Impact of urban morphology on microclimate and thermal comfort in northern China

This work is an experimental study focusing on the impact of urban morphology on the urban heat island (UHI) intensity, microclimate conditions and thermal comfort in a newly-developed urban area in Tianjin city, China. According to the Köppen-Geiger climate classification system, the studied area is classified as hot summer continental climate, characterized by hot and humid summers as well as cold and dry winters. Air temperature, relative humidity (RH) and wind speed at 46 points within an 8-km2 area are measured during both winter and summer seasons. Based on measured results and climatic mapping, the impacts of urban constituents such as building, pavement, greenery and water area on UHI intensity and microclimate conditions are analyzed. Results show that UHI intensity reaches up to 4.5 °C during daytime and 5.3 °C at night in summer, and 2.6 °C during daytime and 5.0 °C at night in winter. Thermal comfort level at the measurement points is predicted using the Thermal Sensation Vote (TSV) model developed for the local climate. The cooling effect of trees is evident during both daytime and nighttime in summer, but negligible in winter due to the reduction of leaf area and evaporation. The presence of both greenery and water body result in an increase in RH in air. Trees tend to reduce wind speed and improve thermal comfort in winter. Radiant heat dissipated from buildings and roads is the main contributor to nighttime UHI in both summer and winter seasons. Based on research results, urban design recommendations are proposed so as to improve outdoor thermal comfort in urban areas located in temperate climate zone during summer and winter.