ASSESSING SUSTAINABILITY OF GROUNDWATER DEVELOPMENT USING GRACE SATELLITE DATA (Invited Presentation)

Understanding climate and human impacts on groundwater storage is critical for sustainable groundwater management. Here we evaluated climate and human drivers of total water storage (TWS) variability from GRACE satellites and compared the results with drought intensity and irrigation water use in 14 major aquifers in the U.S.. Results show that interannual variability dominates TWS time series tracked by GRACE satellites in most of the 14 major U.S. aquifers. Low trends in TWS in the humid eastern U.S. are related to low drought intensity. Although irrigation pumpage in the humid Mississippi Embayment aquifer is higher than that in the semi-arid California Central Valley, a surprising lack of depletion in TWS in the Mississippi Embayment aquifer is attributed to extensive streamflow capture. Large storage depletion in the semi-arid southwestern Central Valley and south-central High Plains totaled ~90 km³, about three times greater than the capacity of Lake Mead, the largest reservoir in the U.S.. Depletion in the Central Valley was driven by long-term droughts (up to 5 years) amplified by changing from mostly surface water irrigation to groundwater irrigation during drought. Low trends or slightly rising TWS trends in the northwestern (Columbia and Snake Basins) U.S. are attributed to dampening drought impacts by predominantly surface water irrigation. GRACE satellite data highlight synergies between climate and irrigation, resulting in little impact on TWS in the humid east, amplified TWS depletion in the semi-arid southwest and southcentral U.S., and dampened TWS deletion in the northwest and north central U.S.. Sustainable management of groundwater benefits from conjunctive use of surface water and groundwater with inefficient surface water irrigation increasing groundwater recharge and efficient groundwater irrigation reducing groundwater depletion. Managed aquifer recharge has also been increasing in recent years, particularly in the California Central Valley and in the northwestern U.S., with flood irrigation in the winter being used to recharge depleted aquifers. This study has important implications for sustainable groundwater development in many regions globally.