Evaluating Urban Heat Islands Dynamics and Environmental Criticality in a Growing City of a Tropical Country Using Remote-Sensing Indices: The Example of Matara City, Sri Lanka

Urbanization has undeniably improved human living conditions but has also significantly altered the natural landscape, leading to increased Urban Heat Island (UHI) effects. While many studies have examined these impacts in other countries, research on this topic in Sri Lanka remains limited. This study aimed to evaluate the effects of changes in built-up areas (BAs) and Vegetation Cover (VC) on UHI and environmental criticality (EC) in Matara cityCity, Sri Lanka, utilizing Landsat data. This study employed the commonly used remote-sensing (RS) indices such as the land surface temperature (LST), the UHI Index, and the Environmental Criticality Index (ECI). Various techniques were utilized including supervised image classification, Urban–Rural Gradient Zone (URGZ) analysis, grid-based analysis, UHI profiles, and regression analysis. The results revealed that built-up areas increased by 12.21 km2, while vegetation cover decreased by 9.94 km2, and this urban expansion led to a 2.7 °C rise in mean LST over 26 years. By 2023, newly developed BA showed the highest LST and environmental criticality, with mean LST values ranging from 25 °C to 21 °C in URGZs 1 to 15 near the city center, and lower values of 15 °C to 16 °C in URGZs 40 to 47 further from the core. The correlation analysis highlighted a strong positive relationship between the NDBI and LST, underscoring the significant impact of BA expansion on LST. Consequently, high-density built-up areas are experiencing high environmental criticality. To minimize these effects, planning agencies should prioritize green urban planning strategies, particularly in high LST and environmental criticality zones. This approach can also be applied to other cities to assess the UHI and LST phenomena, with the goal of protecting the natural environment and promoting the health of urban dwellers.