Heat-Mitigation Strategies to Improve Pedestrian Thermal Comfort in Urban Environments: A Review

Abstract

Thermal comfort is one of the main factors affecting pedestrian health, and improving thermal comfort enhances walkability. In this paper, the impact of various strategies on thermal-comfort improvement for pedestrians is thoroughly evaluated and compared. Review studies cover both fieldwork and simulation results. These strategies consist of shading (trees, buildings), the orientation and geometry of urban forms, vegetation, solar-reflective materials, and water bodies, which were investigated as the most effective ways to improve outdoor thermal comfort. Results showed that the most important climatic factors affecting outdoor thermal comfort are mean radiant temperature, wind speed, and wind direction in a microclimate. The best heat-mitigation strategy for improving thermal comfort was found to be vegetation and specifically trees because of their shading effect. The effect of height-to-width (H/W) ratio in canyons is another important factor. By increasing H/W ratio, the thermal-comfort level also increases. Deploying highly reflective materials in urban canyons is not recommended, as several studies showed that they could reflect solar radiation onto pedestrians. Results also showed that, in order to achieve a satisfactory level of thermal comfort, physiological and psychological factors should be considered together.