Climate Change Impacts on Extreme Wet and Dry Events for Southern California Water Resources

English Abstract:

Southern California’s lack of local water supplies has caused the region to extensively rely on imported sources originating from snowpack in the Sierra Nevada and Rocky mountains. This study evaluates how climate change will impact the interannual variability of runoff primarily generated from snowpack across all imported supplies of water to Southern California including 1) the Sacramento River basin, 2) the San-Joaquin River basin, 2) the Tulare Lake basin, 3) Mono Lake and Owens Valley basin and 4) the Colorado River basin. A 10-member ensemble of coupled global climate models are dynamically downscaled forcing one regional and one hydrological model resulting in a high-resolution 4.6-km output for the region. Greenhouse gas concentrations are prescribed according to the IPCC Representative Concentration Pathway 8.5 using the present-day period of 1966-2005 and future period of 2011-2050. Projected changes in average annual runoff across all basins are minimal. However, the likelihood of experiencing above or below average annual runoff increases. Supplies of water are further constrained under extreme dry conditions. Yet extreme wet years do not necessarily equate to an increase in water supply availability as the majority of precipitation occurs in the winter months and water must be released for flood control purposes. Significant water management problems can arise as the region currently does not possess enough surface water storage facilities to capture rising quantities of runoff.