Assessment of natural and anthropogenic impacts on terrestrial water storage in the Loess Plateau based on different types of GRACE/GRACE-FO solutions

Changes in water resource storage are inevitable due to climate change and human activities, thus understanding alterations in water storage within a specific region is imperative for the planning and management of water resources. Data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are extensively employed to analyze large-scale total terrestrial water storage anomalies (TWSA). In this study, we derived a more reliable TWSA using different types of GRACE gravity models, which served as the basis for evaluating spatial and temporal variations in total terrestrial water storage and its hydrological components (soil moisture and groundwater) across the Loess Plateau. Additionally, we analyzed the impact of natural and anthropogenic influences on water storage in the Loess Plateau, categorizing them into primary and secondary influences, utilizing data on climate and human activities. The findings revealed a declining trend in the overall TWSA of the Loess Plateau, with a rate of decrease at - 0.65 +/- 0.05 cm/yr from 2003 to 2020 (P<0.01). As the direct factors affecting TWSA, soil moisture dominated the change of TWSA before 2009, and groundwater dominated the change of TWSA after 2009. Spatially, there was variability in the changes of TWSA in the Loess Plateau. More in-depth studies showed that soil moisture changes in the study area were primarily driven by evapotranspiration and temperature, with precipitation and vegetation cover status playing a secondary role. Human activities had a secondary effect on soil moisture in some sub-regions. Population change and agricultural development were major factors in altering groundwater storage in the study area. Other than that, groundwater was influenced by natural factors to a limited extent. These findings provided valuable insights for local governments to implement proactive water management policies.