1. Alan F. Hamlet Eric P. Salathé Matt Stumbaugh Se-Yeun Lee Seshu Vaddey U.S. Army Corps of Engineers JISAO Climate Impacts Group Dept. of Civil and Environmental Engineering University of Washington Estimates of changing flood risk in the 21 st century Pacific Northwest based on regional scale climate model simulations

2. Floods

3. Evidence of Changing Flood Statistics

4. Role of Atmospheric Rivers in Flooding (Nov 7, 2006) Niemann, PJ, LJ Schick, FM Ralph, M Hughes, GA Wick, 2010: Flooding in Western Washington: The Connection to Atmospheric Rivers, J. of Hydrometeorology, (in review)

5. Effects of Projected Warming and Changing Monthly Precipitation Variability on 21 st Century Flood Risk

6. Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z 21 st Century Climate Impacts for the Pacific Northwest Region

7. Seasonal Precipitation Changes for the Pacific Northwest Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

8. Hybrid Delta Downscaling Method Performed for each VIC grid cell: Hist. Daily Timeseries Hist. Monthly Timeseries Historic Monthly CDF Bias Corrected Future Monthly CDF Projected Daily Timeseries 1916-2006 1970-1999 30 yr window 1916-2006 “Base Case”

9. 2040s Changes in Flood Risk Snohomish at Monroe A1BB1 Historical 10 Member Ensemble Using the Hybrid Delta Downscaling Approach

10. Relationship Between Change in Q100 and Winter Temp

11. Overview of Key Science Questions: Will daily precipitation statistics at smaller spatial scales change differently in response to global climate change than monthly precipitation statistics at large spatial scales? Will the nature of extreme storms (such as atmospheric rivers) change in response to global climate change? Will different areas of the PNW experience substantially different changes in extreme precipitation and flood statistics (e.g. the west slopes of the Cascades vs. the east slopes)? Will the seasonal timing of flood events change?

12. Improving Flood Risk Projections Using High Resolution Regional Climate Models

13. Regional Climate Modeling at CIG  WRF Model (NOAH LSM) 36 to 12 km  ECHAM5 forcing  CCSM3 forcing (A1B and A2 scenarios)  HadRM 25 km  HadCM3 forcing

14. Role of Atmospheric Rivers in Flooding (Nov 7, 2006) Niemann, PJ, LJ Schick, FM Ralph, M Hughes, GA Wick, 2010: Flooding in Western Washington: The Connection to Atmospheric Rivers, J. of Hydrometeorology, (in review)

15. Snohomish River Near Monroe, WA

16. Downscaling

17. WRF output is first regridded to 1/16 th degree Then, for each VIC grid cell: WRF Daily Downscaling Method WRF Daily Time Series WRF Daily CDF Historical VIC Daily CDF Bias Corrected Daily Time Series 1970-1999 2040-2069 1970-1999 2040-2069 1970-1999 The storm size distribution and time series behavior of the simulations comes directly from the daily WRF simulations.

18. Preliminary Results for the ECHAM5 A1B Sceario for the 2050s.

19. Chehalis River at Porter Daily Peak Flow (cfs) Date of Peak Flow (1 = Oct 1) Probability of Exceedence ECHAM5 2050 A1B

20. Sauk River near Sauk ECHAM5 2050 A1B Daily Peak Flow (cfs) Date of Peak Flow (1 = Oct 1) Probability of Exceedence

21. Boise River at Boise ECHAM5 2050 A1B Daily Peak Flow (cfs) Date of Peak Flow (1 = Oct 1) Probability of Exceedence

22. Columbia River at The Dalles Daily Peak Flow (cfs) Date of Peak Flow (1 = Oct 1) Probability of Exceedence ECHAM5 2050 A1B

23. Conclusions: Our initial exploration of changing flood risk in the PNW using statistical downscaling points to increasing flood risk in most areas of the region due to projected regional warming and increases in cool season precipitation. Regional climate models offer more physically based assessment tools for understanding the potential changes in nature of extreme storms (such as atmospheric rivers), the timing of flooding, and a potentially improved picture of the spatial variations in changing hydrologic extremes across the region. Initial results suggest more extreme storms in the early fall and general increases in flood intensity will accompany global climate change in the PNW. In particular, many sites show distinct shifts towards flooding earlier in the water year due to the combination of changes in snowpack and earlier storms.

24. Extras

25. Hybrid Downscaling Method Performed for each VIC grid cell: Hist. Daily Timeseries Hist. Monthly Timeseries Historic Monthly CDF Bias Corrected Future Monthly CDF Projected Daily Timeseries 1916-2006 1970-1999 30 yr window 1916-2006 “Base Case”

26. Daily Precipitation (mm) Day of Month Monthly to Daily Precipitation Scaling SeaTac. Feb, 1996, hypothetical 30% Increase