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° 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 km³/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.