Seasonal and diurnal surface urban heat islands in China: an investigation of driving factors with three-dimensional urban morphological parameters

Surface urban heat island (SUHI) can considerably influence the urban environment and the quality of life. It is vital to examine how underlying surface properties impact seasonal and diurnal SUHIs. However, the influence of three-dimensional (3D) urban morphological parameters (UMPs) on SUHIs has not been thoroughly studied under varying climatic settings. To fill this knowledge gap, the present study investigated seasonal and diurnal changes in SUHI intensities (Delta T) in 208 cities in China from 2014 to 2016 using moderate-resolution imaging spectroradiometer (MODIS) land surface temperature products. In addition, the influence of potential factors in urban surface energy balance, including two-dimensional (2D) and 3D UMPs, socio-economic indices, urban greening, and surface albedo, on seasonal and diurnal Delta T were assessed under different climatic settings and with different city sizes using the method of Geographically Weighted Regression (GWR). Results show that negative summer daytime Delta T was observed in some cities under dry climates. Generally, in summer, the Delta T during daytime was higher than at nighttime. The 3D UMPs (i.e. building height and volume) yielded more decisive influences on Delta T than 2D UMP (i.e. building coverage). This is particularly true for the summer diurnal cycle and under dry climatic settings. Building height was found to be negatively correlated with surface temperatures, while building volume was positively correlated. Additionally, the 3D UMPs yielded more influences on winter Delta T than summer Delta T. The capability of vegetation to regulate Delta T was more potent in dry climates than in wet climates and in small cities than in large cities. Varying climates and city sizes can modify the significance of the 2D and 3D UMPs on the urban surface energy balance, suggesting that urban thermal mitigation should consider climate background and population size.

Automated summary

Surface urban heat island (SUHI) has a significant impact on the urban environment and quality of life. This study found that three-dimensional urban morphological parameters (UMPs) have a more decisive influence on SUHI than two-dimensional parameters, especially in summer and under dry climatic conditions. Building height is negatively correlated with surface temperatures, while building volume is positively correlated. The ability of vegetation to regulate SUHI is more effective in dry climates and small cities. Varying climates and city sizes can modify the importance of two-dimensional and three-dimensional UMPs in the urban surface energy balance.