The shading effect of single trees on human thermal sensation during summer: a case study in Jeju, Republic of Korea

Abstract

This study aimed to analyze the shading effect of single trees on human thermal sensation (HTS) during summer. Micrometeorological data were collected and analyzed in both sunny and shaded locations for four tree species—one deciduous broadleaf tree (DBT), two evergreen broadleaf trees (EBT), and one evergreen coniferous tree (ECT) species. The results demonstrated relatively small differences in air temperature, relative humidity, and wind speed among the species, with mean values of 0.1–0.5 ℃, 0.5–1.8%, and 0.0–0.7 ms⁻¹, respectively. However, there was a significant difference observed in the mean radiant temperature, with a mean of 18.6 ℃. In terms of the HTS indices (PET and UTCI), the shaded locations exhibited mean reduction rates of 15.4–20.6% in PET, corresponding to a thermal perception reduction effect of 1.0–1.5 levels. The UTCI demonstrated a reduction effect of 9.7–12.5%, equivalent to a heat stress reduction effect of 0.6–0.7 levels. The ECT demonstrated higher mean reduction rates in PET, 1.3% and 3.5% higher than the DBT and EBT, respectively. However, the EBT presented a similar reduction effect on HTS as the ECT due to its high leaf density. Based on these findings, the mean radiant temperature and leaf density were found to be the primary factors influencing the heat reduction effects of single trees during summer. The findings of this study can serve as fundamental data for landscape planting methods that account for thermal environment improvement in the future.