Intra-urban differences of mean radiant temperature in different urban settings in Shanghai and implications for heat stress under heat waves: A GIS-based approach

The mean radiant temperature (Tmrt) is an effective indicator to characterize the urban thermal radiant environment and assess outdoor thermal comfort and heat stress. In this study, the SOLWEIG model (SOlar and Long Wave Environmental Irradiance Geometry) was employed to investigate the spatial variation of Tmrt in different urban settings in Shanghai. The model was tested against six directional radiant flux density measurements and showed good performance in Shanghai's urban environment. Two different urban settings with different building geometry and vegetation cover were used as case study sites. A typical heat wave day in 2013 was selected to investigate the daytime radiant heat stress intensity. Spatial analysis modules were developed and the Radiant Heat Stress Intensity index was defined. 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. The 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 towards the mitigation of heat stress in high-density cities.