Influence of Roadside Trees and Road Orientation on Outdoor Thermal Environment: Case Study in Kuala Lumpur, Malaysia

Abstract

Malaysia is experiencing rapid population growth and development, which can greatly affect outdoor thermal environments. Therefore, the influence of roadside trees and road orientation on outdoor thermal environment were studied on four different roads in Kuala Lumpur, Malaysia. Field measurements were carried out to evaluate outdoor thermal environments, where the selection of sites was based on different roadside tree morphological features and road orientations. Outdoor air temperature, relative humidity, globe temperature, wind speed, and wind direction were measured. Absolute humidity was estimated based on relative humidity and air temperature. Planting dense canopy trees with an average sky view factor of 0.07 reduced the mean radiant temperature by 35% and the physiological equivalent temperature (PET) by 25%. East–West (E–W) and Northwest–Southeast (NW–SE) oriented roads had high PET values of 41 °C and 43 °C, respectively. North–South and Northeast–Southwest oriented roads had lower PET values (37 °C), providing improved outdoor microclimate. Roadside trees provided greater cooling potential in E–W and NW–SE oriented roads. The findings are beneficial for urban road design in Malaysia to improve the outdoor thermal environment.KeywordsField measurementsRoadside treesRoad orientationThermal environmentPhysiological equivalent temperature