The effect of tree planting pattern on thermal comfort of pedestrians in urban streets: case of Ananda Coomaraswamy Mawatha, Colombo, Sri Lanka

Abstract

Street vegetation has an important impact on pedestrian thermal comfort, resulting in habitable urban street landscapes. As a result of industrialization and urbanization, unplanned developments along streets have become a cause of thermal discomfort for pedestrians. Since planting space is limited, proper arrangement is critical to improving Outdoor Thermal Comfort (OTC). The impact of diverse tree patterns on OTC has not yet been investigated. This study employs numerical simulations using ENVI-met 5.5.1 Bio-met software and The Predicted Mean Vote at 1.5 m above ground level on a sunny day at 2 pm to understand how planting patterns affect microclimate and OTC at pedestrian level (1.5m) when using different 8 tree patterns are suggested within the selected Local Climate Zone (LCZ) in Colombo. There is pattern1 to 8 with the base case scenario. The research method is divided into four stages: On-site measurements, Modelling of the research area, Assessment of existing microclimatic and thermal comfort conditions, and the Comparison of the impact of planting pattern on microclimate and OTC. Changes in tree patterns have a significant impact on OTC in urban environments, affecting Air Temperature, Wind Speed, Mean Radiant Temperature, and relative Humidity. MRT and WS have been identified to be the most critical characteristics influencing thermal comfort. Pattern2 has a significant influence at the pedestrian level, providing the maximum comfort increase (0.9 PMV reduction) to reduce thermal discomfort, reduced canopy overlaps with reduced canopy distance and the use of small tree category trees to get to planting densities, enhanced homogenous shadow covering and ventilation, are recommended. Future studies should look into the cooling effect of native tree species. These findings can help urban designers and landscape architects improve microclimate and OTC in warm, humid cities.