Long-term changes in urban sprawl and its impact on surface urban heat island in a rapidly developing tropical coastal city, Kochi, India (2003–2020)

This study analyses seasonal and long-term variations in land surface temperature (LST), surface urban heat island (SUHI), and driving factors such as changes in land cover (LC) in the rapidly growing tropical coastal city, Kochi, India, from 2003 to 2020. This study integrates continuous gap-filled MODIS LST observations with LC changes, local climate zone (LCZ) analysis, and shifts in environmental drivers to evaluate long-term SUHI dynamics in the region. Rapid urbanisation resulted in the conversion of about 92 km 2 of vegetation cover to built-up area between 2002 and 2020, with built-up cover increasing from approximately 26% to62% in 2020, while vegetation declined from 62 to 28%. Both daytime and nighttime LST show a consistent increasing trend, with a higher warming rate from March to May. The increase in LST is significantly higher in densely built-up areas of the city, reaching up to ~ 2 °C/decade during the daytime and ~ 1.2 °C/decade at nighttime. SUHI intensity showed no significant long-term trend, with the mean daytime SUHI remaining around ~ 1 °C and exhibiting strong interannual variability. Increasing LST trends in both urban and suburban regions contributed to the absence of a significant long-term SUHI trend. Spatial analysis of land-use patterns reveals simultaneous core densification and outward expansion of built-up areas into peripheral zones of the city. These land surface transformations resulted in changes to the LCZ, with a significant area (~ 71%) of the city now covered by open low-rise buildings. The suburban regions, however, consist of a mix of low-density built-up classes, more vegetation and water bodies, leading to reduced LST. Seasonal variations in precipitation and vegetation further regulate surface temperatures, but the overall pattern is strongly driven by rapid urbanisation and the loss of vegetation. The results of this study can support climate-sensitive urban planning and policy making, understanding urban heat stress, minimizing health impacts, and developing sustainable, thermally resilient environments in rapidly developing cities.