Response of grassland NDVI change velocity to climate velocity in the alpine mountainous region

Under climate warming, grassland vegetation in mountainous regions responds rapidly to climate change but often lags behind the rate of climatic shifts. The Qilian Mountains (QLMs), a representative alpine mountainous area, have experienced a warming rate significantly exceeding the global average. However, whether the change velocity of grassland NDVI in the QLMs matches climate velocity remains unclear, and there is an urgent need to determine if regional grasslands can adapt to the “velocity race” driven by climate change. To address this gap, this study analyzed the spatiotemporal trends of change velocities in growing-season grassland NDVI (NDVI_GS), temperature, and precipitation across the QLMs using the local climate velocity method combined with a moving window technique. Results showed that from 2000 to 2024, the velocities of grassland NDVI_GS, temperature, and precipitation all increased, with precipitation velocity exhibiting the fastest growth rate. Their mean values were 0.08 ± 0.08 km·a⁻¹ (NDVI_GS), 0.07 ± 0.07 km·a⁻¹ (temperature), and 0.24 ± 0.26 km·a⁻¹ (precipitation), indicating that grassland NDVI_GS velocity was intermediate between temperature and precipitation velocities. Spatially, 54.1 % of grassland areas displayed NDVI_GS velocities exceeding temperature velocities, while 77.8 % of areas showed NDVI_GS velocities lower than precipitation velocities. In conclusion, the response of grassland NDVI_GS velocity to temperature and precipitation velocities exhibits regional heterogeneity. These findings provide important scientific insights for guiding grassland restoration and adaptive management in alpine mountainous regions.