Numerical simulation methods of tree effects on microclimate: A review

Trees provide shade, absorb and reflect solar radiation, and regulate air temperature and humidity through transpiration. Integrating these regulatory mechanisms into numerical simulations enables the analysis of their aerodynamic and thermal effects under various environmental conditions. However, trees not only modify the underlying surface properties but also influence turbulence and energy exchange with the surrounding environment, increasing the complexity of numerical simulations. Therefore, selecting appropriate numerical simulation methods is crucial for improving the accuracy and efficiency of simulations. This review focuses on the advantages, limitations, and applicable scenarios of numerical simulation methods for studying the impact of trees on the microclimate. It covers the energy and mass exchange between trees and the outdoor environment, the modeling of tree canopy morphologies, the treatment of governing equations (i.e., momentum, temperature, water vapor component, and turbulence transport equations), and the key parameter values within these equations. Additionally, the numerical simulation process of coupling the impact of trees on the microclimate with various energy balance equations is outlined. Relatively few studies have focused on the unsteady numerical simulation of the seasonal and diurnal variations in microclimate regulation by trees. There is also a lack of basic parameters of trees, making it challenging to reflect their dynamic regulation mechanisms. Obtaining accurate characteristic parameters of trees and key parameter values in the governing equations is crucial for the accuracy of numerical simulations. Furthermore, several challenging issues are discussed, aiming to provide insightful direction for future research.