CLIMATE WARMING AND WATER MANAGEMENT ADAPTATION FOR CALIFORNIA STACY K. TANAKA, TINGJU ZHU, JAY R. LUND, RICHARD E. HOWITT, MARION W. JENKINS, MANUEL A. PULIDO, M ´ ELANIE TAUBER, RANDALL S. RITZEMA and IN ˆ ES C. FERREIRA Department of Civil and Environmental Engineering, Department of Agricultural and Resource Economics, University of California, Davis 95616 E-mail: jrlund@ucdavis.edu Abstract. The ability of California’s water supply system to adapt to long-term climatic and demo- graphic changes is examined. Two climate warming and a historical climate scenario are examined with population and land use estimates for the year 2100 using a statewide economic-engineering op- timization model of water supply management. Methodologically, the results of this analysis indicate that for long-term climate change studies of complex systems, there is considerable value in including other major changes expected during a long-term time-frame (such as population changes), allowing the system to adapt to changes in conditions (a common feature of human societies), and representing the system in sufficient hydrologic and operational detail and breadth to allow significant adaptation. While the policy results of this study are preliminary, they point to a considerable engineering and economic ability of complex, diverse, and inter-tied systems to adapt to significant changes in climate and population. More specifically, California’s water supply system appears physically capable of adapting to significant changes in climate and population, albeit at a significant cost. Such adapta- tion would entail large changes in the operation of California’s large groundwater storage capacity, significant transfers of water among water users, and some adoption of new technologies. 1. Introduction In Hades, the mythical Tantalus was burdened by a great thirst, only to have the water rise to his neck threatening to drown him, but then recede when he tried to drink. At the same time, ever present above him was a large rock, ready to crush his head at some uncertain time. Like Tantalus, California’s water managers are tantalized by the prospects of quenching California’s thirsts, but constantly contend with floods and droughts, while living in a world of such grave prospects as earthquakes, energy and budget crises, population growth, and climatic change. In California, concern for climate change has increased in recent years with research on global climate change applied to California and studies of how California’s climate has changed recently (Dettinger and Cayan, 1995; Gleick and Chalecki, 1999; NRC, 1999) and in recent millennia (Stine, 1994, 1996; Haston and Michaelson, 1997; Meko et al., 2001). Several decades of studies have shown that California’s climate is variable over history and in the present (Cayan et al., 1999), is experiencing continuing sea level rise, and may experience significant climate warming (Gleick, 1987; Roos, 1987; Lettenmaier and Gan, 1990; Snyder Climatic Change (2006) DOI: 10.1007/s10584-006-9079-5 c  Springer 2006