Impact of tree locations and arrangements on outdoor microclimates and human thermal comfort in an urban residential environment

Trees serve as a valuable asset in the urban built environment. In an arid city like Phoenix, trees are one of the primary urban green infrastructures to ameliorate extreme heat stress. Because of the cost of water and space in the desert residential environment, designing the optimal tree arrangement to maximize overall thermal benefits for residential neighborhoods is important and necessary. In this research, we first simulated a real neighborhood with current tree arrangement in ENVI-met (a holistic three-dimensional model for the simulation of surface-plant-air interactions), and validated the reliability of ENVI-met models by comparing the simulated results with systematic temperature collection transects. Further, we evaluated and compared differences in outdoor microclimates and human thermal comfort by simulating different tree layouts (clustered, equal interval, or dispersed) in the same neighborhood. Tree benefits at individual building scale and neighborhood scale are also compared and discussed. Based on the simulation, an equal interval two trees arrangement provided the most microclimate and human thermal comfort benefits in the neighborhood due to the importance of shading in the hot arid desert environment, following by clustered tree arrangement without canopy overlap. These findings will help policy makers and urban planners offer better guidelines for planting and establishing residential trees to mitigate extreme heat in the hot arid residential environment.