Spatio-temporal analysis of urban ecological degradation in a Himalayan municipality using remote sensing and their spatial association with infrastructure and transportation

Mountain cities are increasingly experiencing ecological stress due to rapid urban expansion, tourism infrastructure growth, and transportation development. In fragile Himalayan environments such as Darjeeling municipality, understanding the spatial dynamics of ecological quality is essential for sustainable urban planning. This study evaluates the spatio-temporal dynamics of ecological environmental quality in Darjeeling municipality using the remote sensing ecological index (RSEI) derived from multi-temporal Landsat 8/9 OLI/TIRS imagery during 2013–2024 to examine temporal variations with their temporal trend in key ecological indicators, and examine the spatial association between transportation corridors and ecological conditions. Four indicators i.e. NDVI, WET, NDBSI, and LST were integrated using principal component analysis to construct RSEI, followed by hotspot detection using the Getis–Ord Gi* statistic and temporal trend assessment using the Mann–Kendall test and Sen’s slope estimator. PC1 explained approximately 50–59% of total variance, confirming the comprehensiveness of the RSEI framework in representing ecological conditions. Spatial patterns reveal that good to very good ecological quality predominates in vegetated peripheral slopes, whereas moderate to poor conditions concentrate within the central urban corridor. The area under the Very Good ecological class peaked at 3.093 km2 in 2015 but declined to 1.380 km2 in 2018, indicating temporary ecological deterioration. Mean RSEI values ranged between 0.6285 and 0.7107, a weak and statistically non-significant trend (Sen’s slope = 0.000372, p = 0.837). Infrastructure proximity analysis shows that ecological quality generally improves with increasing distance from roads (r = 0.13–0.27), while areas within 0–30 m of infrastructure consistently exhibit lower RSEI values. These findings highlight the localized ecological impacts of transportation networks and urban expansion in mountain cities and provide a spatially explicit framework to support ecosystem-sensitive urban planning aligned with the United Nations Sustainable Development Goals.