Contrasting determinants of land surface temperature in three megacities: Implications to cool tropical metropolitan regions

Megacities in tropical regions are among the urban centers most vulnerable to increasingly intense heatwaves. However, the complex interactions between urban characteristics and thermal environments are yet to be fully understood. Here, we investigated the relationship between urban characteristics and land surface temperature (LST) for three megacities in the tropical savannah climate zone, Chennai, Dhaka, and Kolkata. LST values were retrieved from Landsat 8 data, and urban features were constructed using digital surface models, building footprints, and satellite imagery. Model-agnostic approaches were adopted to analyze the impacts of urban characteristics on LST. The boosted regression tree (BRT) model was used to capture the nonlinear effects of six most important factors on LST changes. The dominant influencing factors of LST were normalized difference built-up index, albedo, and normalized difference vegetation index. Building roofs, roads, and other hardscapes with high-albedo materials are preferred in alleviating surface urban heat island effect in Dhaka and Kolkata. The placement of urban parks with woody vegetation in an area larger than 0.6 ha produced effective cooling effect. In Chennai and Kolkata, urban policies to increase sky view factor are recommended. The application of BRT model with integrated urban data provides unique insights for thermal resilience planning.

Automated summary

The complex interactions between urban characteristics and thermal environments in megacities in tropical regions are yet to be fully understood. This study investigated the relationship between urban characteristics and land surface temperature (LST) in Chennai, Dhaka, and Kolkata. The study found that factors such as normalized difference built-up index, albedo, and normalized difference vegetation index were most influential in determining LST. The study recommended using high-albedo materials for building roofs, roads, and hardscapes to alleviate surface urban heat island effect in Dhaka and Kolkata, and increasing sky view factor in Chennai and Kolkata.