Asymmetric impact of vegetation change on runoff and evapotranspiration in the Yellow River source region

The Yellow River Source Region (YRSR) Vegetation dynamics play a critical role in regulating hydrological processes in cold alpine watersheds; however, quantitatively disentangling their impacts on runoff and evapotranspiration remains challenging and uncertain. Focusing on the YRSR, this study developed an enhanced hydrothermal coupling model within the Budyko framework to quantify the sensitivity and relative contributions of vegetation change to runoff and evapotranspiration, with particular emphasis on their asymmetric responses to vegetation dynamics. During 1981–2020, vegetation cover and evapotranspiration in the YRSR exhibited significant increasing trends, and runoff showed a slight but statistically insignificant decline. This contrasting pattern is projected to persist under continued climate warming and ecological restoration. Vegetation greening promoted evapotranspiration while suppressing runoff, and its influence on runoff (17.17 % of the total variation) was stronger than that on evapotranspiration (11.31 %), indicating a clear asymmetric hydrological response to vegetation change. In comparison, permafrost degradation contributed 27.98 % to runoff changes and 41.59 % to evapotranspiration variations, suggesting that runoff variability is predominantly controlled by climate change (54.85 %), whereas evapotranspiration dynamics are more strongly regulated by vegetation and permafrost changes. These findings demonstrate the synergies and trade-offs between vegetation dynamics and water resources in the YRSR and provide region-specific insights for supporting adaptive water resource management under ongoing warming and vegetation greening on the Qinghai–Tibet Plateau. • Vegetation dynamics in YRSR have asymmetric impact on runoff and evapotranspiration. • Vegetation and permafrost drive asymmetric hydrological responses in YRSR. • Mean NDVI is a suitable indicator for vegetation-induced hydrological effects. • Permafrost degradation modulate vegetation–hydrology interactions and asymmetry.