Abstract

Changing climate conditions have been identified as a major threat to the sustainability and availability of water resources in the Southwestern U.S. Long-term decreases in precipitation can lead to reductions in regional groundwater levels and loss of groundwater storage in aquifers for some communities. Reduced precipitation can also lead to lower water levels in streams and losses in the vegetation that grows alongside riverbanks.

The goal of this project was to identify how hydrologic systems in the Southwest might respond to changes in climate and the degree to which this response is dependent on the characteristics of the hydrologic system. To do this, researchers developed a tool that simulates how quickly water moves from the surface to underground aquifers.  The tool helps identify timeframes and regions where seepage of water into aquifers is likely constant, rather than fluctuating with rainfall patterns or climate. By locating these areas upfront, researchers can exclude them from their analysis and focus water supply forecasting efforts on areas where groundwater is more likely to be affected by changes in rainfall or human uses at the surface.

The model shows that areas with a shallower water table tend to have more variability in the rate at which groundwater supplies are replenished, with secondary effects related to the soil type and the period of variation. In these areas, changes in rainfall and water withdrawal for irrigation or urban use have a bigger impact on groundwater availability. Water resource managers can use this tool to more accurately forecast how much groundwater remains in different watersheds and to determine which systems will be most sensitive to changes in climate and water use. The need for better forecasting is only increasing, as aquifers are increasingly tapped and precipitation patterns are expected to become more variable.