Extreme climate change and its impact on vegetation in the Qilian Mountains

In the context of global warming, increasing frequency of extreme weather events has become a major challenge for humanity, especially for climate-sensitive and ecologically fragile area. However, the patterns and underlying mechanisms of extreme climate events, and its effects on vegetation are even less explored in arid and semi-arid regions in northwest China. In this study, we systematically examined historical changes, driving mechanisms, future projections of extreme climate events, and their impacts on vegetation dynamics in the Qilian Mountains, which is a key ecological security barrier in northwest China. We found that both extreme temperature and precipitation events in the Qilian Mountains have increased significantly in intensity, frequency, and duration over the past six decades, with pronounced spatial heterogeneity. Extreme low temperatures increased faster than extreme high temperatures, leading to a reduced diurnal temperature range, while heavy precipitation and wet-day precipitation contributed increasingly to annual totals. These changes are closely associated with intensified Eurasian anticyclonic circulation, enhanced geopotential heights, and increased moisture transport, modulated by phase shifts in the AMO, PDO, and AO. Future projections show continued intensification of extreme warming and precipitation, accompanied by a decline in cold and freezing days, especially under high-emission scenarios. From 1982 to 2015, NDVI in the Qilian Mountains exhibited an overall increasing trend, with 3.34% of the area showing a significant decreasing trend and 38.11% showing a significant increasing trend. Grasslands dominated the areas where vegetation significantly increased. Precipitation emerged as the main climatic factor limiting vegetation growth in the region, with the extreme precipitation intensity index contributing the most to NDVI, accounting for 17.1%. Both climate change and human activities jointly influenced vegetation dynamics, with differing dominant drivers between greening and browning areas. These findings improve understanding of climate–vegetation interactions in arid mountain systems and provide scientific support for ecosystem management and climate adaptation strategies in the Qilian Mountains.