Quantifying the impact of snowfall and snow cover on runoff in the Tibetan plateau using a modified Budyko framework

Climate warming has reduced snowfall and snow cover on the Tibetan Plateau (TP), but quantitative assessments of their coupled impacts on runoff remain limited. This study develops a novel Budyko framework that couples Snowfall Ratio (SR) and snow cover Fraction (FSC) to quantify their previously unquantified antagonistic effects on runoff in the Tibetan Plateau. The key innovations are: (1) Physical process coupling explicitly incorporates evaporation limitation on snowfall and energy prioritization for snowmelt. (2) Spatially divergent responses reveal significant SR declines in Southern/Central basins (max -7.22 mm yr^-1, ∗p∗<0.01) versus increases in Northeastern basins (+2.59 mm yr^-1), contributing to a basin-wide SR reduction of 17.0%. (3)The model demonstrates superior performance, achieving Nash-Sutcliffe efficiency (NSE) values 0.70∼0.87, compared to 0.22∼0.53 for the traditional Budyko, alongside a 68∼82% reduction in error. (4) Antagonistic effects demonstrate that reduced SR reduced runoff by 17∼44% through enhanced snowpack retention, while decreased FSC increased runoff by 4∼10% via accelerated melt. Collectively, these processes accounted for 21∼54% of runoff variability-which are systematically underestimated by conventional models. This mechanistic framework significantly improves runoff prediction in snow-dominated basins, supporting water security assessments for Asia's water towers under climate change.