Remote sensing based analysis of Urban Heat Islands (UHIs) with vegetation cover in Colombo city, Sri Lanka using Landsat ETM+ data

Urbanization leads to rapid constructions such as high rises, roads, pavements, parking lots, etc. Most of these constructions use materials with low albedo, such as asphalt, concretes and dark coatings which leads to high heat absorption in urban centers. In addition, removal of vegetation cover and emissions of waste heat by motor vehicles, air conditioners, power plants and factories contribute to the accumulation of heat energy, which leads to elevated temperatures in the urban centres forming Urban Heat Islands (UHIs). UHIs have many adverse socio-environmental impacts. Health problems, general discomfort, increased energy consumption for air conditioning, changing climatic patterns, air pollution, effects on water quality and aquatic eco systems are some of the notable effects of UHIs. Therefore, spatial identification of UHIs is a necessity to take appropriate remedial measures to minimize their adverse impacts. Satellite remote sensing is a cost-effective and timesaving method for spatio-temporal analyses of surface temperature distribution.

In this study, thermal bands (10.40 :m – 12.50 :m) of Landsat 7 ETM+ imagery acquired in 3 separate dates covering Colombo city of Sri Lanka are analysed for the spatio-temporal identification of UHIs. Distribution of vegetation cover in Colombo city is extracted by generating NDVI layers and analysed with the surface temperature distribution.

A deductive index is developed to identify the environmentally critical areas in Colombo city based on surface temperature distribution and vegetation cover. Remedial measures such as cool/green roofs, proper distribution of vegetation cover, increasing albedo of the city using light colour coatings, etc. can be introduced based on the results obtained here, in order to minimize the adverse effects of UHIs.