Abstract
Urban heat island effects, which are the phenomenon wherein higher ambient air temperatures are measured in cities than in rural areas, have worsened urban thermal environments over the past decades. This study aims to analyze the effects of urban physical environments on the duration of high air temperature, using climate data collected from 217 Automatic Weather Stations in Seoul, Korea. In order to specify radiation trapping effects, interaction effects between sky view factors (SVF) and albedo values were analyzed using multiple regression analysis. The results indicate that increases in commercial and traffic areas lead to longer durations of high air temperature and that high urban porosity shortens the duration of high air temperature by improving urban ventilation. This study also indicates that the duration of high air temperature has a negative association with SVF; however, an analysis of interaction effects indicates that high-albedo materials diminish the positive effects of high SVF largely because of radiation trapping effects. These findings suggest that urban ventilation paths, high SVF, and materials with an appropriate albedo value play important roles in improving thermal comfort conditions, such as the duration of high air temperature.
Highlights
The results of the bivariate regression analysis indicated that higher sky view factors (SVF) values shortened the durations of high air temperature in both albedo groups, as shown in Table 3; based on the difference in regression coefficients, it was found that the positive effects of the SVF on the dependent variable were relatively diminished in the high albedo group compared to the low albedo group (Figure 7)
This analysis, represents the fact that, even if an urban area is built with an optimal design plan in consideration of Urban Heat Island (UHI) effects, the mitigation effects of the SVF can dwindle in an urban canyon with high-albedo materials, due to solar radiation trapping effects
The present study used a multiple regression model to examine the impacts of urban physical environments on the durations of high air temperature during the summer season
Summary
With the current climate change and global warming trends, average air temperatures are rising worldwide; this phenomenon has had a critical impact on thermal environments in densely built-up urban areas with impervious surfaces, causing Urban Heat Island (UHI) effects. Two increasing public demands in Seoul, Republic of Korea, are to mitigate UHI effects and to ameliorate thermal comfort in outdoor areas. UHI effects have become a threat to urban populations in the Seoul area as well; the Seoul Metropolitan Government has devised and adopted various UHI mitigation strategies. The augmentation of vegetated areas and open water surfaces, the application of cool paving materials, and the creation of urban wind corridors for ventilation have been suggested as possible mitigation strategies to lower air temperatures in the city
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