Quantifying multi-sphere impacts on mountain runoff of a Third Pole River.

Abstract

Understanding the changes in mountain runoff and their driving forces across multiple spheres (e.g., atmosphere, glaciers, and vegetation) is crucial for water resource management in global mountain regions and their dependent downstream areas. However, the diverse impacts of these multi-sphere changes on mountain runoff remain inadequately quantified due to the lack of reliable datasets and methods. This study uses the upper Salween River (USR) basin as a case study, employs a high-resolution meteorological forcing dataset (TPMFD) to drive a physically based cryosphere-hydrology model (WEB-DHM-S), and quantifies the impacts of warming, wetting, glacier retreat, and vegetation greening on mountainous runoff through six sensitivity experiments. Sensitivity experiments revealed a slight but statistically insignificant downward trend (-1.5 mm yr^-1) in USR annual runoff from 1981 to 2020, with contributions from rainfall, snowmelt, glacier-melt, and baseflow being 57.5 %, 14.6 %, 5.3 %, and 22.7 %, respectively. Under a warming scenario, total runoff (TR) decreased by 37.5 mm, driven by substantial increase in evapotranspiration. Conversely, under a wetting scenario, annual TR increased by 10.5 mm. After the glaciers in high mountain areas had vanished, the intense precipitation and steep terrain of former glacial areas contributed to substantial runoff generation (+61.7 mm). Vegetation greening resulted in a TR decrease of 9.2 mm. Synergistic changes in glaciers‒vegetation and climate‒glaciers‒vegetation resulted in annual runoff decreases of 67.7 and 97.2 mm, respectively. Climate change (warming and wetting) played the dominant role in changing TR (73.3 %), while glaciers and vegetation played a regulatory role (26.7 %). These findings are significant for understanding the hydrological cycle and water resource management in the region, providing valuable insights for regional sustainable development strategies.