1. Dennis P. Lettenmaier JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington April, 2003 A Brief History of Climate Change Sensitivity Work

2. Hydrology, water resources, and climate Hydrologists and water resources engineers have always had to deal with climate, it wasn’t just “discovered” But, the classical assumption is equivalent to statistical stationarity, “the future will resemble the past” Unfortunately, the future may not be like the past, which greatly complicates planning

3. Natural Flow at Lee Ferry, AZ Currently used 16.3 BCM allocated 20.3 BCM

4. Evolution of interest in climate change in hydrology ~1977 NAS/NRC report (various papers, basically said “we know how to deal with this”) Late 1980s AAAS study (Schaake paper evaluating water balance issues, SE U.S.) Late 1980s EPA Reports to Congress 1990s IPCC reports USNA (~40 papers cited on water resources and climate)

5. UW interest in hydrology, water resources, and climate change Hydrologic sensitivities of the Sacramento-San Joaquin River basin, California, to global warming (WRR, 1990) Climatic sensitivity of California water resources (JWRPM, 1991) Sensitivity of Pacific Northwest water resources to global warming (Northwest-Environmental-Journal, 1992) Water resources implications of global warming: A U.S. regional perspective (Climatic-Change, 1999) Effects of climate change on hydrology and water resources in the Columbia River basin (JAWRA, 1999)

7. Effects to Snowpack

8. Effects to Streamflow

11. More Storage Less Storage Number of Storage Failures optimization no optimization

12. U.S. Climate Change Study Basins (Lettenmaier et al. 1999)

13. VIC/ColSim 2040’s

14. Current Climate2040 Composite Scenario

15. So what is the issue for this meeting ? The fundamental implications of global warming for snowmelt dominated and transient snow rivers in the west have been well understood in the academic community for a decade or longer. Lots of questions about specifics, climate model uncertainty, etc. However, a) all models show there is a problem in snowmelt dominated watersheds, and b) the models are consistent with what’s been observed over the last half century or so. Almost all the studies are academic – few examples where the studies have been done by the water management agencies, using their own tools and models We are to the point where the question is no longer whether climate change is an issue, but rather how to incorporate it into the planning process (and preferably internalize it at the agency level)