Climate, Drought, and Change Michael Anderson State Climatologist. Managing Drought Public Policy Institute of California January 12, 2015

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1 Climate, Drought, and Change Michael Anderson State Climatologist Managing Drought Public Policy Institute of California January 12, 2015 Oroville Reservoir January 2009

2 Presentation Overview The Rules What is Happening? Signs of Change Folsom Reservoir January 2014

3 California s topography is important to our weather and climate

4 10 8 Station Precipitation Index (Inches) Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Sacramento River Flow (MAF) Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Period of Record Monthly Averages

5 California s precipitation is uniquely variable Std Dev of Annual Precipitation Mean Annual Precipitation Higher values are higher variability Source: Dettinger et al (2011)

6 Just a few storms each year are the core of California s water supplies Source: Dettinger et al (2011)

7 Atmospheric rivers are a key phenomenon affecting water supply and flooding Storm Track changes Polar Processes Cyclogensis L Flooding & water supply MJO/Tropical Convection Easterly Wave ENSO The size of an atmospheric river results from the alignment of key processes The absence of atmospheric river activity important to drought (Dettinger and Cayan, 2014) Slide adapted from M. Ralph

8 Decadal scale precipitation variability tied to atmospheric river landfall variability Source: Dettinger and Cayan (2014)

9 Water vapor thresholds are important to precipitation processes Values in cm Values in cm 12/27/2013 1/29/2014

10 Presentation Overview The Rules What is Happening? Signs of Change Folsom Reservoir January 2014

11 Using the Northern Sierra 8 Station Index Water Year Precipitation, inches Water Year Annual Average: 50 inches Maximum Year (1983): 88.5 inches Minimum Year (1924): 17.1 inches Period of Record Present 9 of 14 years of 21 st Century below average Average of: Mt. Shasta City Shasta Dam Mineral Brush Creek RS Quincy Sierraville RS Pacific House Blue Canyon

12 was the 8th driest water year on record

13 driest 3-Year period for CA

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16 Surface reservoir storage since Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec California reservoir storage, million acre-feet Avg Source: California Department of Water Resources Slide from B. Rippey, USDA

17 Recent rains have helped, but most reservoirs are still below average October 2014 January 2015 Source: DWR, California Data Exchange Center

18 Presentation Overview The Rules What is Happening? Signs of Change Tenaya Lake

19 Climate change expectations Warmer temperatures Smaller snowpack/more rain, less snow Earlier snowmelt onset More variability More extremes Are we seeing these already?

20 21 st Century breakdown so far: A lot of variability station index POR Average: 50 inches : 53 inches 21 st Century: 49 inches Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Period of Record st Century Note WY 2012 was 3 rd driest December (0.34 ) and WY2014 was 4 th driest (0.80 )

21 Variability also evident in Sacramento River runoff Runoff, thousand acre-feet (taf) Sacramento River runoff POR Average: 18.3 MAF POR Average: 17,823 taf : 18.8 MAF : 18,827 taf 21 st Century: 16.1 MAF 21 st Century: 16,068 taf Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep POR st Century

22 It s getting warmer, which increases the impact of droughts Annual Precipitation (inches) Precipitation and temperature: Annual Mean Temperature (degrees F) Source: NOAA Climate Division 2 Calendar Year Data

23 21 st Century droughts on the Sacramento River 40 Water Year Runoff (million acre-feet) of 20 lowest April-July flows since th Century 21st Century POR Average April July Runoff (million acre-feet)

24 Western Region Climate Center s CA Climate Tracker: A way to track change Source: California Climate Tracker - WRCC

25 Spatial representation of temperature rankings for water year 2014 Source: California Climate Tracker - WRCC

26 Summarizing thoughts Current drought and other 21 st Century droughts have shown record-setting characteristics and are warmer than 20 th Century counterparts. Atmospheric river events provide significant inputs into annual precipitation totals. There are fewer such events in drought years, and characteristics of atmospheric events will change with climate change.

27 Summarizing thoughts Planning for future droughts can take advantage of information in the historical record, including paleo reconstructions. The trick will be to increase our understanding of causal mechanisms and watershed condition/response over different time scales. Averages are not so useful anymore. We need to understand variability and process.