Glacial melting impact on runoff and evapotranspiration based on glacier-coupled SWAT model: A case study in the upper Shiyang River Basin, China

Glacial meltwater constitutes a vital component of the water supply in arid and semi-arid areas. However, the influence of glacial melting on runoff and evapotranspiration under global warming remains insufficiently understood. Previous studies coupling the Soil and Water Assessment Tool (SWAT) model with glacier modules often failed to consider the spatial heterogeneity of temperature during glacial melting, potentially leading to biased estimates of meltwater volume. In this study, we developed a glacier-coupled SWAT (SWAT-glacier) model considering the digital elevation model (DEM) based temperature-driven glacial melt processes to elucidate the impact of glacial melting on hydrological processes across four river basins (Dongda, Xiying, Jinta, and Zamu) of the upper Shiyang River Basin (SYRB) in northwestern China from 1986 to 2021. Compared with the standard SWAT model, the proposed SWAT-glacier model significantly improved the simulation accuracy for both runoff and evapotranspiration. Specifically, in comparison with the standard SWAT model, the Nash-Sutcliffe efficiency of the SWAT-glacier model showed a relative improvement of approximately 0.42%–9.16% and 1.50%–10.15% for runoff and evapotranspiration, respectively, in the four river basins during the validation period. Annual glacial runoff occurred predominantly from May to October, whereas glacial melt-induced evapotranspiration peaked between June and August. From 1986 to 2021, the average contributions of glacial melt to runoff were 6.97% for Dongda, 3.06% for Xiying, 2.70% for Jinta, and 0.67% for Zamu, whereas its contributions to evapotranspiration were 9.06%, 5.14%, 3.21%, and 1.59%, respectively. This study presents a SWAT-glacier modeling framework that enhances the simulation of hydrological processes in cold regions. The proposed methodology can be extended to other glacierized basins to provide valuable insights into water resource management under climate change.