Mitigating the urban heat island in a residential area in Tehran: Investigating the role of vegetation, materials, and orientation of buildings

Abstract

The results of researches on the urban heat island (UHI) effect and global warming have attracted more attention to the outdoor thermal comfort. This research evaluates the different strategies for daytime UHI mitigation due to thermal comfort conditions in Tehran which is affected by urban warming. The effects of urban vegetation (on the street level and on the roofs), high albedo surfaces (on the street pavements and on the roofs) and the orientation of buildings are analyzed through numerical simulations using the ENVI-met (version 4.3.0) microclimate model. In this study, an evaluation is carried out using various parameters including air (Ta) and surface temperatures (Ts), sky view factor (SVF), wind speed (WS), mean radiant temperature (MRT) and physiological equivalent temperature (PET). The results indicate that proper design of urban forms would largely mitigate UHI especially for new sustainable developments while thermal comfort improvements can be effectively achieved by increasing the urban vegetation coverage. Also the results demonstrate that there is no significant relationship between the UHI mitigation, and the improvement of thermal comfort. However, if lower surface temperatures are assumed as the basis for the UHI mitigation, a stronger correlation between UHI effect and thermal comfort can be observed.