Urban cooling factors: Do small greenspaces outperform building shade in mitigating urban heat island intensity?

Abstract

The effects of urban heat islands (UHIs) comprise one of the most challenging issues in mitigating excessive heat. Existing studies have reported cooling effects from small greenspaces (SGs) and building-shaded spaces (BSs). However, more empirical studies are necessary to fully investigate the role of SGs in heat reduction as a cooling solution for urban microclimatic design and planning. In addition, only a few previous studies have used field studies to examine the cooling effects of SGs and compare them to those of BSs. The purpose of this study was to assess the cooling degrees of SGs and BSs and compare them at the urban block level. Six urban blocks located in Seoul, South Korea were selected as the study area. Based on block size, the selected urban blocks were divided into three pairs featuring different sizes of greenspace. Air temperature was measured via a transect survey on six clear, hot summer days. Datapoints were then classified into three landcover types: SGs, BSs, and paved spaces (PSs) exposed to solar radiation. To measure the cooling effects and compare the air temperatures of each cooling factor, a series of T-tests and ANOVA tests were conducted, after performing a spatial analysis of each block. The result show that the cooling effects of SGs surpassed those of BSs. The SGs' cooling effects on blocks with larger greenspace were greater than those with small greenspace. In blocks with larger greenspace, SG's cooling benefits outweighed those of BSs. It is also notable that block size was a decisive factor affecting the magnitude of cooling degrees; SG brought the greatest microclimatic benefits for the largest blocks. Our findings will contribute to optimal cooling designs using SGs and BSs by illustrating where SGs should be included to facilitate cost-effective cooling.