Assessing urban heat island dynamics: A comparative study of Colombo district in 2015 and 2022

Abstract

Widespread industrialization and migration of the rural population to urban areas have led to rapid urbanization. This phenomenon transforms permeable surfaces into impermeable surfaces, leading to an increase in land surface temperature. This accelerates the formation of urban heat islands. Colombo city can be considered as the commercial capital of Sri Lanka. It is a densely populated and highly urbanized city. Over the past few years, residents have experienced discomfort due to elevated temperatures in the Colombo district. Hence, it is necessary to implement mitigation measures to reduce the impact of urban heat islands. Therefore, this study aims to identify urban heat islands in the Colombo district to facilitate the implementation of mitigation measures. To compare the urban heat island effect in Colombo district between 2015 and 2022, two Landsat 8 images with a cloud cover less than 10% were obtained from USGS Earth Explorer. Land surface temperature (LST) for both years was calculated using ArcGIS 10.8 software, utilizing bands 4, 5, and 10. Various equations were applied to determine Top of Atmosphere Radiance, Brightness Temperature, NDVI, Land Surface Emissivity, and finally LST. The LST data was then extracted for Colombo district, and another equation was used to generate a spatial distribution layer of urban heat islands for both years. When comparing the results obtained from the map of 2015 and 2022, an increase in the critically high urban heat island areas was observed, along with a relative decrease in the critically low urban heat islands. In conclusion, the comparative analysis of Urban Heat Islands (UHI) in the Colombo District for 2015 and 2022 shows significant temporal variations in thermal patterns. There is an increase in UHI intensity, which relates to the higher Land Surface Temperatures obtained according to the methodology, highlighting the dynamic nature of urban heat in rapidly developing regions. The spatial distribution of UHI effects proves considerable changes, with previously cooler areas showing intensified warming trends. The reasons for these could be land cover changes, such as increased impervious surfaces and reduced green spaces, playing a crucial role in UHI formation.