Center for Western Weather and Water Extremes An Introduction and the Topic of Drought

Transcription

1 Center for Western Weather and Water Extremes An Introduction and the Topic of Drought Dr. F. Martin Ralph UCSD/Scripps Institution of Oceanography La Jolla, CA Drought Response Workshop Irvine, California, 8 October 2013

2 Outline A brief introduction to CW3E Atmospheric Rivers (AR) ARs as Drought Busters Mike Dettinger The Analog Years concept Anne Steinemann

3 Atmospheric Rivers (fall and winter) Great Plains Deep Convection (spring and summer) Spring Front Range Upslope (rain/snow) Southwest Monsoon (summer & fall) Center for Western Weather and Water Extremes Where: Scripps Institution of Oceanography UCSD/Scripps Inst. Oceanography La Jolla, California When: Start Who: Dr. F. M. Ralph (Director) Dr. Dan Cayan Dr. Mike Dettinger Mission Provide 21 st Century water cycle science, technology and outreach to support effective policies and practices that address the impacts of extreme weather and water events on the environment, people and the economy of Western North America Goal Revolutionize the physical understanding, observations, weather predictions and climate projections of extreme events in Western North America, including atmospheric rivers and the North American summer monsoon as well as their impacts on floods, droughts, hydropower, ecosystems and the economy

4 Major Activities Create a Hydroclimate Testbed (HCT) jointly with NOAA o Represents a climate-focused analog to NOAA s Hydrometeorology Testbed (HMT) o Informed by lessons from NOAA/HMT, RISAs (CNAP, CLIMAS, WWA, CIRC), NIDIS, DOI Climate Science Centers, USGS ARkStorm Advance scientific understanding of atmospheric rivers and their role in extreme events o Quantify contributions to flooding and characteristics that distinguish events that produce floods from those that do not o Evaluate the role in modulating water supply and drought Use and develop state-of-the-art observing systems to study the roles of atmospheric rivers, orographic precipitation, boundary layer, soil moisture and microphysical process in water cycle extreme events o Utilize the HMT-West Legacy Network sponsored by DWR/EFREP o Evaluate and recommend observing network alternatives for the Western U.S. for extreme events Develop prototype techniques to improve extreme event predictions and projections - from short-term (days) to medium range (weeks) and beyond (e.g., seasonal) o Decision support tools for resource managers dealing with issues from hours to seasons to decades

5 NOAA s HMT Focus on extreme precipitation NOAA s Hydrometeorology Testbed (HMT) Connects researchers, forecasters and forecast users Has been researching and developing prototypes on extreme precipitation in California since 2003 Testing and applying results to the Pacific Northwest Builds on earlier experiments from Lessons learned from HMT have been documented in over 50 formal peer-reviewed technical publications

6 Flooding on California s Russian River: Role of atmospheric rivers Ralph, F.M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger, D. R. Cayan, A. White Geophys. Res. Lett., 2006 Russian River floods are associated with atmospheric rivers - all 7 floods over 8 years. SSM/I satellite data shows atmospheric river Stream gauge data show regional extent of high stream flow covers 500 km of coast Flooding in Western Washington: The Connection to Atmospheric Rivers Paul J. Neiman, Lawrence J. Schick, F. Martin Ralph, Mimi Hughes, and Gary A. Wick J. Hydrometeorology (2011) Of 48 annual peak daily flows on 4 watersheds, 46 were associated with the land-fall of atmospheric river conditions. 6

7 Article in Scientific American Describes atmospheric rivers as key to west coast mega floods (Dettinger and Ingram January 2013)

8 Atmospheric River Events 20 Nov-3 Dec 2012 Animation courtesy of Don Murray (NOAA/ESRL/PSD)

9 Atmospheric Rivers, Floods and the Water Resources of California by Mike Dettinger, Marty Ralph,, Tapash Das, Paul Neiman, Dan Cayan Water, 2011 (in Press) 25-35% of annual precipitation in the Pacific Northwest fell in association with atmospheric river events An average AR transports the equivalent of 7.5 times the average discharge of the Mississippi River, or ~10 M acre feet/day 35-45% of annual precipitation in California fell in association with atmospheric river events

10 Northern Sierra 8-station index as of 18 March 2012 Increased from 18.3 inches on 12 March (50% of normal to date) to 29.3 in on 18 March 2012 (76% of normal to date). Most of this 11 inch increase occurred in 4-5 days (13-17 March). 11 inch increase in 4-5 days = 22% of annual average 7 inch increase in 4 days = 14% of annual average

