Groundwater sustainability assessment in the Middle East using GRACE/GRACE-FO data

Remote-sensing hydrological data provided by the Gravity Recovery and Climate Experiment (GRACE/GRACE Follow-On) and reanalyzed ERA5-Land data allow for construction of a holistic picture of freshwater availability and successive wet/dry periods in the Middle East, a region with ground-data scarcity. The aim of this study is to conduct a comprehensive spatiotemporal and sustainability analysis of long-term (21 years, 2002-2022) GRACE-derived groundwater storage anomalies (GWSA) at 0.25(degrees) resolution over the Middle East. The time series of GWSA in each pixel is calculated after subtracting the soil-moisture anomaly, snow-water equivalent anomaly, and surface-water anomaly (all obtained from the ERA5-Land dataset) from the GRACE-based total water storage anomaly (TWSA) values. The Thiel-Sen slope method was used to detect the spatiotemporal patterns of GWSA over the region. An analytical groundwater sustainability index was developed based on three indicators-reliability, resiliency, and vulnerability-for the study area, on the basin scale. The statistical analyses revealed an average decline of -5.93 mm/year (-37.29 km(3)/year) for groundwater storage over the Middle East during the study period. The results suggest that most of the basins in the Middle East (59.14%) are operating extremely and severely unsustainably, while 34.41 and 6.45% of basins are slightly unsustainable and moderately sustainable, respectively. The results of this study uncover a holistic picture of groundwater variations and their sustainability over the Middle East, which can help to mitigate drought risks in the region, characterized by few publicly available ground-data sources.