Evolution of water collection, storage, and supply functions and their coupling relationships in the Asian water tower from 2003 to 2023 based on GRACE and multi-source data

Study Region Tibetan Plateau (TP). Study Focus After data validation, this study constructed multi-product ensembles from multiple GRACE terrestrial water storage datasets and multi-source precipitation (P) and evapotranspiration (ET) products. From a functional perspective of the Asian Water Tower, net water input (N), terrestrial water storage change (TWSC), and runoff (R) were used to represent water collection, water storage, and water supply, respectively. Their interannual and seasonal variations and evolving pairwise coupling correlations were systematically analyzed. New Hydrological Insights for the Region During 2003–2023, the Asian Water Tower exhibited stable water collection (Sen’s slope = −0.065 mm yr −1 ), declining water storage (−0.171 mm yr −1 ), and enhanced water supply (0.211 mm yr −1 ). Spatially, water collection weakened in southern monsoon basins but increased slightly in eastern basins, while water storage declined consistently across most basins. Seasonally, the wet season contributed 98.1% of annual water collection and 94.7% of annual water supply, whereas the dry season experienced persistent storage loss (mean TWSC = −8.553 mm). Functional coupling showed pronounced seasonal differences: N–R coupling was strong in the wet season but decoupled in the dry season, indicating that dry-season runoff depended on antecedent water storage release rather than concurrent precipitation. Three change-point tests consistently identified significant shifts during 2008–2018, with the densest concentration around 2015; this transition was especially evident in 3- and 5-year windows.