Seminar Sept 17th at 1 pm ET - Climate Extremes and Irrigation Water Source and Use Dominate Water Storage Changes Monitored by GRACE Satellites in Major U.S. Aquifers

There is considerable concern about water depletion caused by climate extremes (droughts and floods) and human water use in the U.S. and globally. Major U.S. aquifers provide an ideal laboratory to assess water storage changes from GRACE satellites because the aquifers are intensively monitored and modeled. In this Powell Center sponsored study we quantified total water and groundwater storage changes over 2002 – 2017 from GRACE satellites in 14 major U.S. aquifers and compared GRACE data with groundwater level monitoring and regional and global modeling results. 

The results were somewhat surprising, showing stable or rising long-term trends in the majority of aquifers with large scale depletion limited to agricultural areas in the semi-arid southwest and southcentral U.S. GRACE total water storage in the California Central Valley and Central/Southern High Plains aquifers, was depleted by drought and amplified by groundwater irrigation, totaling ~70 km3 (2002–2017), about 2× the capacity of Lake Mead. In the Pacific Northwest and Northern High Plains aquifers, lower drought intensities were partially dampened by conjunctive use of surface water and groundwater for irrigation and managed aquifer recharge, increasing water storage by up to 22 km3 over the 15 yr period. GRACE-derived total water storage changes in the remaining aquifers were stable or slightly rising throughout the rest of the U.S. Water storage changes were controlled primarily by climate extremes and amplified or dampened by human water use, primarily irrigation.

Intercomparing GRACE, traditional hydrologic monitoring, and modeling data underscores the importance of considering all data sources to constrain groundwater storage. GRACE satellite data have critical implications for many nationally important aquifers, highlighting the importance of conjunctively using surface-water and groundwater and managed aquifer recharge to enhance sustainable development.