PNNL

Abstract

Global warming will impact the hydrologic cycle by increasing the capacity of the atmosphere to hold moisture. Anticipated impacts are generally increased evaporation at low latitudes and increased precipitation at middle and high latitudes. The impacts on specific regions will depend on changes in weather patterns and are certain to be complex. Here we apply a suite of 12 potential climate change scenarios that could occur over the next century as atmospheric CO2 concentrations reach double the pre-industrial level to the Hydrologic Unit Model of the United States (HUMUS) to simulate water supply in the conterminous United States. In Part 4 we examine the sufficiency of this water supply to meet changing demands of irrigated agriculture. General Circulation Models (GCMs) used to simulate climate disagree on whether the US as a whole and its constituent regions will receive more or less precipitation as global warming occurs. The changes in water yield driven by changes in climate will likely be most consequential in the semi-arid western parts of the country where water yield is currently scarce and the resource is intensively managed. Changes of greater than +/-50% with respect to present day water yield are projected in parts of the Midwest and Southwest US. Interannual variability is likely to increase with reduced water yield but decrease with wetter conditions.