1. Implications of 21st century climate change for the hydrology of Washington October 6, 2009 CIG Fall Forecast Meeting Climate science in the public interest UW Climate Impacts Group Marketa M Elsner 1 with Lan Cuo 2, Nathalie Voisin 3, Jeffrey S Deems 4, Alan F Hamlet 1,3, Julie A Vano 3, Kristian EB Mickelson 5, Se-Yeun Lee 3, and Dennis P Lettenmaier 1,3 1) CSES Climate Impacts Group, University of Washington, Seattle, WA 2) Pacific Climate Impacts Consortium, University of Victoria, BC 3) Dept. of Civil and Environmental Engineering, University of Washington, Seattle, WA 4) Western Water Assessment & National Snow and Ice Data Center, Boulder, CO 5) U.S. Army Corps of Engineers, Seattle District

3. Focus is climate change impacts on Washington, but this requires attention to regional climate, hydrology, ecosystems, and economies. Project Study Region

4. CO 2 Annual Emissions Raupach et al. 2007, PNAS 2006 2007 CDIAC updated emissions CDIAC = Carbon Dioxide Information Analysis Center, Oak Ridge National Lab (DOE)

5. Global Climate Models 2 different emissions scenarios 20 models using A1B (medium scenario) 19 models using B1 (low scenario) Downscaled to regional projections of P and T for the 2020s, 2040s, 2080s Hydrologic Models Projections of future changes in snowpack, streamflow, soil moisture, etc. Energy Water ManagementForestsAgriculture Salmon Infrastructure Health Regional Climate Models Analyzed changes in extreme events

6. Projected Increases in PNW Temp Changes relative to 1970-1999 7.2° F 3.6° F 0°F 10.8°F 14.4°F +2.2ºF (1.1-3.4ºF) +3.5ºF (1.6-5.2ºF) +5.9ºF (2.8-9.7ºF) °C°C Rate of change per decade expected to be 3x greater through mid-21 st century Choice of emissions scenario matter more after 2040s Mote and Salathé, 2009

7. Projected Changes in Annual Precipitation * Compared with 1970-1999 average Changes in annual precipitation averaged over all models are small (+1-2%) but some models show large seasonal changes, especially toward wetter autumns and winters and drier summers. Mote and Salathé, 2009

8. Large Scale Model (VIC) ~12mi 2 per cell Hydrologic Simulations Fine Scale Model (DHSVM) ~6 acres per cell Common two-layer snow algorithm - top layer used to solve an energy balance with the atmosphere - bottom layer is used as storage to simulate deeper snowpack

9. Climate Change Projections - hydrology (using “delta method”) 39 Climate Change Scenarios - each is a monthly timeseries of P and T from 2000-2099 3 chosen projection windows 200020502100 Mean  P &  T for 2020s (2010-2039) Mean  P &  T for 2040s (2030-2059) Mean  P &  T for 2080s (2070-2099) Historical daily timeseries (1916-2006) perturbed by mean monthly  P &  T (same mean  P and  T applied to each day in a given month) New daily timeseries which incorporates historical daily patterns and future projections of precipitation and temperature

10. Elsner, M.M. et al. 2009 Low Medium -29%-44%-65% -53%-37%-27% * Compared with water year 1917-2006 historical mean

11. Projected Changes in April 1 SWE by Elevation (A1B Medium Scenario) * Compared with water year 1917-2006 historical mean Elsner, M.M. et al. 2009 -37% -17% -54% -42% -29% -71% -63% -54% -27%

12. Weekly Snowpack Projections Low (B1)Medium (A1B) Low (B1)Medium (A1B) Cedar River Yakima River

13. Chehalis River At Porter Columbia River at The Dalles Yakima River at Parker

14. Impacts to Streamflow Timing Historical and Projected 21 st Century Flows for the A1B Scenario Mixed Rain/SnowRain DominantSnowmelt Dominant Yakima RiverChehalis RiverColumbia River No significant change, however, western WA flood magnitudes will likely increase due to warming + more intense winter storms. More precipitation falls as rain instead of snow, leading to an increase in flooding in winter and decrease in spring and summer even if precipitation remains the same Increased winter flow, earlier and reduced peak flow, lower summer flows

15. Weekly Streamflow Projections Cedar River - inflow to Chester Morse Reservoir Yakima River at Parker

16. Key Conclusions For Washington, April 1 snowpack is projected to decrease: –27% to 29% by the 2020s - low (B1) and medium (A1B) scenario –37% to 44% by the 2040s -low (B1) and medium (A1B) scenario –53% to 65% by the 2080s -low (B1) and medium (A1B) scenario Annual runoff across the state may see modest increases and these changes are mainly driven by projected increases in winter precipitation. Sensitive watersheds (e.g. Yakima and Puget Sound basins) are projected to see greater decreases in snowpack and significant changes in seasonal streamflow due to significant changes in the rain/snow balance

17. Thank you! Marketa McGuire Elsner mmcguire@uw.edu JISAO CSES Climate Impacts Group www.cses.washington.ed/cig Climate science in the public interest UW Climate Impacts Group

18. Seasonal Projected Temperature Changes Over the PNW

19. Seasonal Projected Precipitation Changes Over the PNW

20. Mantua et al. 2009

21. Changes in Flood Risks Floods in western WA will likely increase in magnitude due to the combined effects of warming and increasingly intense winter storms. In other parts of the State, changes in flooding are mixed, and in eastern WA projected reductions in spring flood risk are common due to loss of spring snow cover. Mantua et al. 2009, Elsner et al. 2009 Mixed Rain/SnowRain Dominant Yakima River (Eastern WA)Chehalis River (Western WA)