Canopy-scale Built-environment Characteristics and Urban Heat Island Effect in a Tropical Medium-sized City

Jou-Man Huang,Yu-Su Wang,Liang-Chun Chen,Heui-Yung Chang

doi:10.3390/su13020868

Jou-Man Huang, Yu-Su Wang + Show 2 more

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https://doi.org/10.3390/su13020868

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Abstract

Previous studies have found that built-environment characteristics in large cities produce important effects of the urban heat island (UHI) and know the horizontal space affected by the urban canopy microclimate ranges from about 30–200 m, but there are few studies in medium-sized cities. Therefore, this study investigates canopy-scale built-environment characteristics and their correlation with urban heat island (UHI) effects in Chiayi city, a tropical, medium-sized city. Under a 100 m buffer size, 2D and 3D built-environment factors such as the green coverage ratio (GCR), building coverage ratio (BCR), floor area ratio (FAR), and sky view factor (SVF) were first analyzed and then correlated with the UHI effect. The analyses were repeated on 200 and 1000 m scales and compared to previous studies. It was found that the built-environment factors were more strongly correlated with UHI under the 200 m buffer. Moreover, 2D factors such as the GCR and BCR had a higher correlation with UHI, especially in developing medium-sized cities. Regarding the GCR, BCR, and FAR, as expected, the correlation coefficients with UHI increased to 0.4 at 13:00 during the day and changed from 0.2 to 0.4 at 00:30 at night, whereas the correlation between the SVF and UHI was greatly different from the study area or calculation methods. The scale effect and SVF calculation methods are recommended for further study.

Highlights

Since the Industrial Revolution, the rapid transition from agricultural land to urban land has resulted in artificial material increasingly covering the land surface, and the subsequent engineering construction, human activities, and energy consumption have led to changes in the urban climate [1,2,3]
These findings indicate that the urban heat island (UHI) effect in medium-sized cities may be as notable as that in megacities
These results suggest that the 2D built-environment factors such as the green coverage ratio (GCR) and building coverage ratio (BCR) likely impact the UHI of a medium-size city as greatly as that of a megacity

Summary

Introduction

Since the Industrial Revolution, the rapid transition from agricultural land to urban land has resulted in artificial material increasingly covering the land surface, and the subsequent engineering construction, human activities, and energy consumption have led to changes in the urban climate [1,2,3]. According to United Nations 2018 statistics, 55% of the world’s population is concentrated in urban areas. This ratio is expected to increase to 68% by 2050 and approximate 90% in high-income countries such as those in. The UCL is defined as the layer of space extending from the ground to building roofs, namely, the microscale climate phenomenon. It is the most affected by human activities and is closely related to the construction density, building height, street width/direction, pavement materials, green areas, pollutant concentration in air, and artificial heat emissions [5,7]. The wind speed was 2.20 m/s, and the background weather conditions during the survey. The average wind speed was 0.68 m/s at midnight (on 30 July 2019)

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