Improvement of the Soil and Water Assessment Tool Model and Its Application in a Typical Glacial Runoff Watershed: A Case Study of the Qarqan River Basin, China

The composition of runoff in the basins located in the arid region of Northwest China is complex. How to better simulate and analyze the hydrological process and runoff situation of the basin through hydrological models is the key to the effective management of the regional water resources. This study focused on the Qarqan River Basin in Xinjiang, which is a typical river originating from glaciers and crucial for maintaining the oasis ecology in the downstream Tarim River. Based on the original SWAT model, a SWAT-Gla model containing a new glacier module was constructed according to the characteristics of the basin. After simulating, parameter calibration, and verification of the models, it was found that during the calibration period (1975–2009) and verification period (2010–2019), the R 2 , NSE , and PBIAS results of the SWAT-Gla model were much better than the original SWAT model. Moreover, SWAT-Gla could also simulate the runoff much better, especially in the peak and recession parts of the hydrograph compared with the original SWAT model. It was found that SWAT-Gla could better describe the runoff process in the basin where glacier recharge was the main component of runoff. Further, the analysis revealed that over the past 50 years, glacier and snowmelt water contributed to approximately 80% of the total basin recharge, which predominantly occurred from March to September. The volume of glacier meltwater exhibited a strong correlation with temperature, with both demonstrating an upward trend. The simulation found that in terms of groundwater, the groundwater recharge in the Qarqan River was relatively stable, stabilizing at 13% over the past 30 years, and groundwater recharge was mainly distributed in spring and summer, accounting for about 95% in total. Overall, we observed an increasing trend in the replenishment of glacial meltwater in both the surface runoff and groundwater in the basin. Therefore, it is essential to pay more attention to the future changes in water resources in the basin to ensure the sustainable development of water resources.