1. Alan F. Hamlet Philip W. Mote Martyn Clark Dennis P. Lettenmaier Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington May, 2005 Hydrological Impacts of Global Climate Change http://www.hydro.washington.edu/Lettenmaier/Presentations/2005/hamlet_WA_water_law_may_2005.ppt

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 planning and specific agreements influenced by this planning (such as the long-term licensing of hydropower projects and water permitting) should be informed by the best and most complete climate information available, but frequently they are not. What’s the Problem?

4. Annual PNW Precipitation (mm) Elevation (m)

5. Winter Precipitation Summer Precipitation (mm)

6. Hydrologic Characteristics of PNW Rivers

7. Temperature warms, precipitation unaltered: Streamflow timing is altered Annual volume stays about the same Precipitation increases, temperature unaltered: Streamflow timing stays about the same Annual volume is increases Sensitivity of Snowmelt and Transient Rivers to Changes in Temperature and Precipitation

8. Four Delta Method Climate Change Scenarios for the PNW ~ + 1.7 C ~ + 2.5 C Somewhat wetter winters and perhaps somewhat dryer summers

9. Snow Model Schematic of VIC Hydrologic Model and Energy Balance Snow Model PNW CA CR B GB

10. April 1 SWE (mm) Current Climate“2020s” (+1.7 C)“2040s” (+ 2.5 C) -44%-58% Changes in Simulated April 1 Snowpack for the Cascade Range in Washington and Oregon

11. + 2.5 °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.

12. Regulated Flow Historic Naturalized Flow Estimated Range of Naturalized Flow With 2040’s Warming Naturalized Flow for Historic and Global Warming Scenarios Compared to Effects of Regulation at 1990 Level Development Man-made storage ~ 30% of annual flow

13. Effects to the Cedar River (Seattle Water Supply) for “Middle-of-the-Road” Scenarios +1.7 C +2.5 C

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

15. Hydrologic Impacts for the Cascades

16. Obs. Summer Water Availability is Declining 55 years Figures courtesy of Matt Wiley and Richard Palmer at CEE, UW

17. Elevation (m) Cascades Sub Domain

18. Effects of Temperature And Precipitation Effects of Temperature Alone -19% -25% Trends in April 1 SWE for the WA and OR Cascades -2.84% per decade -2.15% per decade

19. Effects of Temperature And Precipitation Effects of Temperature Alone Trends in April 1 SWE for the WA and OR Cascades -35% -23% -4.25% per decade -6.48% per decade

20. 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

21. Conclusions Loss of snowpack is one of the most important impact pathways associated with global warming in the PNW. Hydrologic changes associated with warming include earlier and reduced peak snowpack, increased flows in winter, earlier and reduced spring and summer runoff, and decreased low flows in late summer. Large-scale changes in the seasonal dynamics of snow accumulation and melt have already occurred in the West. The most sensitive areas are coastal mountain ranges with relatively warm winter temperatures such as the Cascades

22. Broad Strategies for Incorporating Climate Variability and Climate Change in Long-Term Planning Identify and Assess Climate Linkages Identify potential linkages between climate and resource management that could affect outcomes in the long term. What’s being left out? Are there future “deal breakers” in these omissions? (e.g. ocean productivity, glaciers maintaining summer streamflow in the short term) Design for Robustness and Sustainability Use modeling studies to test preferred management alternatives for robustness in the face of climate variability represented by paleoclimatic studies, conventional observations, decadal variability, and future climate change projections. Identify Limits and Increase Response Capability Use estimates of uncertainties or “what if” scenarios to find the performance limits inherent in preferred management alternatives. How can response capability be increased? Expect Surprises and Design for Flexibility to Changing Conditions Design contingency planning into management guidelines to allow for ongoing adaptation to unexpected (or uncertain) conditions without recursive policy intervention.

23. Selected References and URL’s Climate Impacts Group Website http://www.cses.washington.edu/cig/ White Papers, Agenda, Presentations for CIG 2001 Climate Change Workshop http://jisao.washington.edu/PNWimpacts/Workshops/Skamania2001/WP01_agenda.htm Climate Change Streamflow Scenarios for Water Planning Studies http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm Refs on Climate Variability and Climate Change http://www.ce.washington.edu/~hamleaf/hamlet/publications.html