[Change of vegetation ecological quality and the driving force in the Manas River Basin, China]

Ecosystems in inland river basins of arid regions are highly sensitive to climate change and human disturbance. Scientifically assessing the evolution of vegetation ecological quality and clarifying its driving mechanisms are crucial for regional ecological security and water resource management. We constructed a vegetation ecological quality index (VEQI) of Manas River Basin based on 250 m resolution remote sensing and meteorological data from 2000 to 2022. Using trend analysis, correlation analysis, and residual analysis, we examined the spatiotemporal variations of VEQI and quantitatively analyzed the driving effects and relative contributions of climate change and human activities. The results showed that vegetation in the Manas River Basin exhibited a significant improvement trend. During 2000-2022, the VEQI showed fluctuated increases with a rate of 0.4·a^-1. Improved areas accounted for 55.1% of the total area, primarily concentrated in the mid- and downstream oases, while degraded areas were sporadically distributed in urban expansion zones and high-mountain areas. The multiple correlation between VEQI and climatic factors was generally positive (R=0.3). Although rising temperature led to an increase in vapor pressure deficit and intensified atmospheric water stress, the increase in precipitation and artificial water resource regulation effectively compensated for such negative effect, facilitating a macroscopic trend of ecological improvement. Human activities played a dominant role in vegetation evolution with a contribution rate of 61.3%, while climate change contributed 38.7%. However, the driving mechanisms exhibited significant spatial differentiation. Human activities dominated vegetation evolution in the mid- and downstream oases (contribution rate >90%), while climate change mainly affected the southern mountains and northern deserts (contribution rate >70%). Our results indicated that the ecological improvement in the Manas River Basin was essentially a fragile improvement model, highly dependent on water resource regulation and human intervention. This study provides important implications for future water resource management and regional ecological security.