Retrogressive thaw slump expansion and vegetation phenological response in the Qilian Mountains, northeastern Tibetan Plateau

Permafrost degradation driven by climate warming is accelerating landscape changes in permafrost regions, with retrogressive thaw slumps (RTS) emerging as a critical disturbance. While many studies have focused on large‐scale RTS dynamics, the impacts of RTS on vegetation phenology at the watershed scale remain poorly understood. Here, we investigate the spatial heterogeneity of vegetation responses to RTS expansion in the Sala River Basin on the northeastern Tibetan Plateau. Our analysis reveals that the total RTS area increased nearly fivefold from 118, 719 m² in 2008 to 565, 432 m² in 2021, and that the distribution and expansion of RTS sites are strongly influenced by topographic factors such as elevation, slope, and aspect. The NDVI values within the basin decreased from northeast to southwest. There was an improvement in NDVI between 2017 and 2021. Although several sub-basins exhibited a downward trend in NDVI, the overall NDVI trends in RTS-affected areas indicate an increase in vegetation vigor over the study period. This suggests localized ecological resilience, possibly driven by enhanced groundwater recharge following permafrost thaw. This study advances our understanding of RTS impacts on alpine ecosystems by linking detailed RTS dynamics with watershed-scale vegetation responses.