Abstract
Many studies have found that larger parks might be needed to counteract the Urban Heat Island effects typical in densely populated Asian megacities. However, it is not easy to establish large parks to serve as urban cool islands in Asian megacities, where little space exists for large urban neighborhood parks. Officials in these cities would rather use small areas by replacing heat-absorbing artificial land cover with natural cover. The main objective of this study was to understand the cooling effect of changes in land cover on surface and air temperatures in urban micro-scale environments for supporting sustainable green-space planning and policy in densely built-up areas. This was achieved using measurements at different heights (ground surface, 0.1 m, and 1.5 m) for five land cover types (LCTs) and modeling with the micro-scale climate model ENVI-met. At all vertical measuring points, the average temperature over the entire measurement period had the same hot-to-cold order: asphalt > soil > grass > water > forest. However, the value dramatically decreased as the measuring points became higher. The intensity of hot and cool spots showed the highest value at surface by 18.2 °C, and declined with the height, showing 4.1 °C at 0.1 m and 3.1 °C at 1.5 m. The modeling results indicated that the well-known diurnal variation in surface insolation also occurred in our small domain, among the various LCTs. Based on these findings, providing small-scale green infrastructure in densely built-up areas could be an effective way to improve urban micro-scale thermal conditions.
Highlights
The urban heat-island effect is a phenomenon that occurs when the air temperature over urban areas is significantly higher than that over surrounding rural areas due to increased amounts of anthropogenic heat, heat-absorbing land cover, air pollution, and the reduction of green spaces as urban areas develop
The urban cool island (UCI) effect is the phenomenon that occurs when lower air temperature occurs in green spaces, than occurs in artificial surroundings
Since UCIs can mitigate negative urban heat-island effects, many studies have been performed to identify cooling effects of green spaces that might serve as tools to ameliorate the effects of climate change [6,7,8,9,10]
Summary
The urban heat-island effect is a phenomenon that occurs when the air temperature over urban areas is significantly higher than that over surrounding rural areas due to increased amounts of anthropogenic heat, heat-absorbing land cover, air pollution, and the reduction of green spaces as urban areas develop. Higher temperature has impacts on the habitability of cities. It could increase the risk of mortality [1,2,3,4], and could increase the consumption of energy for cooling in summer, thereby contributing to global warming [5]. The urban cool island (UCI) effect is the phenomenon that occurs when lower air temperature occurs in green spaces, than occurs in artificial surroundings. Since UCIs can mitigate negative urban heat-island effects, many studies have been performed to identify cooling effects of green spaces that might serve as tools to ameliorate the effects of climate change [6,7,8,9,10]. Larger parks might be needed to counteract the UHI effects that typically cause such suffering in densely populated cities, such as Asian megacities
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