Anticipated Impacts of Climate Change on U.S. Water Resources:
- Consistent with streamflow and precipitation observations, most of the continental United States experienced reductions in drought severity and duration over the 20th century. However, there is some indication of increased drought severity and duration in the western and southwestern United States (these apparent reverse trends result because increased evaporative demand associated with warmer temperatures more than balances precipitation increases).
- There is a trend toward reduced mountain snowpack and earlier spring snowmelt runoff peaks across much of the western United States. This trend is very likely attributable at least in part to long-term warming, although some part may have been played by decadal-scale variability, including a shift in the phase of the Pacific Decadal Oscillation in the late 1970s. Where earlier snowmelt peaks and reduced summer and fall low flows have already been detected, continuing shifts in this direction are very likely and may have substantial impacts on the performance of reservoir systems.
Source: U.S. Climate Change Science Program Synthesis and Assessment Product 4.3
- Stream temperatures are likely to increase as the climate warms, and are very likely to have both direct and indirect effects on aquatic ecosystems. Changes in temperature will be most evident during low flow periods, when they are of greatest concern. Stream temperature increases have already begun to be detected across some of the United States, although a comprehensive analysis similar to the one done for streamflow trends has yet to be conducted.
- A suite of climate simulations conducted for the Intergovernmental Panel on Climate Change’s Fourth Assessment Report shows that the United States may experience increased runoff in eastern regions, gradually transitioning to little change in the Missouri and lower Mississippi river basins, to substantial decreases in annual runoff in the Interior West (Colorado and the Great Basin).