Cooling effects of two types of tree canopy shape in Penang, Malaysia

Abstract

Shade trees provide a cooling effect by blocking sunlight, increased ambient air humidity and provide shade during the day. All trees cannot offer relief from the heat in the same amount. This study compared the shading effectiveness of two types of canopy shape (rounded and spreading) in the landscape of Universiti Sains Malaysia, Penang. There are four species selected for this study. Field measurement of microclimate conditions under the tree canopy and open spaces were repeated on a sunny day. The effect of trees shade on air temperature, surface temperature, relative humidity, solar radiation and solar transmission were also compared and related to the leaf area index (LAI). It was found that the air temperature under the canopy could be reduced between 0.67 °C to 2.55 °C, while the surface-soil temperature can be reduced between 3.23 °C to 8.15 °C. Tree species with higher LAI values, Swietenia macrophylla (Big leaf mahogany) and Tabebuia rosea (Tecoma) provide significantly more cooling than the other species. Reduction of surface temperature is positively correlated with leaf area index. This study shows that shade tree in tropical climates are helpful in improving the outdoor thermal comfort, cooling ground surface by encouraging more latent heat and reduces air temperature by encouraging more evapotranspiration. Thus, the selection of tree species with higher leaf area index value can maximize the benefits they provide to the surrounding area.