Assessing terrestrial water storage variations in Afghanistan using GRACE and FLDAS-Central Asia data

Study region: Afghanistan, Central Asia. Study focus: In this study, we evaluated the terrestrial water storage dynamics in Afghanistan and its five major river basins using the terrestrial water storage anomalies (TWSA) from three Gravity Recovery and Climate Experiment (GRACE) mascons observations from JPL, CSR, and GSFC processing centers, and the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System - Central Asia (FLDAS-CA) simulation. New hydrological insights for the regions: Since 2008, due to intense and prolonged drought conditions and groundwater overexploitation, TWS in Afghanistan has been decreasing at an alarming rate. The average slopes of the TWSA trend in Afghanistan for the GRACE period (2003-2016) of the three products range between - 3.6 to - 4.8 mm/year. The decrease in TWS is further exacerbated during the GRACE-FO period (2019-2022), ranging between - 20.4 to 30 mm/year. Because groundwater is heavily relied on in the country but human-induced change (i.e., groundwater extraction) is not simulated in FLDAS-CA, a significant difference could be observed between GRACE observations and FLDAS-CA results, especially following after each severe drought event (e.g., 2008, 2018) when substantial groundwater extraction occurred. The assimilation of GRACE observations into the FLDAS-CA framework will undoubtedly have a positive impact for decision-makers and local stakeholders in preparing and mitigating the impacts of drought and groundwater overexploitation in Afghanistan and Central Asia.