Overview of terrestrial water storage changes over the Indus River Basin based on GRACE/GRACE-FO solutions

The Indus River Basin (the Indus) is facing the threat of great water shortages due to rapid population growth, expanding of irrigation area and increasing meltwater from snow and ice under the background of global warming. Being a less gauged basin, the effective usage of water resources in the Indus is always challenged by the high variability of the surface and ground water under a warming climate. This study therefore aimed to characterize and uncover the driving force of changes in water storage in the Indus based on GRACE and GRACE-FO solutions. A series of statistical techniques, such as EOF, modified STL, and Mann-Kenddall test, were applied to quantify and attribute the spatiotemporal patterns of the water storage dynamics. Our results demonstrated that (1) terrestrial water storage anomaly (TWSA) of the basin displayed a deficit and the deficit was largely concentrated in the middle and upper Indus plain (MUIP) during 2002 and 2020. (2) A slight decline in TWSA in the upper Indus basin (UIB) might be attributed to the accelerated melting of glacier and snow cover. (3) The excessive withdrawal of groundwater (1.57 mm/month) dominated the decrease of TWSA over the MUIP although weak increase of precipitation happened in the region. Anthropogenic activities imposed approximately 86.9% impact of the decrease in groundwater and this impact will aggravate for a long time if no effective water management schemes are taken. (4) Influenced by favorable meteorological conditions, the precipitation presented positive trend against the weakness of the India Summer Monsoon and the Westerlies, which exerted the positive influence on TWSA.