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

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. 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 more than 80 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. What’s the Problem?

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

5. Pacific Northwest °C 0.4-1.0°C 0.9-2.4°C 1.2-5.5°C Observed 20th century variability +1.7°C +0.7°C +3.2°C Until mid-century, emissions scenarios play a minor role in the temperature impacts. Towards the end of the century they play a big role. Conclusions: 1) Adaptation will be an essential component of the response to warming over the next 50 years. 2) Mitigation of greenhouse gas emissions will play an important role in determining the scope of late 21 st century impacts.

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

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

8. March 5, 2002 Collapse of the Larsen B Ice shelf, Antarctica

9. 1910 1930 1950 1970 1990 2010 0 0 1.0 2.0 3.0 4.0 5.0 6.0 Year 8.0 7.0 1999 2001 2000 2003 2002 Annual area (ha × 10 6 ) affected by MPB in BC 2005 9.0 2004 Bark Beetle Outbreak in British Columbia (Figure courtesy Allan Carroll)

11. Hydrologic Changes Associated with Warming

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

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

14. + 2.25 °C Climate change assessments using scenarios show significant hydrologic changes due to temperature in basins with substantial snow accumulation in winter. Naches River Basin on the East Slopes of the Cascades. 20 th Century Change

15. 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

16. 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 Trends in April 1 SWE 1950-1997

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. Water Supply Impacts

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

20. In Managed Systems the Storage to Flow Ratios are Important High Storage to Flow Ratio (e.g. the Colorado River basin) = Low sensitivity to streamflow timing shifts, high sensitivity to systematic changes in precipitation and multi-year drought Low Storage to Flow Ratio (e.g. the Seattle Water Supply System) = High sensitivity to streamflow timing shifts and changes in single year droughts.

21. 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

22. 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 In sensitive areas, systematic reductions in summer water availability will affect the yield of water supply systems.

23. Flood Control vs Reservoir Refill

24. Flood Control vs. Refill Full : Current Climate

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

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

27. Major U.S. Flood Control Checkpoints The Dalles Columbia Falls Bonners Ferry

28. Changes in Reservoir Storage : The Dalles Apr-Aug < 68 MAF : 68 <= The Dalles Apr-Aug <100 MAF : The Dalles Apr-Aug >=100 MAF  Greatest Improvement occurs in Mid flow years ( ) Se-Yeun Lee et al., 2007, Optimized Flood Control in the Columbia River Basin for a Global Warming Scenario, ASCE J. Water Resources Planning and Management (submitted)

29. Instream Flow Augmentation and Water Quality

30. 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

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

32. Temperature thresholds for coldwater fish in freshwater +1.7 °C +2.3 °C 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

33. Streamflow Forecasting Implications Loss of snowpack due to warming, and projected increases in precipitation variability may increase streamflow forecast uncertainties Statistical forecasting procedures may not be robust to new conditions related to vegetation changes or long term changes in ground water (need for alternative forecasting tools).

34. Sample Size = 270 years Super ensemble CDFs of PNW winter precipitation for four 30 year time slices from nine GCM simulations

35. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

36. Adaptation

37. Anticipate changes. Accept that the future climate will be substantially different than the past. Use scenario based planning to evaluate alternatives rather than the historic record. (Institutional challenges) Expect surprises and design for flexibility and robustness in the face of uncertain changes (particularly when sensitivity to precipitation changes dominates). Plan for the long haul. Where possible, make adaptive responses “self tending” to avoid repetitive costs of policy intervention as impacts increase over time. Approaches to Adaptation

38. Conclusions: Global climate change is expected to result in important hydrologic changes in the western U.S. because of impacts to snowpack and streamflow timing. Some important impact pathways related to USBR missions include: impacts to summer water supply, balance of flood control and reservoir refill, streamflow augmentation and water quality, streamflow forecasting uncertainty. Wide-spread institutional obstacles currently exist that would effectively prevent the use of scenario-based planning procedures, yet use of the historic streamflow record for risk assessment and long-range planning is expected to become increasingly problematic as the climate warms.