Estimating urban heat island intensity using remote sensing techniques in Dhaka City

Abstract

This study assessed the effects of urban heat island in Dhaka city, Bangladesh from 2002 to 2014 using remote sensing techniques. Land cover changes were characterized over a twelve year period with keen interested on urban expansion and the resulting impacts created by these changes on the land surface temperatures investigated. The study also compared the land surface temperature and ground station temperature data to validate the surface temperature in Dhaka. Maximum likelihood supervised classification method was used for the land cover classification resulting in a classification accuracy of 86.5% and 90.7% for 2002 and 2014 respectively. Remarkable change in land cover was observed in built-up areas which increased by 21% of the total land area from 74.12 to 135.36 square kilomentres in 2002 and 2014 respectively. Combined end member selection and linear mixture model techniques were used to estimate the surface emissivity of the land surface properties. The obtained surface emissivity together with the brightness temperatures of the thermal bands were then used to calculate the land surface temperature. Results showed that land surface temperature increased throughout the study area. Temperature ranges of 28.5°C to 35.4°C were observed in 2002 and 37.9°C to 40.1°C in 2014. The difference between ground-based temperature and the satellite derived temperatures for the ground weather station were +1.8°C and +2.7°C in 2002 and 2014 respectively. This margin of difference is attributed to sensor calibration errors. The land surface temperature increased across all land cover types over the twelve year period indicating existence and potential effects of urban heat highland in the Dhaka city. The results indicates that there is urgent need for the city authority to implement measures that must monitor and contain the resulting effects on the city population and infrastructure.