Ecosystems and human activities associated with these areas are particularly vulnerable to extended droughts and may be affected significantly by ecological changes resulting from long-term climate change. Municipal use is of growing but of secondary importance. Vulnerability to climate is mediated by the rivers, surface reservoirs, and groundwater aquifers that supply most of the water for the region. But many aquifers are being mined and are only partly replenished by precipitation. Hot, dry conditions bring on rapid evapotranspiration from crops and surface supplies.
Irrigated agriculture is by far the largest user of water in the Southwest.
Presently, water supplies in the Southwest are about 50 percent surface water and 50 percent groundwater. More groundwater is being pumped than replenished in most regions. Municipal water use is increasing with rapidly growing populations and economic development. Rights to their water have been fully allocated between nations, states, and different water users. Understanding variations and potential changes in the flows of these rivers is critical for water resources, energy and ecosystem management in our region.