Research on the relationship between urban morphology and air temperature based on mobile measurement: A case study in Wuhan, China

Urban morphology has an important impact on the outdoor thermal environment; studying the temporal and spatial distribution characteristics of air temperature and its relationship with urban morphology is the prerequisite for improving the outdoor thermal environment in the urban sectors. In July 2016, the study selected five sectors (C1 is a commercial sector, I1 is an industry sector, and R1-R3 are three residential sectors respectively) in the urban area of Wuhan to carry out the mobile measurement, and used ArcGIS tools to visualize the temporal and spatial distribution of air temperature, and then analyzed the correlation between air temperature and four indicators of urban morphology of the five sectors: building density(BD), vegetation coverage(VC), floor area ratio(FAR) and sky view fraction(SVF). The results suggested that: (1) In general, building density and floor area ratio are positively correlated with air temperature, while vegetation coverage and sky view fraction are negatively correlated with air temperature. (2) In the morning and evening hours, the maximum values of the average air temperature appear in the C1 (31.8 degrees C in the morning) and R1 (36.8 degrees C in the evening), which have the largest building density (56.4%) and the highest floor area ratio (4.87), respectively. While the lowest average temperature (27 degrees C in the morning, 31.5 degrees C in the evening) occurs in the R3 (a waterfront residential sector) with a large lake surface and the lowest building density. In the afternoon, the highest air temperature (41.5 degrees C) and the maximum temperature difference (4.2 degrees C) both appear in the R3 sector which has a complex urban morphology, with large area lakes, high density built-up areas and elevated road. (3) The water body has a significant cooling effect on the air temperature. In the R3 sector, the air temperature near the side of the water body is about 4.8 degrees C higher than the air temperature far from the side of the water body. (4) The relationship between floor area ratio, building density, sky view fraction and air temperature may not be a simple linear correlation, but there is a certain threshold. When they are greater than this threshold, the relationship between those indicators and air temperature will show an opposite trend. Since this phenomenon only occurs in some sectors, more data is needed to verify it.