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12 Selected anomalous Reservoir water storage changes summer 2013 (roughly Jul-Sep) Lake Powell: 189,000 AF increase (300,000 AF if factor in normal decrease at this time) in 13 days ending 19 Sept (40% of actual storage increase from 2013 spring runoff; level rose 2.1 ft from 7-19 Sept; compared to ~5.0 ft rise from spring runoff 17 may 21 June 2013) Lake Mead: 61,000 AF increase in 2 weeks ending 19 Sept Salt River Project, AZ (6 lakes on Salt and Verde Rivers): 35,000 AF increase (60,000 AF if factor in normal decrease) since early August, kaf on 28 Aug to kaf on 19 Sept Elephant Butte + Caballo Lakes, NM (on the Rio Grande): 80,000 AF rise since early July (8 July lowest water level at Elephant Butte in 40 years; 60,000 AF). Denver Water Storage, CO: 20,000 AF increase in mid Sept storm (15-20% as much increase as from a normal spring runoff season). San Carlos Reservoir inflows vs outflows from about 22 Jul 19 Sept: 100,000 AF (70,000 AF in 20 days in Sept through 19 Sept) These add up to over 600,000 AF of increased water availability in the region in late summer.

13 Altitude MSL (km) Atmospheric River Observatory Plan view Rain shadow GPS satellite Wind direction in AR Mountains ARO 3 2 Wind profiler beam with 100-m vertical resolution S-PROF data up to 10 km MSL Orographic cloud and precipitation Snow level 1 0 Atmospheric River Ocean Controlling layer (upslope winds) Surface friction and barrier jet S-PROF precipitation profiler; surface met; disdrometer Rain shadow GPS-met receiver Wind profiler (915 or 449 MHz) 10-m surface meteorology tower 0-50 km between wind profiler/gps-met site and S-PROF precipitation profiler 13

14 Storm-total rainfall at CZD (mm) 91 AR events observed over 6 years Storm-total upslope water vapor flux at BBY (cm m/s)

15 Storm-total runoff on Austin Ck (millions of m 3 ) Storm-total rainfall at CZD (mm) 91 AR events observed over 6 years Storm-total upslope water vapor flux at BBY (cm m/s) Storm-total upslope water vapor flux at BBY (cm m/s)

16 Validation of AR Forecasts Results/Implications While overall occurrence well forecast out to 10 days, landfall is less well predicted and the location is subject to significant errors, especially at longer leads RMS Error in Forecast AR Landfall Location Errors in location increase to over 800 km at 10-day lead Errors in 3-5 day forecasts comparable with current hurricane track errors Model resolution a key factor From Wick et al., 2013 (in press) Models provide useful heads-up for AR impact and IWV content, but location highly uncertain Location uncertainty highlights limitations in ability to predict extreme precipitation and flooding Improvements in predictions clearly desirable

17 California has begun implementation of key land-based sensors Bodega Bay Atmos. River Observatory (ARO) was installed March 2013 An Atmospheric River-focused long-term observing network is being installed in CA as part of a 5-year project between CA Dept. of Water Resources (DWR), NOAA and Scripps Inst. Of Oceanography - Installed >100 field sites 17

18 Photo Credit: NASA

19 start GH AR Flight, Feb 2011, IVT end 403 km wide 186x10 6 kg/s flux ~11 Mississippis 10 Million Acre Feet/day

20 Atmospheric Rivers as Drought Busters Courtesy of Mike Dettinger Based on a scientific article that is accepted for publication

21 How do droughts end? I am going to define a persistent drought break as a month during which the PDSI changes from below -2 to above -2, and then stays above -2 for at least 6 months.

22 What is the PDSI doing (on average) in the months before & after these breaks?

23 Here are the long-term averages of the PDSI steps in all months when the PDSI went from below -2 to above -2. Average steps between 2 and 3 (like those we saw for the dashed curves in the preceding slide) are not uncommon.

24 Here is the corresponding map if we average over all of the historical months with DOWNWARD PDSI crossings, going from PDSI > -2 (wetter) to PDSI < -2 (drier). Notice that the color bar is different here. Distributions of average PDSI steps across PDSI=-2 at 344 climate divisions The average initial steps INTO drought are much smaller, everywhere, than the final steps OUT OF drought!

25 Thus, in all CONUS climate divisions, the average drought ends with a bang; the average drought begins with a whimper. Distributions of average PDSI steps across PDSI=-2 at 344 climate divisions

26 But for any given climate division (e.g., our SoCal coastal division), we can look at histograms of the PDSI steps across the PDSI=-2 threshold for ALL breaks, rather than looking only at long-term averages. In southern California coastal division, MOST droughts end in a big PDSI step (>2 PDSI units in a month). No droughts begin with steps that large. In Washington state, most droughts end in a similarly big PDSI step. No droughts begin with steps that large.

