Identifying the changes in terrestrial water storage is essential for a comprehensive understanding of the regional hydrological mass balance under global climate change. This study used a partial least square regression model to fill the observation gaps between GRACE and GRACE-FO and obtained a complete series of terrestrial water storage anomaly data from April 2002 to December 2020 from southeast China. We investigated the variations in terrestrial water storage anomalies in the region and the influencing factors. The study revealed that terrestrial water storage (TWS) anomalies have been increasing in the region, with an average increase of 0.33 cm/yr (p < 0.01). The intra-annual variation showed a positive anomaly from March to September and a negative anomaly in other months. Terrestrial water storage anomalies increased in most regions (especially in the central and northern parts), whereas they decreased in the southern parts. In terms of the components, the soil moisture storage (SMS) contributes 58.3 % and the surface water storage (SWS, especially reservoirs water storage) contributes 41.4 % to the TWS. The study also found that changes in the precipitation explain approximately 71.7 % of the terrestrial water storage variation, and reservoirs contributes to the remaining 28.3 %. These results are essential for understanding the changes in the hydrological cycle and developing strategies for water management in Southeast China.

The southeastern Tibetan Plateau (SETP), which hosts the most extensive marine glaciers on the Tibetan Plateau (TP), exhibits enhanced sensitivity to climatic fluctuations. Under global warming, persistent glacier mass depletion within the SETP poses a risk to water resource security and sustainability in adjacent nations and regions. This study deployed a high-precision ICESat-2 satellite altimetry technique to evaluate SETP glacier thickness changes from 2018 to 2022. Our results show that the average change rate in glacier thickness in the SETP is -0.91 +/- 0.18 m/yr, and the corresponding glacier mass change is -7.61 +/- 1.52 Gt/yr. In the SETP, the glacier mass loss obtained via ICESat-2 data is larger than the mass change in total land water storage observed by the Gravity Recovery and Climate Experiment follow-on satellite (GRACE-FO), -5.13 +/- 2.55 Gt/yr, which underscores the changes occurring in other land water components, including snow (-0.44 +/- 0.09 Gt/yr), lakes (-0.06 +/- 0.02 Gt/yr), soil moisture (1.88 +/- 1.83 Gt/yr), and groundwater (1.45 +/- 0.70 Gt/yr), with a closure error of -0.35 Gt/yr. This demonstrates that this dramatic glacier mass loss is the main reason for the decrease in total land water storage in the SETP. Generally, there are decreasing trends in solid water storage (glacier and snow) against stable or increasing trends in liquid water storage (lakes, soil moisture, and groundwater) in the SETP. This persistent decrease in solid water is linked to the enhanced melting induced by rising temperatures. Given the decreasing trend in summer precipitation, the surge in liquid water in the SETP should be principally ascribed to the increased melting of solid water.

The northeastern Tibetan Plateau (NETP), bordering the endorheic lake basins and the Upper Yellow River region, has been disturbed by increasing human activities in recent years. The NETP water storage changes could be a combined effect of climate variability/change and human activities (e.g., reservoir operation). However, whether the human activities have evidently altered hydrological processes and become key drivers of total terrestrial water storage (TWS) changes in the NETP remains unclear. To explore the roles of human interventions in changing surface water storage (SWS) and thus influencing regional TWS changes in the NETP, in comparison with natural drivers, this study quantitatively disaggregated and compared the contributions of TWS changes from climate-dominated natural lakes and man-regulated reservoirs at different timescales. Time series of Gravity Recovery and Climate Experiment (GRACE) TWS anomalies (TWSA) exhibited an overall upward trend (0.78 +/- 0.06 Gt/yr, p < 0.01) with evident periodic fluctuations from April 2002 to August 2020. Although the GRACE TWSA was more substantially influenced by changes in natural lake water storage (0.96 +/- 0.02 Gt/ yr) rather than reservoirs (0.54 +/- 0.04 Gt/yr) in the long-term trend, the man-regulated reservoir water storage changes can significantly dominate the GRACE TWSA on interannual and intra-annual timescales, especially in the second sub-period (2013.01-2017.06; GRACE TWSA change rate:-1.82 +/- 0.29 Gt/yr, p < 0.01, in comparison with the change rate of reservoir water storage of-1.28 +/- 0.17 Gt/yr, and the natural lakes of 0.72 +/- 0.07 Gt/yr). In some abnormal years, the reservoir storage changes were even close to the overall signal of region-wide GRACE TWSA. In addition, the increase in soil moisture storage (long-term linear trend: 0.65 +/- 0.06 Gt/yr, p < 0.01) was also a key factor that cannot be neglected. Our results suggest that human activities are becoming one of the key factors influencing TWS changes in the NETP.