Simulating Urban Heat Islands and Local Winds in the Dhaka Metropolitan Area, Bangladesh

Weather and climate changes due to urbanization are of great concern. This study examines urban effects on thermal and wind environments in the Dhaka metropolitan area, Bangladesh. For this, simulations for a case of hot days with weak synoptic forcing are performed using the Weather Research and Forecasting (WRF) model. The differences between the urban and no-urban simulations are analyzed in detail. In the urban simulation, the daytime sensible heat flux (latent heat flux) is considerably increased (reduced) and convective activities are enhanced. The nighttime urban heat island (UHI) is much stronger than the daytime UHI. In the daytime, the UHI effect on local winds is more important than the urban surface roughness effect. In the nighttime, the relative importance of the UHI and urban surface roughness effects differs depending on the region for given prevailing winds. Impacts of increases in anthropogenic heat and urban size are examined. As the anthropogenic heat increases, the UHI strengthens and the UHI effect on local winds is enhanced. As the urban size increases, the UHI and the UHI effect on local winds strengthen and the surface roughness effect appears in wider areas. This study provides further insights into urban effects on local winds.