1. Climate Change: Impact on water in the western United States Tim P. Barnett David W. Pierce Scripps Institution of Oceanography La Jolla, CA

2. Effect of Climate Change on Western U.S. Large and growing population in a semi- arid region How will it impact water resources? Use an “end-to-end” approach

3. Project overview

4. Projected change in California snowfall...

5. Projected change by 2050

6. Downscaling: the motivation Global model (orange dots) vs. Regional model grid (green dots)

7. How good is the Hydrological Model? Andrew Wood, Univ. of Washington

8. River flow earlier in the year

9. Runoff already coming earlier

10. Columbia Basin Options Hydropower Or Salmon

11. California: Mandated water releases cannot be met

12. Colorado River: Not enough water to meet current demands

13. 10 million people in Los Angeles

14. Los Angeles water shortage Christensen et al., Climatic Change, to appear

15. Miss water treaty obligations to Mexico Christensen et al., Climatic Change, to appear

20. Ratio of chlorophyll concentration in spring, 2090s/2000s.

22. Step 1 Begin with current state of global oceans

23. Why initialize the oceans? That’s where the heat has gone Data from Levitus et al, Science, 2001

25. How good is the ocean simulation? Pierce et al, Climatic Change, to appear

26. Step 2 Estimate climate change due to emissions

27. Global Climate Change Simulation Parallel Climate Model (PCM) Business as Usual Scenario (BAU) 1860-2100 Estimate Western U.S. climate change

28. How well does the PCM work over the Western United States? Dec-Jan-Feb total precipitation (cm)

29. Step 3 Downscaling and impacts

30. How good is downscaling? El Nino rainfall simulation ObservationsDownscaled modelStandard reanalysis Ruby Leung, PNNL

31. Results Reduced snow cover Earlier snow melt Earlier spring flood crest Shift in ‘Run off” season Small rainfall reductions

32. Columbia River basin

33. Columbia River flow Andrew Wood, Univ. of Washington

34. Sacramento/San Joaquin River basin

35. Sierra snow pack Now and ………………….………….future?

36. Colorado River basin

37. Other impacts Increased wildfires Salinification of Sacramento Delta Extinction of Salmon in PNW? Cities vs. Farming

38. More wildfires 100% more acres burned in 2100

40. Less time for Salmon to reproduce Now: Lance Vail, PNNL Future:

41. Water use conflicts

42. Climate changes naturally San Diego (CA) Union Tribune; Phil Caterion

43. Conclusions Greenhouse induced climate changes will have a massive impact on the water resources of the western United States. The fabric of life in this region will be greatly altered by these changes….a “train wreck” in the making. What you have seen is a “best case” scenario (it could be worse and/or happen sooner).