Remote sensing based analysis of urban heat islands with vegetation cover in Colombo city, Sri Lanka using Landsat-7 ETM+ data

• Urban heat islands (UHIs) in Colombo city were identified using satellite remote sensing.
• Green spaces in Colombo city was extracted using NDVI method.
• Correlations of heat islands and green spaces were evaluated.
• Environmentally critical areas were identified w.r.t. heat islands and vegetation.
• Recommendations were given to increase the environmental quality of critical areas.

Urbanisation leads to rapid constructions, which use low albedo materials leading to high heat absorption in urban centres. In addition, removal of vegetation cover and emissions of waste heat from various sources contribute to the accumulation of heat energy, leading to formation of urban heat islands (UHIs). UHIs have many adverse socio-environmental impacts. Therefore, spatial identification of UHIs is a necessity to take appropriate remedial measures to minimise their adverse impacts. Satellite remote sensing provides a cost-effective and time-saving methodology for spatio-temporal analyses of land surface temperature (LST) distribution.In this study, thermal bands (10.40–12.50 μm) of Landsat-7 ETM+ imagery acquired in 3 distinct dates covering Colombo city of Sri Lanka were analysed for the spatio-temporal identification of UHIs. Vegetation cover of Colombo city was extracted by using NDVI method and subsequently examined with the distribution of LST.A deductive index was defined to identify the environmentally critical areas in Colombo city based on the distribution of LST and availability of vegetation cover. Accordingly, Colombo harbour and surrounding areas were identified as the most critical areas. Remedial measures can be taken in future urban planning endeavours based on the results of this study.