Regulation of runoff by snow and glacier meltwater in the Yarkant River Basin, Tarim Basin

Runoff in the Upper Yarkant River Basin is strongly influenced by glacier and snow meltwater, yet their long-term contributions and regulatory effects remain insufficiently quantified. The SPHY model was therefore applied to simulate and partition runoff during 1962—2022 using CN05.1 daily meteorological data, MODIS snow-cover fraction data, glacier inventory data, and observed runoff records from the Kaqun hydrological station. The results showed that annual runoff depth increased significantly at a rate of 9.2 mm per decade. This increase was mainly driven by significant increases in glacier-melt runoff and rainfall runoff, at rates of 4.9 and 4.2 mm per decade, respectively, whereas snowmelt runoff exhibited no significant trend. On average, glacier-melt, snowmelt, rainfall runoff, and baseflow contributed 62.2%, 18.5%, 13.3%, and 6.0% of total runoff, respectively. The relative contributions of these runoff components remained largely stable across different hydrological year types. Sensitivity experiments revealed that increases in air temperature of 1 ℃ and 2 ℃ would increase annual runoff depth by 19.9% and 42.6%, respectively, while precipitation increases of 10% and 20% would enhance runoff by 5.7% and 12.0%. In contrast, reductions in glacier area of 5%, 10%, and 20% would decrease annual runoff depth by 11.7%, 18.3%, and 28.4%, respectively. Overall, runoff in the Upper Yarkant River Basin was persistently controlled by glacier-melt, although the rainfall runoff contributions have increased in recent decades. Continued glacier retreat is expected to weaken meltwater supply and reduce the basin’s runoff-regulation capacity during the ablation season. These findings provide a scientific basis for assessing future changes in glacier and snow meltwater and for developing adaptive water-resources management strategies in the Upper Yarkant River Basin.