An improved SCF‑SWE relationship function with topographic controls for enhanced snowmelt runoff simulation

Study region The Yarlung Zangbo River Basin (YZRB), a representative high‑altitude alpine‑glacial basin in Xizang, southwestern China. Study focus To improve the snowmelt runoff simulation accuracy of the EasyDHM (Easy Distributed Hydrological Model) in the YZRB, this study proposes an improved snow cover fraction (SCF)-snow water equivalent (SWE) relationship function. Different from the baseline model adopting traditional empirical formulas, the new function incorporates the nonlinear Sigmoid-based physical mechanisms of snow evolution. By establishing a differential equation with SWE as the independent variable and integrating elevation and slope as dynamic constraints, the model better captures the spatial heterogeneity of snow distribution in complex alpine terrains. New hydrological insights for the region Multi-section validation demonstrates that the improved model significantly boosts runoff prediction accuracy, with the average Nash-Sutcliffe efficiency (NSE) increasing from 0.763 to 0.899 and the percent bias (PBIAS) dropping from 11.29% to 6.25% during the calibration period. The improved module effectively eliminates the premature runoff peaks in May, as found in the baseline model, ensuring precise phase alignment during the critical snowmelt period (March-June). Overall, the improved SCF-SWE relationship function enhances the model’s applicability, providing a reliable tool for snowmelt runoff simulation, water resource assessment, and hydrological forecasting in cryosphere-dominated basins.