Assessing long-term vegetation dynamics and urban expansion in an industrial city of Eastern India using Landsat time-series and Google Earth Engine

Abstract

Rapid urbanisation and industrial expansion of eastern Indian cities like Durgapur raise concerns about vegetation degradation, surface-water decline and built-up expansion. This study examined three decades of environmental change in Durgapur (1995–2025) using harmonised Landsat 5, 7, 8, and 9 Collection 2 Level-2 surface reflectance imagery processed in the Google Earth Engine JavaScript Code Editor. The annual cloud-masked median composites were subjected to analysis using NDVI, NDWI, NDBI, the Mann–Kendall trend test, Sen's slope estimator and correlation analysis. The NDVI value averaged for the city was 0.35 in 1995, which declined to a minimum of 0.25 in 2009 before reclaiming 0.44 in 2024. It is observed that the NDWI value remained consistently negative (−0.27 to −0.41), whereas the NDBI value increased steadily from −0.01 to −0.05, which distinguishes progressive urbanisation. The trend analysis revealed that vegetation greenness showed a significant positive monotonic increase (Kendall's τ = 0.26; p = 0.025; Sen's slope = 0.003 NDVI units yr⁻¹; 95% CI: 0.0005 – 0.0050). NDVI was found to be negatively correlated with NDWI and NDBI, and NDWI was positively correlated with NDBI (p<0.001). Further, spatial analysis showed positive vegetation changes in the peri-urban agricultural fringe (τ > 0.30) and continuing decline in the central industrial core (τ < −0.30). The findings demonstrate concurrent long-term changes in vegetation, surface moisture, and built-up characteristics and provide spatially explicit evidence to support sustainable urban planning, green infrastructure development, and environmental management in rapidly industrialising cities.