Alan F. Hamlet, Philip W. Mote, Dennis P. Lettenmaier JISAO/CSES Climate Impacts Group

1. Effects of Climate Change on Water Resources in the Pacific Northwest and Western U.S. • Alan F. Hamlet, • Philip W. Mote, • Dennis P. Lettenmaier • JISAO/CSES Climate Impacts Group • Dept. of Civil and Environmental Engineering • University of Washington

2. Example of a flawed water planning study: The Colorado River Compact of 1922 The Colorado River Compact of 1922 divided the use of waters of the Colorado River System between the Upper and Lower Colorado River Basin. It apportioned **in perpetuity** to the Upper and Lower Basin, respectively, the beneficial consumptive use of 7.5 million acre feet (maf) of water per annum. It also provided that the Upper Basin will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 7.5 maf for any period of ten consecutive years. The Mexican Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 maf. **These amounts, when combined, exceed the river's long-term average annual flow**.

3. What’s the Problem? Despite a general awareness of these issues in the water planning community, there is growing evidence that future climate variability will not look like the past and that current planning activities, which frequently use a limited observed streamflow record to represent climate variability, are in danger of repeating the same kind of mistakes made 85 years ago in forging the Colorado River Compact. Long-term water supply planning and specific agreements influenced by this planning (e.g. water allocation agreements) should be informed by the best and most complete climate information available, but frequently they are not.

4. 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

5. +3.2°C °C +1.7°C +0.7°C 1.2-5.5°C 0.9-2.4°C 0.4-1.0°C Observed 20th century variability Pacific Northwest

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

7. Will Global Warming be “Warm and Wet” or “Warm and Dry”? Answer: Probably BOTH!

8. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

9. Hydrologic Changes Associated with Warming

10. Hydrologic Characteristics of PNW Rivers

11. The warmest locations that accumulate snowpack are most sensitive to warming +2.3C, +6.8% winter precip

12. 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)

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

14. Sensitivity of a Transient Snow Basin Nooksack River

15. Sensitivity of a Rain Dominant Basin Chehalis River

16. 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

17. As the West warms, spring flows rise and summer flows drop Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow timing across western North America, J. Climate, 18 (8): 1136-1155

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

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

20. 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

21. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

22. 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

23. Water Supply Impacts

24. Water Supply Impact Pathways Reductions in Supply Climate Change Combined Impacts Increases in Demand Increasing Population Conflicts with Other Water Resources Objectives

25. Transient SWE simulation from HadCM3 (A2) GCM run (with running 10 year average smoothing) • Simulated from observed climate shows a declining trend of ~3KAF per decade (1935-2000) • HadCM3 simulated declines ~4KAF per decade Figure courtesy of Matt Wiley and Richard Palmer at CEE, UW

26. In sensitive areas, systematic reductions in summer water availability will affect the yield of water supply systems. Master's Thesis: Wiley, M.W. (2004). "Analysis Techniques to Incorporate Climate Change Information into Seattle’s Long Range Water Supply Planning," University of Washington

27. Changes in Hydropower Resources

28. 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)

29. Warming climate impacts on electricity demand • Reductions in winter heating demand • Small increases in summer air conditioning demand in the warmest parts of the region NWPCC 2005

30. Climate change adaptation may involve complex tradeoffs between competing system objectives 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

31. Flood Control vs Reservoir Refill

32. Flood Control vs. Refill : Current Climate Full

33. Flood Control vs. Refill : Current Climate : + 2.25 oC No adaption Streamflow timing shifts can reduce the reliability of reservoir refill + 2.25 oC Full

34. Flood Control vs. Refill : Current Climate : + 2.25 oC No adaption : + 2.25 oC plus adaption Streamflow timing shifts can reduce the reliability of reservoir refill + 2.25 oC Full

35. Instream Flow Augmentation and Water Quality

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

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 air 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 +1.7 °C +2.3 °C

38. Conclusions: Global climate change is expected to result in significant hydrologic changes in the PNW and western U.S. because of widespread impacts to snowpack and streamflow timing. Some important water resources impact pathways include: reductions in summer water supply, changes in the seasonality of hydropower resources, disruption in the balance between flood control and reservoir refill, increased need for streamflow augmentation, and impacts to water quality (particularly temperature). These climate-related impacts will force difficult tradeoffs between competing water resources objectives in an already conflicted policy arena.

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.