RSEI-Based Assessment of Ecological Quality in an Alpine Transitional Region Incorporating Climate Accumulation Effects and Multiscale Drivers

The ecological security of the Qinghai–Tibet Plateau (QTP) alpine transitional region plays a critical role in regional and global climate regulation. Conventional Remote Sensing Ecological Index (RSEI) assessments, however, rely on single-date imagery and often fail to account for cumulative climatic effects. To address this limitation, we refined the traditional RSEI through a multi-principal component weighting scheme that retains over 95% of the cumulative variance. Using imagery from five discrete periods between 2000 and 2020, we evaluated the spatiotemporal evolution of regional ecological quality in the alpine transitional region in Gannan. Results show an overall improvement: mean RSEI increased from 0.63 to 0.69, Good/Excellent areas expanded from 65.6% to 79.9%, and the interquartile range decreased from 0.19 to 0.14. Spatially, ~59% of the area improved, whereas ~41% degraded, primarily in western transition zones and urban peripheries. As an evaluation of internal index contributions, NDVI remained the dominant structural component. Climatic constraints shifted from temperature dominance between 2005 and 2010 to precipitation dominance by 2020, with all interactions exhibiting synergistic enhancement. Cumulative climatic variables during the growing season, with an optimal seven month accumulation window, substantially outperformed single month variables in explaining ecological variations. Specifically, mean q-values increased by 0.12 for temperature and 0.18 for precipitation, yielding a 15 to 25 percent relative improvement, which validates the necessity of incorporating cumulative effects. This framework provides a robust foundation for long-term monitoring and differentiated management of fragile alpine ecosystems.