Human-caused warming threatens to worsen Western droughts

The climate of the American West is likely to warm significantly over the next several decades, in significant part as a result of human-induced climate change.[[Climate Change Impacts Ã¢Â€Â¨on the United States
. (PDF) The Potential Consequences of Ã¢Â€Â¨Climate Variability and Change
 Foundation:  By the National Assessment Synthesis Team, US Global Change Research Program
 Published in 2001.]] That in turn is likely to lead to earlier snowmelt,[[Maurer, E.P., 2007, “Uncertainty in hydrologic impacts of climate change in the Sierra Nevada, California under two emissions scenarios”, (Abstract) Climatic Change, Vol. 82, No. 3-4, 309-325]] reduced streamflow in summer, more wildfires, increased mortality for fish, more beetle infestations and generally drier conditions in summer, even without any reduction in overall precipitation.

In addition, in some regions there will be less precipitation, compounding water scarcity. One paper in particular, published in Science, shows that climate models broadly agree that the American Southwest will receive less precipitation — and that this transition has in fact begun already. Droughts like the one that created the Dust Bowl of the 1930s will become common in the region.[[Vecchi, G., H. Huang, N. Harnik, A. Leetmaa, N. Lau, C. Li, J. Velez, et al. “Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America, 2007.” (Abstract) March 26, 2007.]]

Other scientists including Roger Pielke Sr., of the University of Colorado, argue that the growth of human population, with a corresponding growth in water demand will contribute even more to increased water scarcity than climate change will.[[Anderson, M. T., and L. H. Woosley. “Water Availability for the Western United States—Key Scientific Challenges.” (Abstract) U.S. Geological Survey Circular 1261, 85 p.]]