ASSESSING THE IMPACT OF ANTHROPOGENIC DROUGHT ON GROUNDWATER STORAGE IN THE COLORADO RIVER BASIN

The Southwest U.S. reportedly faces increasingly severe water shortages. The lack of water in reservoirs and rivers attracted much attention in media and scientific community, however, the impact on groundwater resources has been discussed less. A comprehensive monitoring and understanding of the dynamics of water resources is critical, and the investigation of innovative observation data not yet integrated in management practices may provide additional insights. This study investigates two decades of observations of the Gravity Recovery and Climate Experiment (GRACE) coupled with hydrological data to assess the impacts of anthropogenic droughts and climate change on groundwater resources within the Colorado River Basin (CRB). We estimate groundwater storage (GWS) variations across the basin and perform a thorough trend analysis. Our findings reveal substantial basin-wide declines of about 30.15 ± 28.81 km³ of GWS during the water years 2003 to 2023; and 18.91 ± 13.38 km³ of GWS during an intense recent drought from 2019 to 2022. Spatially separated analyses for CRB sub-basins reveal a steady depletion, without any recovery, of GWS in the Lower CRB since 2010. Despite temporary increases in snowpack levels in the Upper CRB, acceleration in GWS losses persists basin-wide, since 2019, underscoring the severity of water stress imposed on the region's over 40 million residents and agricultural sectors. Through comparisons with climate, surface water, snowpack, and groundwater well data, the observed storage dynamics are validated, providing crucial insights into the complex interplay of climate and anthropogenic factors driving water scarcity. Our research supports a regional and transboundary perspective on the water shortage in the CRB that considers both groundwater and surface water. The presented results underscore the urgent need for integrated strategies that promote resilience of water resources on and below the surface in the face of a changing climate.