27 Thus, in (at least) SoCal, most (57-79%) droughts end with a bang; all droughts begins with a whimper.

28 Atmospheric rivers as drought busters on the West Coast Method: (1) I defined a persistent drought break as an occasion when PDSI rises from below -2 to above -2 in a given month, and stays above -2 for at least 6 months. (2) Then I used daily precipitation records to identify the largest storm in each of those drought-breaking months, since (3) Finally I looked at the Reanalysis integrated vapor transport fields associated with those largest storms, to determine what types of storms were responsible. Applications: I applied this analysis to: Washington State Oregon State Northern California (divisions 1&2) Central California (divisions 4&5) Southern California coastal division (6)

29 Resulting breakout of drought busters: Number of Persistent Drought Breaks, AR storms Non-AR breaks 0 Washington Oregon Northern Cal Central Cal Southern Cal 100% Percentage of Persistent Drought Breaks, % 60% 40% 20% AR storms Non-AR breaks 0% Washington Oregon Northern Cal Central Cal Southern Cal

30 Droughts on average--end with a bang & begin with a whimper all over CONUS Most droughts end with a bang & begin with a whimper in SoCal (at least) Atmospheric rivers provide the bang in a large fraction of the west coast drought breaks, especially in winters

31 Exploiting Drought Indicators Anne Steinemann Visiting Researcher and Program Manager Scripps Institution of Oceanography U.C. San Diego Professor Civil and Environmental Engineering, and Public Affairs University of Washington

32 Indicators and NIDIS NIDIS shall provide an effective drought early warning system that collects and integrates information on the key indicators of drought in order to make usable, reliable, and timely drought forecasts and assessments to engender better decisions thereby leading to reduced impacts and costs

33 What are Indicators? Variables that characterize drought conditions Examples: precipitation, streamflows, soil moisture, reservoir storage, groundwater levels, water deliveries, snowpack, Standardized Precipitation Index, not only hydrology also regulatory factors, etc. not only local / regional indicators also external conditions not only for monitoring also for forecasting

34 What are Triggers? Specific values of an indicator linked with drought responses Level Indicator Value Responses (percentiles) Mild Drought A... Moderate Drought B Severe Drought C Extreme Drought D

35 Why Indicators are Useful Provide early warning of drought Characterize drought conditions (severity, spatial extent, ) Compare with historic droughts Link drought levels with responses (triggers)

36 Even simple indicators are complex Precipitation Measured how? Over what spatial scale? Relative to what period of record? Stages of severity? Relevant to whom? What time period - anomaly?

37 What are "Good" Indicators? Stakeholder-Based Criteria consistent and comparable terms transparent, intuitive, actionable, trustworthy individual/separated but possible to combine and customize represent dry to wet conditions relevant to regional and local droughts consolidated, all in one place "one stop shopping" relative to historic drought conditions -> Percentiles

38 Need for Forecasts Water managers say "we need predictive information, especially seasonal to interannual forecasts" But "we don't use forecasts that are out there" "Very confusing I don't talk meteorologist talk" "Forecasts are high altitude" "Need greater level of trust so could be translated into mitigations and preparedness" "Wish we could have more confidence [in the forecasts], to ring the bell louder."

39 Analog Years Approach Compare current year conditions with prior years, looking for "matches" Indicators based on percentiles, and percentile categories Degree of similitude comparing categories Use analog year(s) to predict future conditions and trends "How is this year shaping up? Does it look similar to any of the previous years? If so, what happened?"

40 Considerations Criteria for determining an "analog year" Lagged, multiple, multi-month, omitted indicators Quantitative / qualitative assessments Period of record Statistical significance

41 Ongoing Work Consolidated source of monitoring data range of individual indicators, all in one place, customizable, comparable, percentile-based Usable forecast information regionally relevant, trustworthy, analog years databases and approaches Development, selection, and evaluation of indicators indicators (monitoring / forecasting) that provide effective early warning, assist decision-makers, and ultimately reduce drought impacts

42 Schematic illustration of regional variations in the primary weather phenomena that lead to extreme precipitation, flooding and contribute to water supply in the Western U.S. Atmospheric Rivers (fall and winter) Great Plains Deep Convection (spring and summer) Spring Front Range Upslope (rain/snow) Southwest Monsoon (summer & fall)

43 Thank you!