Examining urban heat island progression in Chennai: temporal insights from 2014 to 2024

The Urban Heat Island phenomenon has emerged as a significant environmental challenge, particularly in rapidly urbanising cities. Chennai, a coastal metropolis in southern India, has undergone extensive urban expansion over the past decade, resulting in significant changes in land use and land cover (LULC) and temperature fluctuations. This study examines the spatiotemporal progression of the Surface Urban Heat Island (SUHI) in Chennai over a decadal period (2014-2024), incorporating an intermediate assessment for 2019 to capture transitional dynamics capturing relative thermal variability rather than absolute temperature trends. A GIS and remote sensing-based methodology was employed, integrating multi-source satellite datasets. Landsat 8 OLI/TIRS was used consistently to derive Land Surface Temperature (LST), Normalised Difference Vegetation Index (NDVI) and Normalised Difference Built-up Index (NDBI), ensuring temporal comparability, while Sentinel-2 A data were utilised for high-resolution LULC classification. SUHII was computed using a standardised formulation to minimise background climatic influence and enable inter-temporal comparison. The results reveal a significant increase in built-up areas from 36% in 2014 to 67% in 2024, accompanied by a decline in vegetation cover from 25% in 2014 to 10% in 2024. Temporal analysis indicates an increasing trend in NDBI and a decreasing trend in NDVI, reflecting intensified urbanisation. A strong positive correlation between NDBI and SUHI intensity was observed, whereas NDVI exhibited a weaker negative correlation, suggesting that existing green spaces may be insufficient or spatially fragmented for effective heat mitigation. These findings provide a refined understanding of urban heat dynamics by distinguishing relative thermal anomalies from absolute trends, emphasising the need for spatially targeted, climate-responsive urban planning strategies.