Detecting the changing impact of urbanisation on urban heat islands in a tropical megacity using local climate zones

• Natural areas are 2.4°C and 1.3°C cooler than compact and open areas, respectively. • Open low-rise, mid-rise and high-rise built areas are most suitable for Dhaka. • No statistical LST differences between compact and large low-rise built areas. • NDVI properties of compact and heavy industry are statistically identical. This study integrates urban morphology-based heat island estimates with Local Climate Zone (LCZ) classifications, a methodology that is relatively underexplored in the context of tropical megacities. We use Land Surface Temperature (LST), and Normalised Difference Vegetation Index (NDVI) measured from satellite data to establish the differences across the LCZ classes and to identify suitable climate-sensitive built-environments for the megacities. High-density built-up areas had higher LSTs and Surface Urban Heat Island (SUHI) estimates than areas with more vegetation. When comparing average summer LSTs in built-up areas, areas with higher building density and minimal vegetation cover were 1.2 ° C warmer than the more open built environments. Natural areas, on the other hand, showed an average LST that was 2.4 ° C cooler than the compact built environment and 1.3 ° C cooler than the open built environment. For tropical megacity Dhaka, open low-rise, mid-rise and high-rise morphology emerges as more favourable built environment benefiting both people and the local biodiversity. Conversely, areas comprising compact mid-rise, large low-rise and heavy industry buildings that are becoming increasingly densely populated, are the least suitable options. Given the increasing need for high-density living, our results indicate that the most suitable approach to planning would be to substitute compact low-rise housing, typically prevalent in developing country megacities as slums, with a combination of open high-rise and open mid-rise housing. This study demonstrates that increasing SUHI and LSTs can be mitigated in densely populated tropical megacities by appropriate planning using urban morphology as demonstrated by LCZ classification.