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Effects of roadside trees and road orientation on thermal environment in a tropical city.

Zaki, Sheikh Ahmad; Toh, Hai Jian; Yakub, Fitri; Saudi, Ahmad Shakir Mohd; Ardila-Rey, Jorge Alfredo; Muhammad-Sukki, Firdaus


Sheikh Ahmad Zaki

Hai Jian Toh

Fitri Yakub

Ahmad Shakir Mohd Saudi

Jorge Alfredo Ardila-Rey

Firdaus Muhammad-Sukki


Emerging tropical cities are experiencing rapid population growth and development, which can greatly affect the thermal environments. The effects of roadside trees and road orientation on the outdoor thermal environment were investigated on four different roads in Kuala Lumpur, Malaysia. Field measurements were conducted to assess outdoor thermal environments, where the selection of sites was based on different roadside tree morphological features and road orientations. Outdoor air temperature (Ta), relative humidity (RH), globe temperature (Tg), wind speed (WS), and wind direction (WD) were measured. Absolute humidity (AH) was estimated based on relative humidity and air temperature. Planting dense canopy trees with an average sky view factor (SVF) of 0.07 reduced the mean radiant temperature (Tmrt) 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 (N–S) and Northeast–Southwest (NE–SW) orientated 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 useful for urban road design in tropical cities in order to improve the outdoor thermal environment and pedestrian comfort.


ZAKI, S.A., TOH, H.J., YAKUB, F., SAUDI, A.S.M., ARDILA-REY, J.A. and MUHAMMAD-SUKKI, F. 2020. Effects of roadside trees and road orientation on thermal environment in a tropical city. Sustainability [online], 12(3), article 1053. Available from:

Journal Article Type Article
Acceptance Date Jan 24, 2020
Online Publication Date Feb 2, 2020
Publication Date 2020-02
Deposit Date Feb 5, 2020
Publicly Available Date Feb 5, 2020
Electronic ISSN 2071-1050
Publisher MDPI
Peer Reviewed Peer Reviewed
Volume 12
Issue 3
Article Number 1053
Keywords Field measurements; Roadside trees; Road orientation; Thermal environment; Thermal comfort; Physiological equivalent temperature
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