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

1. Understanding the Effects of Climate Change and Climate Variability on River Recreation in the Pacific Northwest • Alan F. Hamlet, • Philip W. Mote, • Dennis P. Lettenmaier • 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. 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

4. 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

5. Natural AND human influences explain the observations of global warming best. Natural Climate Influence Human Climate Influence All Climate Influences

6. +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

7. % +6% +2% +1% Observed 20th century variability -1 to +3% -1 to +9% -2 to +21% Pacific Northwest

8. Hydroclimatology of the Pacific Northwest

9. Annual PNW Precipitation (mm) Winter climate in the mountains is the key driver of streamflow. Snowpack functions as a natural reservoir. Elevation (m)

10. Hydrologic Characteristics of PNW Rivers

11. Effects of the PDO and ENSO on Columbia River Summer Streamflows PDO Cool Cool Warm Warm high high low low

12. Warming Affects Streamflow Timing • Temperature warms, • precipitation unaltered: • Streamflow timing is altered • Annual volume may be somewhat lower due to increased ET Black: Obs Red: 2.3° C warming

13. Precipitation Affects Streamflow Volume • Precipitation increases, • temperature unaltered: • Streamflow timing stays about the same • Annual volume is altered Black -- Obs Blue -- 9% increase in precip.

14. Hydrologic Impacts for the PNW

15. Schematic of VIC Hydrologic Model and Energy Balance Snow Model 6 km 1/16th Deg. PNW 6 km Snow Model

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

17. 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

18. 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

19. Chehalis River

20. Hoh River

21. Nooksack River

22. Skagit River

23. Decadal Climate Variability and Climate Change

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

25. Regionally Averaged Cool Season Precipitation Anomalies PRECIP

26. Some Implications for River Recreation

27. Warming May Improve Fall and Winter Flow Conditions and May Require Additional Use of Storage to Maintain Existing Flow Regimes in Summer.

28. Increased Demand + Reduced Supply = Competition • Increasing population and systematic reductions in summer water supplies are likely to increase competition between different uses and users of water in the West. • Such changes will force water resources management agencies to make complex and contentious tradeoffs between conventional water resources objectives such as water supply, flood control and hydropower production and river recreation. • Different systems may respond very differently (e.g. for different storage to flow ratios)

29. Implications for Hydropower Licensing Agreements • Because of the long time frame of hydropower licensing agreements, considerable changes in climate and streamflow are likely to occur during the life of the license. • These changes will tend to “unbalance” existing tradeoffs between water resources objectives such as hydropower, flood control, water supply, instream flow, and water temperature. Different users and uses of water will not be impacted equally. As warming progresses, water management plans will need to be updated regularly to cope with what we believe will be rapidly evolving conditions. • If current licensing agreements are not robust to these expected hydrologic changes and do not include flexible mechanisms for updating the agreements, law suits or other challenges to the license may be the only options as warming progresses. • To cope with these issues, new tools and approaches are needed to create licensing agreements that can adapt autonomously to changing hydrologic conditions and “rebalance” tradeoffs between different uses in a well defined and agreed upon manner. Such approaches are technically feasible.

30. 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.

31. Conclusions: Global climate change is expected to result in important hydrologic changes in western rivers because of impacts to snowpack and streamflow timing. Winter flows are expected to increase and summer flows to decline. Some important climate change impact pathways related to river recreation include: impacts to summer water supply and streamflow augmentation, increasing competition for water resources in summer, and the disruption of existing coordination agreements. Adaptation to a changing climate may mean a shift in the seasonality of river recreation opportunities from summer to winter.