Urban Thermal Radiant Environment and Heat Stress

Abstract

Study intent This chapter discusses the impact of high-density urban form on the urban thermal environment from a human perspective: the heat stress. In contrast to the air temperature aspect that is normally investigated, the thermal radiant environment of urban settings is examined and the effective indicator of the mean radiant temperature (Tmrt) is used to characterize the urban thermal radiant environment and assess outdoor thermal comfort and heat stress. Two different urban settings with different building geometry and vegetation cover in downtown Shanghai were used as case study sites. A typical heat wave day in 2013 was selected to investigate the daytime radiant heat stress intensity. A GIS-based numerical simulation approach is used and the Solar and Longwave Environmental Irradiance Geometry (SOLWEIG) model was employed to investigate the spatial variation of Tmrt. Spatial analysis modules were developed and the Radiant Heat Stress Intensity index was defined. Result and discussion The study reveals that in Shanghai, under heat waves, the heat stress induced by the thermal radiant environment is quite severe, with Tmrt commonly well above 60 °C in daytime, and intra-urban Tmrt differences are largely influenced by building density and height, street orientation, and vegetation. Open paved spaces and space near sunlit walls are the places that have the highest Tmrt. In conclusion, the present study shows that the spatial variation of Tmrt can be used to identify thermally vulnerable areas and hotspots in complex urban environment and provide implications for urban design toward the mitigation of heat stress in high-density cities.