Spatio-temporal dynamic land cover changes and their impacts on the urban thermal environment in the Chittagong metropolitan area, Bangladesh

The rapid urbanization and industrialization along with the expansion of cities in developing countries like Bangladesh converting vegetation and bare land into built-up area that remarkably boost up the land surface temperature (LST). This study has been conducted for correlating and monitoring the changes of landuse-landcover change (LULC) and LST of rapidly expanding Chittagong metropolitan area from 1989 to 2018 utilizing four Landsat satellite images (TM, ETM+, OLI, and TIRS). The Present study combines the techniques of remote sensing and geographic information system (GIS) to find out the spatial variation of LST and identify its relationship with LULC. Supervised classification technique has been employed in ERDAS IMAGINE 14.0 software to retrieve LULC data. The images of the study area were categorized into four different classes namely vegetation, urban structures, bared lands and water bodies. LSTs were estimated using the single thermal infrared band of Landsat TM, ETM+, and the band 10 and 11 of the TIRS sensor's image for the split-window algorithm method. Concerning the relationship between LULC and LST, it has been found that vegetation and water bodies shows lowest LST while bared lands and urban structures indicates highest LST. LULC analysis shows a dramatic increase in urban structures (from 20.83 to 58.93%), decrease in vegetation (from 56.54 to 20.24%) and bared lands (from 16.67 to 11.90%) and a further small increase in water bodies after the 80s, because of digging new ponds. LST in the study area has been increasing as high-temperature LU types have increased and low temperature LU types have decreased. Consequently, the mean annual temperature showed 6.5 degrees C increase, the minimum and maximum LST increased by 9 degrees C and 4 degrees C throughout the study period. The highest maximum and lowest minimum LST has found 40 degrees C during the years of 2010 to 2018 and 15 degrees C in the year of 1989, respectively. The study will assist the decision-maker to understand the impacts of unplanned urbanization for future city planning and urban management.

Automated summary

The study investigated the changes in LULC and LST in the rapidly expanding urban area of Bangladesh, finding that urban structures and bare lands have the highest LST, while vegetation and water bodies have the lowest. The research shows an increase in urban structures, a decrease in vegetation and bare lands, and a slight increase in water bodies. The increase in high-temperature LU types and decrease in low-temperature LU types led to a 6.5-degree Celsius increase in mean annual temperature.