The Influence of Planting Arrangement on Outdoor Thermal Comfort

A simulation study in a tropical urban public square

Abstract

Vegetation provides significant benefits for urban thermal environments attracting people to open spaces. Especially in tropical climates, squares are more vulnerable to thermal discomfort due to surrounding buildings and increased hard surface coverage compared to urban parks. Since the space for planting is limited, a proper arrangement is essential to enhance the outdoor thermal comfort (OTC). Nevertheless, the impact of different planting arrangements on OTC has not yet been adequately discovered in tropics. This research conducts numerical simulations using ENVI-met software employing physiological equivalent temperature (PET) to understand how planting patterns affect microclimate and OTC at pedestrian level (1.5m) under clustered, scattered, and equally distributed planting arrangements. The methodology includes three stages; onsite measurements, assessment of existing OTC level, and comparison of the impact of planting arrangements on microclimate and OTC. The changes in the planting arrangements considerably affect OTC in urban outdoors altering the air temperature (Ta), wind speed (WS), mean radiant temperature (MRT), and relative humidity (RH). MRT and the WS are found as the most important parameters influencing thermal comfort, thus collaborating with previous studies. Equally distributed planting arrangement has a significant impact providing the highest comfort improvement (9.8 ℃ PET reduction) at the pedestrian level. Reduced canopy overlaps and planting densities, and improved homogeneous shade coverage and ventilation are suggested to overcome thermal discomfort. The cooling effect of native tree species should be assessed in future research. These results guide urban designers and landscape architects in improving microclimate and OTC in warm-humid cities.