Thermal performance of standalone trees in different tropical weather conditions

Trees have been extensively used to reduce heat stress in hot weather conditions. However, the performance of each type of tree differs due to both its physical properties and the way it interacts with the prevailing climate conditions. In this paper we analyse by means of measurements the impact of six trees (Cynometra browneoides, Peltophorum pterocarpum, Garcinia celebica, Ficus kerkhovenii, Syzygium polyanthum, Samanea saman) on climate variables and thermal comfort levels in different weather conditions in the hot and humid climate of Singapore. Each tree was evaluated on two days during daytime. Sensors were deployed simultaneously under the tree crown and beside it (as a climatic reference site). Compared to previous studies, the quantitative results show a lower impact on air temperature and humidity. Impact on thermal comfort was notable although the thermal acceptability criterion was difficult to reach under the tree. Background air temperature and incoming solar radiation were the most important variables to predict thermal comfort levels under each tree, although the influence of the tree's leaf structure and the sky view factor was relevant. The outcomes of this work reveal the thermal impact (benefits and limitations) of stand-alone trees in hot and humid climates and provide grounded expectations for the purpose of improving thermal comfort.