On the evaluation of global terrestrial water storage and divergent governing factors centring policymaking

The GRACE satellite mission and its successor, GRACE Follow-On (GRACE-FO), have provided a paradigm shift in the near-continuous Earth mass observations since 2002. Despite adding a unique and unprecedented understanding of Terrestrial Water Storage (TWS)-one of 54 essential climate variables-at continental to global scales, its applicability is limited at the typical scale of interest to the regional water managers. Here, we compare GRACE(-FO) Mascon trends with Mean Field Trend (MFT) with improved spatial trends for the global land and Rodell key 34 regions. To further discern the applicability and robustness, five hotspot regions (ROIs) are selected, and the governing climatic and anthropogenic factors are analyzed, centering on groundwater-related policies and interventions, and further compared with in situ observations. The results show notable differences in MFT and Mascon trend values, particularly in regions with large ice masses. MFT overestimates positive trends (water gains) in 23 regions. It underestimates negative trends (water loss) in nine regions. Mascon trend range is within the MFT range in 30 regions, indicating the overestimation tendency by MFT. The climate influence primarily governed TWSA trends in ROI4 with a contribution of 73.4 % while the anthropogenic influence dominated the TWSA trends in ROI3 and ROI1 with 76.0 % and 64.0 % contributions. Compared with the extensive in-situ GW data, policy interventions and recharge interventions led to some cases of groundwater recovery in the ROIs, demonstrating the potential for sustainable aquifer systems.