The effect of sky conditions and urban morphology on urban heat island in Seoul city

The urban heat island (UHI) is a serious climatological phenomenon that is likely to exacerbate the effects of climate change. It has adverse effects on the thermal comfort of urban dwellers, building energy consumption and the general health of vulnerable demographics (i.e. older people). To understand the effects of UHI and therefore devise efficient methods to mitigate it, it is important that we understand the many factors affecting UHI and the magnitude of their contribution on the manifestation of UHI, especially in urban areas. Consequently, in the current study, we study the effect of sky conditions and urban geometry on UHI in Seoul city, South Korea. The climatic data detailing diverse sky conditions, categorized by the amount of cloud cover, was collected from 28 Automatic Weather Stations (AWS) located in Seoul city. Information on urban geometry such as building density, gross floor area ration and building area ratio was obtained from satellite imagery. Our results indicate that the levels of UHI, quantified using urban heat island intensity (UHII), are dependent on the prevailing sky conditions. We found that, UHII was highest under cloudy sky conditions (r = 0.71) and lowest under clear sky conditions (r = 0.66). Furthermore, we found that UHII was correlated with building area ratio and gross area ratio; areas with high building area ratios and gross area ratios tended to also experience high UHII levels. The results presented in the current study are useful to policy makers or urban designers that wish to curb the increasing effects of UHI in urban areas and consequently improve thermal comfort in urban areas, reduce building energy consumption for space cooling purposes and prevent heat-related mortalities in old and vulnerable populations.