Application of distributed Xin'anjiang model of melting ice and snow in Bahe River basin

Study region: Bahe River basin on the Tibetan Plateau, China. Study focus: The thawing of glaciers and snow in cold regions is critical to the impact of runoff. This study proposes a distributed degree-day Xin'anjiang model (DD-XAJ) considering ice and snow thawing, which added the degree-day module describing snow and ice thawing to the previously distributed Xin'anjiang model. A sensitivity analysis of the main parameters of the improved model was conducted to discuss the effect of snow and glacier melt on the runoff process. The DD-XAJ model was also applied to the Bahe River basin to analyze its runoff change process and identify the composition of runoff components in the basin. New hydrological insights: The DD-XAJ model was successfully applied to the Bahe River basin, which is located on the Tibetan Plateau, with good daily runoff simulation results. The mean values of the Nash efficiency coefficients were 0.828 and 0.859 in the calibration and validation periods, respectively, and the mean values of the correlation coefficients were 0.917 and 0.941, respectively. The runoff composition of the Bahe River basin is mainly rainfall runoff (76.3 %), snowmelt runoff (16.7 %), and glacier melt runoff (7 %), which indicates that rainfall runoff plays a dominant role in the Bahe River basin. Snowmelt runoff is influenced by rainfall events, while glacier melt runoff is mainly influenced by the seasons. In addition, the contribution of runoff components in different elevation zones differed significantly. The contribution of elevation 4000-5500 m to the total runoff was the largest. This study provides a new understanding of runoff processes and runoff components in the cryosphere basin.