Effects of tree canopies on solar radiation filtration in a tropical microclimatic environment

Abstract

In tropical climates, outdoor open spaces are highly exposed to solar radiation. This influences the outdoor energy budget, leading to consequential thermal effects on the overall urban environment and the urban heat island. Tree canopies and vegetation can play a significant role in reducing the effects of heat in open outdoor spaces by filtering the incoming solar radiation before it reaches the ground surface. This paper discusses the comparative effectiveness of two types of tree namely, Mesua ferrea L. and Hura crepitans L in filtering the direct solar radiation based on tree physical characteristics. It comprises of two evaluation methods, namely (i) a field measurement programme using a net radiometer and other related instrumentations, and (ii) a computer-based sun-shading analysis using ‘Ecotect’ software. The results indicate that on the average the heat filtration under the canopies of Mesua ferrea L. species was found to be 93%, whilst that of Hura crepitans L. species was 79%. In terms of canopy transmissivity, leaf index, shade area and tree height the comparative figures are as follows: Mesua ferrea L. (5%, 6.1, and 35.1% and 6.72m) and Hura crepitans L. (22%, 1.5, 52.1% and 6.50m). Hence, a difference of 14% filtration capability for differences of 17% canopy transmissivity value, 4.6 value of leaf area index, 17% of shade area and 0.22m. Finally, the study shows that leaf cover, branching and twigs as well as structural form can significantly influence the intensity and quality of shade.