or infrastructure function or accessibility and uninsured damages. More severe thunderstorm characteristics such as tornado are expected to have greater impact. Limited impact related to tree damage, such as leaf and small limb fall from hail and wind. Greater environmental impacts will occur from specific wind events such as microburst or straight line winds or tornadoes. Potential loss of facilities or infrastructure function or accessibility or ability to provide services. May have power interruption if not adequately equipped with backup generation. Regional limitations to mobility from heavy snowfall. Public does not hold high expectations of government capabilities for reducing impact of general thunderstorms. Specific characteristics of any given storm such as tornadoes will result in varying expectations. High expectations for rapid power restoration. Buildings, equipment, and utility infrastructure are exposed to wind, heavy rain, hail, tornadoes, and lightning. Majority of state asset value located along Front Range and eastern Colorado where most severe thunderstorm activity takes place. Colorado Natural Hazards Mitigation Plan 3 211

212 Tornado Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Anyone without adequate shelter during an event; population of the counties determined most at risk. High risk of injury and death. Exposure exists to personnel performing routine duties when event occurs; storm related duties are primarily post event, however unsafe structural or environmental conditions may persist during the response period. Buildings, vehicles, signage, and/or any unsecured property may be affected during an event. Property may be destroyed or have significant damage. Buildings, equipment, and utility infrastructure are exposed to tornadoes and heavy snow and rain. Value of state assets located in highest hailprone counties totals over 8.7 billion. Majority of state losses attributable to precipitation related events. Potential loss of facilities or infrastructure function or accessibility and uninsured damages. Impact to transportation sector and movement of goods. Historic events in Colorado have impacted community business districts where a majority of businesses are lost. Significant impact related to tree damage. Possible cascading water quality issues from damaged water treatment facilities. Loss of facilities or infrastructure function or accessibility or ability to provide services. Power interruption is likely if not adequately equipped with backup generation. Public holds high expectations of government capabilities for warning, public information, and response and recovery activities related to a tornado. High expectations for rapid restoration of critical lifelines. Potential impact to water treatment facilities, government buildings, public safety facilities and equipment, healthcare services. Colorado Natural Hazards Mitigation Plan 3 212

213 Windstorms Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Motorists, air travelers, outdoor workers, outdoor recreationists; population of the counties determined most at risk. Some exposure exists to personnel performing routine duties when event occurs; otherwise storm related duties are typically post event. Some instances of small amounts of property damage to structures and vehicles. Falling limbs or trees may impact property. Buildings and equipment are exposed to windstorms. Value of state assets located in highest wind prone counties is high. None or limited loss of facilities or infrastructure function or accessibility and limited uninsured damages. Typically leaf and small limb removal from trees and plants; some microburst or straight line winds will down large limbs or trees. Limited short term impacts. None or limited loss of facilities or infrastructure function or accessibility or ability to provide services. Characteristics of windstorms such as duration and speed of onset result in limited response and recovery functions for government beyond first responders. Potential exposure and short term impact to buildings and utility and communications infrastructure. Colorado Natural Hazards Mitigation Plan 3 213

214 Winter Weather Consideration General Public First Responders Property Facilities and Infrastructure Economic Environment Continuity of Government and Services Confidence in Government Critical Assets Description Motorists, outdoor workers, outdoor recreationists, outdoor sporting participants; homeless persons; persons with energy dependant medical needs; persons with pre existing medical conditions; statewide population. Exposure exists to personnel performing routine duties when event occurs; stormrelated duties may be during event. Snow and blowing snow, ice, and extreme cold will provide adverse working conditions. Buildings, vehicles, and equipment are exposed to winter weather. Heavy snow and ice, complicated by strong winds, may result in structural damage, collapse, or instability. Buildings, equipment, and utility infrastructure are exposed to heavy snow and ice, sometimes complicated by strong winds. Majority of state losses attributable to precipitation related events, many winter related. Limited access to or ability to maintain operations of public transportation or access to transportation hubs. Potential loss of facilities or infrastructure function or accessibility and uninsured damages. Impact to transportation sector and movement of goods. Lost revenue to decreased business patronage or inability of workers to reach employment locations. Impact related to tree damage, particularly ice and snow buildup resulting in downed limbs. May serve as precursor to other hazards such as avalanche. Potential loss of facilities or infrastructure function or accessibility or ability to provide services. May have power interruption if not adequately equipped with backup generation. Regional limitations to mobility from heavy snowfall affecting workforce/essential personnel. Public holds high expectations of government capabilities for reducing impact of snow and ice events related to transportation (roads, bridges, airports, rail). High expectations for rapid power restoration. Buildings, equipment, and utility infrastructure are exposed to heavy snow and ice, sometimes complicated by strong winds. Majority of state losses attributable to precipitation related events, many winter related. Limited access to or ability to maintain operations of public transportation or access to transportation hubs. Colorado Natural Hazards Mitigation Plan 3 214