Comparison of Various Tree Features for Blocking Solar Radiation in the Arid Urban Environment

Abstract

In the arid urban environment, pedestrians are often exposed to high amounts of solar radiation during summer, which can limit their activities. Shades are essential for reducing the harmful effects of solar radiation, particularly ultraviolet (UV) rays, which can be dangerous to human health. This study thoroughly evaluated the effect of various tree features for their efficacy in blocking solar radiation, especially photosynthetically active radiation (PAR) and ultraviolet A (UVA). Tree height, trunk height, canopy height and diameter, leaf area index (LAI), leaf size and type, planting techniques (individual and cluster), and agriculture services for eight common tree species used in the Landscape at King Abdulaziz University campus in Jeddah, KSA, were examined. Measurements were taken at noon when the solar zenith angle was perpendicular. The study found that the ability to block PAR and UVA varies based on several factors analyzed. Canopy height and diameter increased a tree's capability to block radiation, with pyramid-shaped trees and simple leaves being the most effective. Higher LAI, cluster planting, and removal of lower branches also increased a tree's radiation-blocking power. In conclusion, shade trees mitigate PAR and UVA and provide pedestrians with more opportunities to enjoy open landscapes in arid regions. KEYWORDS landscape planting, leave index, solar effect, trees benefits, ultraviolet radiation, arid environments