Climate Change Impacts on Western U.S. Hydrology

1. Hydrologic Implications of Climate Change for the Western U.S. and the Columbia River Basin • Alan F. Hamlet • JISAO/CSES Climate Impacts Group • Dept. of Civil and Environmental Engineering • University of Washington

2. Climatological Foundation of U.S. Water Resources Planning and Management: 1) Risks are stationary in time. 2) Observed streamflow records are the best estimate of future variability. 3) Systems and operational paradigms that are robust to past variability are robust to future variability.

3. The Myth of Stationarity Meets the Death of Stationarity 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

4. Global Climate Change Scenarios and Hydrologic Impacts for the PNW

5. 1) 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.

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

7. +3.2°C °C +1.7°C +0.7°C 1.2-5.5°C 0.9-2.4°C Observed 20th century variability 0.4-1.0°C Pacific Northwest

8. % -1 to +3% +6% +2% +1% Observed 20th century variability -2 to +21% -1 to +9% Pacific Northwest

9. Will Global Warming be “Warm and Wet” or “Warm and Dry”? Answer: Probably BOTH! Natural Flow Columbia River at The Dalles

10. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

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

12. The warmer locations are most sensitive to warming 2060s +2.3C, +6.8% winter precip

13. Cool Season Climate of the Western U.S. PNW GB CA CRB DJF Temp (°C) NDJFM Precip (mm)

14. 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

15. Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin (% change relative to current climate) 20th Century Climate “2040s” (+1.7 C) “2060s” (+ 2.25 C) -3.6% -11.5% -21.4% -34.8% April 1 SWE (mm)

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. Chehalis River

18. Hoh River

19. Nooksack River

20. Mapping of Sensitive Areas in the PNW by Fraction of Precipitation Stored as Peak Snowpack HUC 4 Scale Watersheds in the PNW

21. Climate Change Impacts are Similar to Impacts of Water Management in PNW Hydropower Systems Estimated natural flows Skagit River at Mt. Vernon

22. Changes in Flood Risk in the Western U.S.

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

24. 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

25. Landscape Scale Ecosystem Impacts

26. 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)

27. Temperature thresholds for coldwater fish in freshwater • Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region • A monthly average temperature of 68ºF (20ºC) has been used as an upper limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing +2.3 °C +1.7 °C

28. 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.

29. Impacts to Managed Resources in the Columbia River Basin

30. Some Conflicting Objectives Likely to be Impacted by Climate Change: • Hydropower and water supply vs. flood control • Hydropower and water supply vs. instream flow and ecosystem services. • Interstate and international transboundary agreements

32. Impacts on Columbia Basin hydropower supplies • Winter and Spring: increased generation • Summer: decreased generation • Annual: total production will depend primarily on annual precipitation (+2C, +6%) (+2.3C, +5%) (+2.9C, -4%) NWPCC (2005)

33. Temperature Effects on Demand

34. Managed Flow Augmentation • The flow needed to provide acceptable flow velocity for juvenile transport is frequently higher than natural flow, particularly in late summer (I.e. use of storage is required). Climate change increases the amount of storage required to meet flow targets. • Currently very little storage is allocated to fish in comparison with hydropower. • In a conflict between hydro or irrigation and fish flow, the current reservoir operating policies are designed to protect hydro and irrigation (fish flow storage allocation for main stem and Snake River flow targets is at the top of a shared reservoir storage pool) • The Columbia River Treaty does not provide explicitly for summer flow in the U.S. (transboundary issues). Compare with guaranteed winter releases associated with flood control. Hydro storage Fish flow storage

35. Monthly time step ColSim simulations show that unless significant changes in reservoir operations are put in place, regulated streamflow feeding the Hanford Reach is likely to be severely impacted in July and August.

36. Adaptation to climate change will require complex tradeoffs between ecosystem protection and hydropower operations Source: Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change, Vol. 62, Issue 1-3, 233-256

37. Temperature thresholds for coldwater fish in freshwater • Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region • A monthly average temperature of 68ºF (20ºC) has been used as an upper limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing +2.3 °C +1.7 °C

38. Implications for Transboundary Water Management in the Columbia Basin • Climate change will result in significant hydrologic changes in the Columbia River and its tributaries. • Snowpack in the BC portion of the Columbia basin is much less sensitive to warming in comparison with portions of the basin in the U.S. and streamflow timing shifts will also be smaller in Canada. • As warming progresses, Canada will have an increasing fraction of the snowpack contributing to summer streamflow volumes in the Columbia basin. • These differing impacts in the two countries have the potential to “unbalance” the current coordination agreements, and will present serious challenges to meeting instream flows on the U.S. side. • Changes in flood control, hydropower production, and instream flow augmentation will all be needed as the flow regime changes.

39. Some Thoughts on Climate Change Adaptation • in the Columbia Basin • In 1975 the Columbia basin’s operating system was state of the art. 30 years later, the basin’s operating plan is both out of date and struggling to keep pace with the many changes in the basin. • Do the current water resources policies and transboundary agreements in the Columbia basin have the scope and flexibility needed to cope with a changing basin, a rapidly evolving climate system, and increasing human populations? If not, how can we effectively reduce the Columbia’s vulnerability to these changes? • Are changes in the margins of the Columbia’s current reservoir operating policies going to be sufficient?

40. 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.