Evaluating dynamics of GRACE groundwater and its drought potential in Taihang Mountain Region, China

The Taihang Mountain Region (TMR) of China is an important headwater area that provides substantial water resources supporting the social and ecological stability of the North China Plain. Currently, groundwater resources in the TMR are rapidly declining, but the degree of groundwater storage (GWS) depletion and the driving mechanism of groundwater drought remain poorly understood. This study combined the Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) datasets to thoroughly analyze GWS changes in the TMR and the dominant driving factors during 2003-2016. In addition, a new index-the groundwater drought potential index (GDPI)-was established to quantify the potential of groundwater drought. We found that GRACE-derived terrestrial water storage in the TMR experienced a significant reduction (-21.82 mm/yr, p < 0.01) during 2003-2016, with a similar reduction in GWS (-21.22 mm/yr, p < 0.01). Human-induced impacts exerted a decisive role in GWS decreases in this region, with a relative contribution rate of 96% compared to the climatic contribution (4%). Climatic impacts on GWS were primarily observed in the southeastern TMR, where climate change appeared to be unbeneficial to groundwater recovery and exacerbated local groundwater depletion. Specifically, the groundwater drought potential was entirely increasing, indicating a worsened climate condition that precipitation increasingly failed to fill the groundwater deficit. Actions should be taken urgently to address the local groundwater crisis and to maintain water security. Our proposed GDPI not only reflected the degree of groundwater depletion but also revealed the relationship between groundwater drought and precipitation, making the index capable of being applied in drought forecasting. This study delivers a new perspective to better understand the mechanisms of GWS change and groundwater drought, and the results are expected to provide a valuable reference for groundwater management and water sustainability goals.