Radiative shading effect of urban trees on cooling the regional built environment

•Urban trees are incorporated into an advanced single-layer urban canopy model.•Shading effect of trees is enabled by a Monte Carlo ray-tracing algorithm.•The fully-integrated WRF-urban modeling system with trees was applied to simulate.•Urban hydroclimate in an arid city.•The cooling effect of urban shade trees is found to be more prominent in nighttime.

Land use and land cover changes due to urbanization have led to significant modifications in the built environment at both local and regional scales, making adaptation/mitigation strategies imperative for the sustainable development of cities. While urban trees offer great potential for heat mitigation and enhanced environmental quality, most of the existing urban land surface models do not contain adequate representations of trees, particularly the radiative heat exchange in the canyons. In this study, we incorporated the radiative shading effect of urban trees into the state-of-the-art version of the coupled Weather Research and Forecasting-Urban Canopy Model modeling system. This modeling framework, albeit at its infancy, is applied to the Phoenix Metropolitan area to study the regional cooling effect of trees in an arid environment. Simulation results demonstrated the capacity of urban trees in reducing urban surface and air temperature by about 2 ∼ 9 °C and 1 ∼ 5 °C respectively and increasing relative humidity by 10 ∼ 20% during a mean diurnal cycle; the effect is more prominent during nighttime.