Alan F. Hamlet JISAO/CSES Climate Impacts Group Dept. of Civil and Environmental Engineering

1. Hydrologic Implications of Climate Change for the Pacific Northwest and Washington State • Alan F. Hamlet • JISAO/CSES Climate Impacts Group • Dept. of Civil and Environmental Engineering • University of Washington

2. Recession of the Muir Glacier Aug, 13, 1941 Aug, 31, 2004 Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia http://nsidc.org/data/glacier_photo/special_high_res.html

3. Global Climate Change Scenarios for the PNW

4. 1) Global climate modeling experiments reproduce history of global temperatures remarkably well. 2) Natural forcings (e.g. volcanic eruptions and variations in solar radiation) alone cannot explain the rapid rise in temperature at the end of the 20th century.

5. Consensus Forecasts of Temperature and Precipitation Changes from IPCC AR4 GCMs

6. 21st Century Climate Impacts for the Pacific Northwest Region Mote, P.W. and E. P. Salathe Jr., 2009: Future climate in the Pacific Northwest (in review)

7. Snowpack

8. Schematic of VIC Hydrologic Model and Energy Balance Snow Model Snow Model

9. Trends in April 1 SWE 1950-1997 Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): 39-49

10. Overall Trends in April 1 SWE from 1947-2003 DJF avg T (C) Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561

11. Temperature Related Trends in April 1 SWE from 1947-2003 DJF avg T (C) Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561

12. Precipitation Related Trends in April 1 SWE from 1947-2003 DJF avg T (C) Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561

13. Plotting Areas of High Hydrologic Disturbance Elsner et al., 2009: Implications of 21st Century climate change for the hydrology of Washington State (in review)

14. Change in Long-Term Mean April 1 SWE in WA -29% -27% -44% -37% -65% -53% Elsner et al., 2009: Implications of 21st Century climate change for the hydrology of Washington State (in review)

15. Changes in Seasonal Streamflow Timing

16. Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming • Impacts: • Increased winter flow • Earlier and reduced peak flows • Reduced summer flow volume • Reduced late summer low flow

17. Projected Streamflow Timing Shifts in Washington

18. Historical and Projected 21st Century Flows for the A1b Scenario Chehalis River

19. Historical and Projected 21st Century Flows for the A1b Scenario Quinault River

20. Historical and Projected 21st Century Flows for the A1b Scenario Elwah River

21. Historical and Projected 21st Century Flows for the A1b Scenario Skagit River

22. Historical and Projected 21st Century Flows for the A1b Scenario Yakima River

23. Climate Change Will Result in Widespread Transformation of Snowmelt and Transient Watersheds to Rain Dominant Watersheds Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review)

24. Changes in Extreme Precipitation

25. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

26. Observed Changes in Extreme Precipitation Intensity for Seatac Airport Rosenburg et al., 2009: Precipitation Extremes and the Impacts of Climate Change on Stormwater Infrastructure in Washington State, (in review)

27. Projected Changes in Precipitation Intensity (annual precip. divided by number of wet days) Salathé E. P. .Jr. , L. R. Leung, Y. Qian , and Y. Zhang, 2009: Regional Climate Model Projections for the State of Washington (in review)

28. Changes in Hydrologic Extremes

29. Regionally Averaged Temperature Trends Over the Western U.S. 1916-2003 Tmax PNW GB CA CRB Tmin

30. Simulated Changes in the 20-year Flood Associated with 20th Century Warming DJF Avg Temp (C) X20 2003 / X20 1915 DJF Avg Temp (C) X20 2003 / X20 1915 X20 2003 / X20 1915

31. 20-year Flood for “1973-2003” Compared to “1916-2003” for a Constant Late 20th Century Temperature Regime DJF Avg Temp (C) X20 ’73-’03 / X20 ’16-’03 X20 ’73-’03 / X20 ’16-’03

32. Summary of Flooding Impacts Rain Dominant Basins: Possible increases in flooding due to increased precipitation intensity, but no significant change from warming alone. Mixed Rain and Snow Basins Along the Coast: Strong increases due to warming and increased precipitation intensity (both effects increase flood risk) Inland Snowmelt Dominant Basins: Relatively small overall changes because effects of warming (decreased risks) and increased precipitation intensity (increased risks) are in the opposite directions.

33. Future Projections of Flood Risk in Washington • Floods in western WA are expected to 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 smaller, and in eastern WA projected reductions in flood risk are common due to loss of spring snow cover. Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review)

34. Changes in Low Flow Risks 7Q10 values are projected to systematically decline in western WA due to loss of snowpack and projected dryer summers Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review)

35. Landscape Scale Disturbance

36. 9.0 2005 8.0 7.0 2004 6.0 5.0 Annual area (ha × 106) affected by MPB in BC 2003 4.0 3.0 2.0 2002 1.0 2001 2000 1999 0 1910 1930 1950 1970 1990 2010 Year Bark Beetle Outbreak in British Columbia (Figure courtesy Allen Carroll)

37. Wide-Spread Glacial Retreat has Accompanied 20th Century Warming. Loss of glacial mass may increase summer flow in the short term and decrease summer flow in the long term. 1902 2002 The recession of the Illecillewaet Glacier at Rogers Pass between 1902 and 2002. Photographs courtesy of the Whyte Museum of the Canadian Rockies & Dr. Henry Vaux.

38. Adaptation

39. Approaches to Adaptation and Planning • Anticipate changes. Accept that the future climate will be substantially different than the past. • Use scenario based planning to evaluate options rather than the historic record. • Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach. • Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.