The Ecological Quality Variation of Vegetation on the Tibetan Plateau from 2001 to 2020 and Its Relationship with Westerly Monsoon Synergy

This study evaluates the spatio-temporal variations in vegetation ecological quality (EQI) on the Tibetan Plateau (TP) from 2001 to 2020 by integrating net primary productivity (NPP) and fractional vegetation cover (FVC). The results show that annual EQI increased at 0.8 decade−1, with 65.6% of areas exhibiting improvement, particularly in sparse grasslands and mixed forests. NPP and FVC rose by 5.4 g C m−2 decade−1 and 0.008 decade−1, respectively, displaying southeast–northwest spatial gradients. Climate warming (0.18 °C decade−1) and wetting (27.5 mm decade−1) drove EQI trends, with temperature positively correlating with EQI in eastern forests (29% mixed forests) but negatively in southern grasslands. Atmospheric circulation further modulated EQI: enhanced zonal water vapor flux and monsoon indices (IVarea, EMI) significantly impacted 10–25% of areas. Despite persistent improvement trends (13.9% of TP), 5.9% of regions face sustained degradation risks, emphasizing the need for climate-adaptive vegetation management. This synthesis of ecological-climate coupling provides actionable insights for conservation on the warming TP.