Assessing the effects of climate change on the water resources of the Western United States

A regional assessment of the potential effects of climate change on the water resources of the western United States was performed by use of future scenarios for climate generated by global climate models incorporating CO₂concentrations at double current levels. The effect of these potential future climates was assessed with a spatially distributed water-balance model. Quantitative results were viewed not as predictions but as indications of the sensitivity of hydrologic resources and water institutions to potential change in climate. For two global climate models, effects of climate change on runoff vary across the western United States. Individual river basins change in annual runoff from +157 percent to -14 percent. Individual states show changes that range from +146 percent to -15 percent. Both models suggest that most river basins will experience an increase in peak flow and that snow-melt-dominated watersheds will shift to earlier peak flows. An amplification of the seasonal hydrologic cycle through increased peak flows and decreased low flows suggests new challenges for water managers and increased stress on aquatic ecosystems.