Comparative Analysis of Urban Heat Stress Mitigation Effects of Trees and Shade Structures

As urban heat island effects intensify with ongoing climate change, urban heat stress is increasing, posing a growing threat to the health of city dwellers. Common strategies for mitigating urban heat stress include tree planting and the installation of shade structures; however, studies comparing the effectiveness of these two strategies are limited. In this study, the Wet-Bulb Globe Temperature (WBGT) and air temperature (dry-bulb temperature, TA) were measured under direct sunlight, trees, and shade structures to evaluate and compare the heat stress mitigation effects of the two strategies. The results showed that WBGT and air temperature under trees were 0.8°C and 1.4°C lower, respectively, than under shade structures. From the perspectives of WBGT and air temperature, the shade structures' effectiveness reached only 84% and 76% of the trees' effect, respectively. This is attributed to the fact that trees cool the surrounding air through evapotranspiration, while shade structures may negatively impact the thermal environment due to longwave radiation emitted from the increased surface temperature. The findings indicate that trees are more effective than shade structures in mitigating heat stress, highlighting the importance of prioritizing tree planting over indiscriminate installation of shade structures as a more effective strategy for alleviating urban heat stress and adapting to climate change.