The climatological literature contains considerable evidence that increasing concentrations of atmospheric carbon dioxide will result in global warming. In order to investigate the effects of resultant climatic changes on runoff in the Great Basin, a water balance model based on average monthly precipitation and temperature was applied to four watersheds in the region. The most probable change, a 2°C increase in temperature coupled with a 10% reduction in precipitation, results in decreases in runoff ranging from 17% to 38% of the present mean, with drier basins showing the greater change. Increasing the precipitation deficit to 25% yields runoff reductions of 38% up to 51%. Equivalent changes to a cooler, wetter climate show corresponding increases in runoff of approximately the same magnitude, but such a shift is not considered likely in the area. Reduced water supply under the moderately warm, dry scenario was compared to projected year 2000 water demand. Many regions of the Great Basin would experience severe water shortages were this change to occur. Even in those areas where supply would still exceed consumptive demand, instream flow requirements would be dangerously threatened.hydrology collectio
