Impact of urban canyon geometries on outdoor thermal comfort in central business districts

Due to the severe effect of urban heat island (UHI), the street geometries, including the orientation and aspect ratio, exert certain impacts on urban microclimates and outdoor thermal comfort. Designing sustainable cities requires a holistic approach. The objective of this study is to investigate how the canyon aspect ratio and orientation affect the street microclimate and outdoor thermal comfort in central business districts under the local climate of Nanjing city. To achieve this goal, a series of numerical simulations were conducted based on a total of 64 urban scenarios with various canyon aspect ratios and orientations. The microclimate simulation results for different urban models were used to predict the outdoor thermal comfort, which was evaluated with the physiological equivalent temperature (PET) index. The PET results indicate a certain correlation between canyon geometries and outdoor thermal comfort. Finally, several suggestions were proposed for urban planners and designers to implement mitigation strategies and methods to alleviate extreme heat stress, and toward the sustainable development of the contemporary cities.