Spatiotemporal Evolution, Co-Sensitivity Hotspots, and Robustness of Multi-Process Composite Ecological Sensitivity in an Alpine Mountain Region: A Case Study of Aba Prefecture, China

Alpine mountain regions are shaped by interacting ecological processes. Using Aba Prefecture on the eastern Qinghai–Tibet Plateau as a case study, we derived sensitivity indices for desertification, soil erosion, landslide disaster, freeze–thaw erosion, and habitat quality for six selected study years between 2000 and 2024, and integrated them into a composite ecological sensitivity index (CESI) using the spatial distance index. We assessed class transitions, trajectories, multiscale clustering, co-sensitivity hotspots, county-level and elevation-stratified patterns, and robustness. The results showed that: (1) mean CESI rose slightly from 1.483 to 1.487, indicating marginally weaker sensitivity, but fell to 1.427 in 2020; (2) 75.86% of the area retained its initial class, with persistent low, stable moderate, and persistent high trajectories covering 48.65%, 9.29%, and 15.37%, respectively, while spatial clustering weakened at coarser scales; (3) persistent co-sensitivity hotspots covered 2900.93 km2, the dominant 2024 combination was desertification–soil erosion–freeze–thaw erosion, and over 97% of highly and extremely sensitive areas and hotspots occurred above 4000 m, indicating a pronounced concentration of ecological sensitivity and co-sensitivity hotspots in high-elevation areas; and (4) continuous sensitivity gradients were robust, whereas class assignments and high-sensitivity boundaries were more responsive to factor composition, aggregation, and scale. The findings can inform spatial planning, the prioritization of environmental monitoring and field assessment, and differentiated ecological management in alpine mountain regions.