Abstract
Tropical cities can use urban greening designs featuring trees that provide shade and cooling in hot outdoor environments. The cooling effect involves numerous tree characteristics that are not easy to control during planting design, such as the canopy size and the optical properties of leaves. Planting the appropriate tree species dominates the cooling effects and the human thermal environment. Based on environmental and plant data, including the tree species, crown diameter of trees, physiologically equivalent temperature (PET), and sky view factor (SVF) in an outdoor space, a series of hierarchical cluster analysis (HCA) procedures was implemented to identify the tree species that are appropriate for improving thermal comfort. The results indicated strong correlations between SVF, average crown diameter, and PET. SVF decreased as the average crown diameter increased. For the average crown diameter of trees in an area wider than 1.5 m, the cooling effect was especially dominated by the tree species. Therefore, 15 species were screened by HCA procedures, based on a similar cooling effect. These species had various cooling effects, and were divided into four categories. Tree species, such as Spathodea campanulata and Cinnamomum camphora, had the appropriate crown diameter and cooling effect for the most comfortable thermal environment.
Highlights
Because outdoor environments in tropical areas are hot, people who engage in outdoor daytime activities tend to prefer outdoor areas shaded by trees, to outdoor areas that are not shaded by trees [1]
Small-leaved tree species tend to be more effective at cooling than larger-leaved species [12,13]
The tree database comprised 614 trees that were surveyed in the study area, and Table 1 shows the classification of tree species according to the average crown diameter
Summary
Because outdoor environments in tropical areas are hot, people who engage in outdoor daytime activities tend to prefer outdoor areas shaded by trees, to outdoor areas that are not shaded by trees [1]. A favorable tree planting design provides appropriate shade and cooling functions [2,3,4,5]. These functions influence microclimate modification, especially for tropical and subtropical regions [6,7,8], and improve thermal comfort [9,10,11]. Small-leaved tree species tend to be more effective at cooling than larger-leaved species [12,13]. The cooling effect and shading of plants is mainly determined by the canopy density, leaf arrangement, height, branch spread, bole height, solar radiation, and optical properties of the leaves [8,14,15]
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