1. Washington State Climate Change Impacts Assessment: Implications of 21 st century climate change for the hydrology of Washington Marketa M Elsner 1 with Lan Cuo 2, Nathalie Voisin 2, Jeffrey S Deems 2, Alan F Hamlet 1,2, Julie A Vano 2, Kristian EB Mickelson 2, Se-Yeun Lee 2, and Dennis P Lettenmaier 1,2 1) Center for Science in the Earth System, Climate Impacts Group, University of Washington, Seattle, WA 98195 2) Dept. of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195 Climate science in the public interest

2. Overview Approach –incorporating climate change information into modeling Hydrologic Simulations –Models, their inputs, climate change projections –Focus watersheds Findings –Washington and focus watersheds Conclusion

3. Assessment Overview: Study Region

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

6. Large Scale Model (VIC) ~12mi 2 per cell Hydrologic Simulations Fine Scale Model (DHSVM) ~6 acres per cell

7. Climate Change Projections (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

8. Focus Watersheds Columbia River –Washington portion Puget Sound –Green River –Snohomish River –Cedar River –Tolt River Yakima River

9. Implications of 21 st century climate change on Washington’s watersheds

10. Elsner, M.M. et al. 2009: Implications of 21 st Century climate change for the hydrology of Washington State (in review) Low Medium

11. Yakima River Basin LowMedium

12. S.F. Tolt River Green River Sultan River Cedar River Puget Sound April 1 Snowpack (Snow Water Equivalent) Results shown are for medium (A1B) emissions scenario

13. Weekly Snowpack Projections Cedar River Yakima River LowMedium LowMedium

14. Elsner, M.M. et al. 2009: Implications of 21 st Century climate change for the hydrology of Washington State (in review)

16. Rain Dominant Watershed Monthly Streamflow Projections

17. Transient Rain-snow Watershed Monthly Streamflow Projections

18. Snowmelt Dominant Watershed Monthly Streamflow Projections

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

20. Key Conclusions Snowpack & Soil Moisture For Washington, April 1 snowpack (important indicator of summer water supply) is projected to decrease: –28% to 29% by the 2020s - low (B1) and medium (A1B) scenario –38% to 46% by the 2040s -low (B1) and medium (A1B) scenario –56% to 70% by the 2080s -low (B1) and medium (A1B) scenario *Sensitive watersheds (e.g. Yakima and Puget Sound basins) are projected to see greater decreases in snowpack For Washington, July 1 soil moisture is projected to decrease: –38th to 43rd percentile by the 2020s - low (B1) and medium (A1B) scenario –35th to 40th percentile by the 2040s - low (B1) and medium (A1B) scenario –32nd to 35th percentile by the 2080s - low (B1) and medium (A1B) scenario *50% being equal to mean historical values.

21. Key Conclusions Streamflow & Runoff Rivers will respond to climate change differently, depending on the balance of rain versus snow For Washington as a whole, projected changes in runoff (water into streams) depend strongly on season. –Average cool season (October to March) runoff is projected to increase 12% by the 2020s, 19% by the 2040s, and 31% by the 2080s –Average warm season (April to September) runoff is projected to decrease 18% by the 2020s, 24% by the 2040s, and 39% by the 2080s –Annual runoff across the state may see modest increases and these changes are mainly driven by projected increases in winter precipitation.

22. The Climate Impacts Group www.cses.washington.ed/cig Marketa McGuire Elsner mmcguire@u.washington.edu For more information:

23. Climate Change Projections Hydrologic Models Regional Climate Change Scenarios 20 GCMs 2 SRES Scenarios – A1B (medium) & B1 (low) ------------------------- 39 Total CC Scenarios (Monthly Time Series) Global Climate Models 1.Delta Method Approach Daily Time Series of Perturbed Historical Record (1915-2006) 2.Bias Correction & Statistical Downscaling (BCSD) Daily Time Series of Future Record (2001-2099) VIC (5km latitude x 6km longitude grid) DHSVM (150m grid)

24. Delta Method Advantages Address impacts of historical climate variability Realistic daily time series and spatial variability Many realizations of variability for each scenario Challenges Do not incorporate future climate variability introduced by GCMs BCSD Advantages Incorporate future climate variability projected by GCMs Facilitates trend analysis Challenges Current method may introduce unrealistic daily climate Inherits weaknesses of specific GCMs Climate Change Projections

25. 122 in 0.2 in 75% of annual precipitation (P) in the Cascades falls between October and March