IMPACTS 
Water
Water shortages—already a problem for California—will likely get much worse if global warming continues unchecked, with consequences for city-dwellers, agriculture, and taxpayers. The chief reason is that much of the state's water supply during the dry spring and summer months comes from snowpack in the Sierra Nevada mountains, which could virtually disappear by the end of the century due to global warming. Meanwhile, demand for water is expected to increase—both because of the hotter climate and population growth.
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Shrinking Snowpack
By the end of the century, if global warming emissions continue unabated, statewide annual average temperatures are expected to rise into the higher warming range (8 to 10.5°F). This temperature rise will lead to more precipitation falling as rain instead of snow, and the snow that does fall will melt earlier, thus decreasing the spring snowpack in the Sierra Nevada by as much as 90 percent. This would pose extreme challenges to water managers, hamper hydropower generation, and nearly eliminate skiing and other snow-related recreational activities. However, if global warming emissions are significantly curbed and temperature increases are kept in the lower warming range, the losses in snowpack are expected to be only half as great.
Costly Challenges
As global warming continues, decreasing snowmelt and spring stream flows, coupled with increasing demand for water resulting from a growing population and a hotter climate, will likely lead to more water shortages. By the end of the century, if temperature increase reaches the medium warming range (5.5 to 8°F) and precipitation decreases, spring streamflow could decline up to 30 percent. Agricultural areas are expected to be hard hit, with southern California farmers able to access about 25 percent less water than they need. As a result of increasing temperature and population, residential ratepayers and agricultural water customers are also expected to pay more than $600 million more per year for water toward the end of the century than they otherwise would have paid due to normal cost increases.
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Sources
Cayan, D.,A. Luers, M. Hanemann, G. Franco, and B. Croes. 2006. Climate change scenarios for California: An overview. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications
/CEC-500-2005-186/CEC-500-2005-186-SF.pdf.
Hayhoe, K., D. Cayan, C.B. Field, P.C. Frumhoff, E.P. Maurer, S.C. Moser, S.H. Schneider, K.N. Cahill, E.E. Cleland, L.L. Dale, R. Drapek, W.M. Hanemann, L.S. Kalkstein, J. Lenihan, C.K. Lunch, R.P. Neilson, S.C. Sheridan, and J.H. Verville. 2004. Emissions pathways, climate change, and impacts on California. Proceedings of the National Academy of Sciences 101:12422-12427.
Medellin, J., J. Harou, M. Olivares, J. Lund, R. Howitt, S. Tanaka, M. Jenkins, and T. Zhu, 2006. Climate warming and water supply management in California. Draft report. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications
/CEC-500-2005-195/CEC-500-2005-195-SD.pdf.
