Scientists have developed a new method to help resource managers plan for possible changes in water supplies due to climate change, and have applied the technology to forecasting water supplies in California's Central Valley. Although it is not possible to provide exact forecasts of future climatic conditions, the new computer model projects that declines in precipitation, increases in temperatures, more frequent and longer droughts, and increased urban water demand, could result in significant reductions in streamflows. This would reduce the water available for animal and plant habitats, and for agricultural irrigation, and could result in a fundamental shift to dependence on groundwater. 

"Climate-change-induced aridity will prompt countless seemingly independent decisions in California's fields, factories, and homes to adjust sources of water supply that summed together can have a major impact on the state's environment, economy, and infrastructure," said USGS Director Marcia McNutt. "The value of this new model is that it provides far-sighted managers and alert stakeholders with a view to that future such that negative impacts can be anticipated and mitigated before they become problems." 

"This transition to using more groundwater may cause additional land subsidence that could be hazardous to agriculture, environmental habitat, and canal systems, as well as transportation and urban infrastructure, and could ultimately require water use limitations," said U.S. Geological Survey hydrologist and lead author, Randall Hanson. 

The Central Valley is one of the world's most productive agricultural regions, providing the U.S. with one quarter of the nation's food, including 40 percent of the nation's fruits, nuts, and other table foods. 

From 1961 to 2003, surface water supplied 53% of total water delivered to the Central Valley except during droughts. The Central Valley study demonstrates that the new method, coupling computer models of supply-and-demand-driven groundwater and surface-water systems, with global climate models, can show potential vulnerabilities in hydrologic systems and potential trends due to changes in climate. 

The unique model connects many environmental and human factors, such as water runoff from surrounding mountains, the demands, uses and movements of water for irrigation and natural vegetation, and the changes of groundwater and stream-flow supply under a climate change scenario. The model gives scientists and resource managers the ability to analyze the impacts of combined surface and groundwater use throughout the entire Central Valley hydrologic system.  

The USGS and the National Oceanic & Atmospheric Administration conducted the study using the existing Central Valley regional hydrologic model to develop the new tool. The tool could eventually be used as a blueprint for climate adaptation efforts for major aquifers across the United States and internationally, where there are complex agricultural, ecological and urban water demands. The article detailing this study, "A method for physically based model analysis of conjunctive use in response to potential climate changes," published in the journal Water Resources Research, and more information about USGS studies on climate change and water use can be found online.