Impacts of two-dimensional and three-dimensional urban morphology on urban thermal environments in high-density cities: A case study of Hong Kong

Urban morphology has a major effect on urban thermal environments, particularly in high-density cities, which are prone to urban environmental problems such as urban heat islands and air pollution. Thus, this effect must be understood to enable the formulation of effective climatic planning strategies to mitigate thermal threats in such cities. In this study, multi-sourced thermal data, namely remotely sensed land-surface temperature (LST) data and mobilely collected air-temperature (AT) data, are used to comprehensively analyze the contribution of urban morphology to urban thermal environments in neighborhoods in Hong Kong. The most widely used urban morphology parameters, such as floor area ratio, building coverage ratio, sky view factor, mean building height, road density, and vegetation coverage ratio, are assessed. Analyses of LST data and AT data indicated that the morphology parameters controlling urban thermal environments during the daytime differed from those controlling urban thermal environments during the nighttime. Specifically, at the neighborhood level during the daytime, the thermal environment is controlled by two-dimensional morphology parameters, such as impervious surface area, whereas in the nighttime, it is controlled by both two-dimensional and three-dimensional morphology parameters, such as sky view factor and road density. Moreover, an investigation of the performance and scaling effect of key morphology parameters indicated that such attributes have diversely sized influencing areas. The findings of this study will facilitate the formulation of urban design strategies for effectively reducing thermal threats in cities, thereby supporting the healthy and sustainable development of high-density cities.