Comparative analysis of green actions to improve outdoor thermal comfort inside typical urban street canyons

Urban microclimate analyses are being used more and more to address the planning decision process to create livable and healthy public spaces. The study, conducted in collaboration with the municipality of Bilbao (Basque Country, Spain), presents a comparative analysis of green actions to improve outdoor thermal comfort conditions. The evaluation was performed in three typical urban street canyons characterized by different geometric proportions and five urban greenery scenarios in typical summer day conditions. For each scenario, the mean radiant temperature, relative humidity, air temperature, surface temperature and wind speed have been analyzed using ENVI-met model. The study quantitatively confirms that the vegetation elements such as grass, green roofs and trees, improves the thermal comfort at pedestrian level. Thermal comfort is assessed using the PET (Physiological Equivalent Temperature) thermal index. The highest PET reduction occurs by combining the presence of trees and grass, which can lead to a reduction of about two PET thermophysiological assessment classes during the daily maximum values. Additionally, the work demonstrates how aspect ratio and ground surface materials can affect the intensity and the duration of discomfort period (PET > 23 C). The outcomes will be used by the municipality of Bilbao to improve the actual planning recommendations.