Integrating Comprehensive Ecological Indicators to Develop a Novel Dryland Ecological Risk Index for Ecological Risk Assessment in Arid Watersheds

Ecological risk assessment in arid inland river basins is challenging because ecological degradation is jointly controlled by water scarcity, surface exposure, thermal stress, energy exchange, and vegetation buffering. Existing remote sensing indices primarily characterize ecological quality and provide limited representation of risk formation and transmission. This study developed a Dryland Ecological Risk Index (DERI) within the source–pathway–sink framework to assess ecological risks in the Shiyang River Basin from 2000 to 2025. The Bare Soil Index and Temperature Vegetation Dryness Index represented risk sources, land surface temperature and albedo characterized transmission pathways, and the Normalized Difference Vegetation Index and wetness index represented ecological sinks. Principal component analysis, correlation analysis, high-resolution imagery, and comparison with the Remote Sensing Ecological Index were used for model validation, while transition matrices characterized changes among risk classes. The first principal component explained 93.97–97.51% of the total variance, and the directions of indicator loadings were ecologically consistent. DERI was most strongly correlated with drought stress (TVDI, r = 0.58) and effectively identified fine-scale degradation in deserts, bare land, oasis margins, and oasis–desert transition zones. Ecological risk exhibited a pronounced south–north gradient, with lower risks in the Qilian Mountains, oases, and river corridors and higher risks in the northern deserts. Basin-wide risk intensified during 2000–2010, underwent substantial spatial restructuring during 2010–2015, and gradually declined after 2015. The proportion of class V areas decreased from 32.94% in 2000 to 15.35% in 2025; nevertheless, classes IV–V still accounted for 52.40% of the basin in 2025. These findings demonstrate that DERI provides a process-oriented and spatially sensitive tool for identifying ecological risk hotspots and supporting differentiated ecological management in water-limited watersheds.