Differential air temperature cooling performance of urban vegetation types in the tropics

Abstract

The tendency for cities to be warmer than surrounding rural areas, known as the urban heat island effect, has become a matter of increasing concern, particularly in regions with a hot, humid climate. While urban vegetation may reduce air temperatures, the magnitude of this cooling effect varies between different types of vegetation. In this study we compared the cooling effect of five vegetation types that are commonly encountered in the tropical city of Singapore: grass, shrub, managed trees, managed trees over shrub, and secondary forest. Ambient air temperatures were monitored over 18 months at 88 locations, and analysed in relation to characteristics of the surrounding vegetation. Generalised additive modelling revealed significant temperature reductions associated with increasing cover of managed trees, managed trees over shrubs below, and secondary forest vegetation, with the latter vegetation type having the greatest effect. We conclude that vegetation can significantly ameliorate temperatures in cities with a hot, humid climate, but not all types of vegetation are equally effective. By demonstrating the cooling benefits of secondary forest in densely-populated urban areas, public education and engagement campaigns could help overcome negative perceptions of such vegetation.