Quantifying the impact of vegetation changes on runoff in alpine basins using the Budyko framework integrating...

Vegetation is an indispensable component of the hydrological cycle, playing a critical role not only in modulating water balance but also in regulating ecohydrological processes within ecosystems. However, the specific contributions and mechanisms by which vegetation affects runoff dynamics in alpine catchments remain poorly understood. In this study, we developed a Budyko framework incorporating glacier effect at hydrological year and established a semi-empirical formula for estimating parameters (ω in the Budyko-Fu equation) based on the Normalized Difference Vegetation Index (NDVI) and climate seasonality. We employed the elasticity method to quantify the impact of vegetation changes on annual runoff in the Southwest Basin (SWB) of China from 2000 to 2020. The results show that the semi-empirical formulas used for annual-scale ω calculation demonstrated significant improvement in runoff estimation incorporating glacier effects. The Yarlung Zangbo River Basin (YZRB) shows the largest annual average improvement in ω (0.85%), followed by the Nu River Basin (NRB, 0.28%), while the Lancang River Basin (LRB) exhibits the smallest improvement (0.07%). Vegetation exerted a statistically significant positive impact on basin runoff (P < 0.001). On average, a 10% increase in NDVI corresponded to a 4.20% increase in runoff. Notably, this effect exhibited clear spatial heterogeneity across the nine sub-basins and generally intensified with increasing aridity. However, this trend may be slightly amplified by input data uncertainties in high mountain areas, and the results should be interpreted cautiously in data-scarce regions. These findings contribute to a more nuanced understanding of vegetation-runoff interactions at the interannual scale in alpine watersheds under global environmental change, providing critical insights for sustainable water resource management in glaciered regions.