An Analysis of Drought Resislience of the California Central Valley Surface-Groundwater-Conveyance System Norman L. Miller 1* , Larry L. Dale 2 , Charles F. Brush 3 , Sebastian D. Vicuna 1*4 , Tariq N. Kadir 3 , Emin C. Dogrul 3 , and Francis I. Chung 3 1) Geography Department, University of California, Berkeley and Climate Science Department, Berkeley National Laboratory, CA, USA, nlmiller@berkeley.edu 2) Energy Efficiency Department, Berkeley National Laboratory, Berkeley, CA, USA 3) Modeling Branch, California Department of Water Resources, Sacramento, CA, USA 4) Civil and Environmental Engineering Department, University of California, Berkeley, CA, USA ABSTRACT A series of drought simulations were performed for the California Central Valley using computer applications developed by the California Department of Water Resources and historical datasets representing droughts from mild to severe for periods lasting up to 60 years. Land use, cropping patterns, and water demand were fixed at 2003 levels and water supply was decreased by 25 and 50 percent, representing light to severe droughts. Impacts were examined for four sub-basins, the Sacramento Basin, the San Joaquin Basin, the Tulare Basin, and the Eastside Drainage. Results suggest the greatest impacts are in the San Joaquin and Tulare Basins, heavily irrigated regions with overdraft most years. Regional surface water diversions decrease by as much as 70 percent. Most significant was the decline in groundwater head for the severe drought cases, where results suggest that under these scenarios the water table is unlikely to recover within the model-simulations. However, the overall response to such droughts is not as severe as anticipated and the Sacramento Basin may act as groundwater insurance to sustain California during extended dry periods. This approach, coupled with remote sensed observations, is being evaluated as a technology transfer to other nations. Key words: Drought simulation, surface-groundwater response, pumping, technology transfer. INTRODUCTION The western United States has experienced periods of long drought conditions since the last glacial epoch 11,000 years ago. The period between 900 and 1400 A.D. was a time when severe long-duration droughts occurred in the western U.S. (Cook et al. 2004). This Medieval mega-drought period was followed by a less severe drought period that was coincident with the Little Ice Age cooling period. Samples from sediments, tree rings, and tree stumps, combined with isotope dating analysis have been used to reconstruct these naturally occurring droughts that lasted 50 to more than 100 years (Stine 1994; Herweijer et al. 2006; Cook et al. 2007). More recently, four droughts in the western U.S.