Variability of long-term terrestrial water storage changes and its environmental effects in the Three Rivers Source Region, China

Climate change and anthropogenic activities have driven significant terrestrial water storage changes (TWSC) in the Three Rivers Source Region (TRSR), exerting profound impacts on freshwater availability across China and broader Asia. However, long-term TWSC characterization remains challenging due to limited observational data in this alpine region. Here, we integrate GRACE observations (2002-2020), ERA5-Land reanalysis, and GLDAS data to reconstruct TWSC using two methods: (1) the water balance method (PER) and (2) the component summation method (SS), applied to three input datasets (ERA5-Land, GLDAS, and their average, GL-ER). Comparative analysis reveals that the SS method applied to GL-ER yields the highest consistency with GRACE-derived TWSC. Using this optimal approach, we extend the analysis to 1951~2020, uncovering spatiotemporal TWSC patterns. Although annual TWSC trends appear negligible due to strong seasonality, we introduce the intra-year TWSC fluctuation (TWSCF) index to quantify cumulative variability. A significant (p < 0.05) transition occurred in 1980, with TWSCF shifting from a declining trend (-0.39 mm/yr) to an increasing trend (0.56 mm/yr), primarily driven by soil moisture changes. However, Hurst exponent analysis suggests this upward trend may not persist. Drought and vegetation assessments indicate concurrent wetting and greening in the TRSR. TWSC correlates strongly with meteorological drought, acting as a reliable drought indicator while its linkage with vegetation dynamics suggests a potential contribution to greening. Our findings provide a robust framework for understanding long-term TWSC evolution and its hydrological-ecological interactions under climate change.