Effectiveness and Tradeoffs between Portfolios of Adaptation Strategies Addressing Future Climate and Socioeconomic Uncertainties in California's Central Valley

The Central Valley of California is one of the major agricultural areas in the United States. The Central Valley Project (CVP) is operated by the Bureau of Reclamation to serve multiple purposes including generating approximately 4.3 million gigawatt hours of hydropower and providing, on average, 5 million acre-feet of water per year to irrigate approximately 3 million acres of land in the Sacramento, San Joaquin, and Tulare Lake basins, 600,000 acre-feet per year of water for urban users, and 800,000 acre-feet of annual supplies for environmental purposes. The development of effective adaptation and mitigation strategies requires assessing multiple risks including potential climate changes as well as uncertainties in future socioeconomic conditions. In this study, a scenario-based analytical approach was employed by combining three potential 21st century socioeconomic futures with six representative climate and sea level change projections developed using a transient hybrid delta ensemble method from an archive of 112 bias corrected spatially downscaled CMIP3 global climate model simulations to form 18 future socioeconomic-climate scenarios. To better simulate the effects of climate changes on agricultural water demands, analyses of historical agricultural meteorological station records were employed to develop estimates of future changes in solar radiation and atmospheric humidity from the GCM simulated temperature and precipitation. Projected changes in atmospheric carbon dioxide were computed directly by weighting SRES emissions scenarios included in each representative climate projection. These results were used as inputs to a calibrated crop water use, growth and yield model to simulate the effects of climate changes on the evapotranspiration and yields of major crops grown in the Central Valley. Existing hydrologic, reservoir operations, water quality, hydropower, greenhouse gas (GHG) emissions and both urban and agricultural economic models were integrated into a suite of decision support tools to assess the impacts of future socioeconomic-climate uncertainties on key performance metrics for the CVP, State Water Project and other Central Valley water management systems under current regulatory requirements. Four thematic portfolios consisting of regional and local adaptation strategies including changes in reservoir operations, increased water conservation, storage and conveyance were developed and simulated to evaluate their potential effectiveness in meeting delivery reliability, water quality, environmental, hydropower, GHG, urban and agricultural economic performance criteria. The results indicate that the portfolios exhibit a considerable range of effectiveness depending on the socioeconomic-climate scenario. For most criteria, the portfolios were more sensitive to climate projections than socioeconomic assumptions. However, the results demonstrate that important tradeoffs occur between portfolios depending on the performance criteria considered.