Comparative analysis of urban heat stress mitigation effects of trees and shade structures

As urban heat islands and extreme heat events intensify due to climate change, reducing heat stress in cities has become a critical issue. This study aims to quantitatively compare the thermal mitigation effects of an artificial shade structure and a single tree in pedestrian environments. Wet-bulb globe temperature (WBGT) and air temperature were measured under direct sunlight, a fixed shade structure, and a Zelkova serrata tree on the Seoul National University campus. Results showed that both shading strategies significantly lowered WBGT and air temperature compared to direct sunlight. The tree provided greater cooling, lowering WBGT by 0.6°C and air temperature by 1.0°C more than the structure. This difference was attributed to the tree’s evapotranspiration and multi-layered foliage, which blocks solar radiation. In contrast, the effectiveness of the shade structure, which lacks evaporative cooling, was limited by longwave radiation emitted from its heated surface. While artificial shading was effective and space-efficient, its thermal performance was approximately 88% (WBGT) and 84% (air temperature) of the tree’s result. Additionally, the tree offered broader environmental value, improving air quality, supporting biodiversity, and enhancing climate resilience. These findings highlight that trees play a dual role in both heat mitigation and long-term climate adaptation. Given the functional differences, selection or combination of different strategies should take into consideration site-specific constraints and planning goals. A hybrid approach that balances short-term measures and long-term ecological benefits is essential for future urban climate strategies.