Urban trees are one of the most effective strategies to mitigate excessive heat stress in cities. To understand the underlying mechanisms of their cooling effect and to assess their use in urban planning, the accurate simulation of how trees interact with the ambient built environment is critical and imperative. However, the representation of urban trees in existing urban canopy models (in particular the single-layer ones) remains oversimplified. Here we develop a new Monte Carlo ray tracing method to explicitly resolve the canopy transmittance and evaluate its impact on radiative view factors between trees and regular building facets. The new method is highly accurate in reproducing analytical solutions. Sensitivity tests of radiative view factors suggest the importance of canopy transmittance in changing the radiation exchange. We then incorporate the ray tracing algorithm into the new version of the Arizona State University (ASU) Single-Layer Urban Canopy Model (ASLUM v3.1). In addition to radiation transmittance, ASLUM v3.1 explicitly resolves the radiative shading, evapotranspiration, and root water uptake of urban trees in street canyons, with significantly improved performance in predictions (especially latent heat flux) when compared to previous versions. We further apply ASLUM v3.1 to evaluate the impacts of trees with varying characteristics on urban radiation exchange and turbulent heat fluxes. Results show that urban trees reduce the net radiation of ground and wall as well as the daytime temperature via shading and transpiration, but may slightly warm the nighttime street canyons through radiative trapping effect.
|Journal||Building and Environment|
|Publication status||Published - 2021 Mar 15|
Bibliographical noteFunding Information:
This work was supported by U.S. National Science Foundation (NSF) under grant # AGS-1930629 . The authors would like to acknowledge the use of field observations from the BUBBLE, which was primarily supported by the Swiss Federal Office for Education and Science (Grant C00.0068 ).
This work was supported by U.S. National Science Foundation (NSF) under grant # AGS-1930629. The authors would like to acknowledge the use of field observations from the BUBBLE, which was primarily supported by the Swiss Federal Office for Education and Science (Grant C00.0068).
© 2021 Elsevier Ltd
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Civil and Structural Engineering
- Geography, Planning and Development
- Building and Construction