A Multi-Layer Model for Transpiration of Urban Trees Considering Vertical Structure

Abstract

As the intensity of the urban heat island effect increases, the cooling effect of urban trees has become important. Urban trees cool surfaces during the day via shading, increasing albedo and transpiration. Many studies are being conducted to calculate the transpiration rate; however, most approaches are not suitable for urban trees and oversimplify plant physiological processes. We propose a multi-layer model for the transpiration of urban trees, accounting for plant physiological processes and considering the vertical structure of trees and buildings. It has been expanded from an urban canopy model to accurately simulate the photosynthetically active radiation and leaf surface temperature. To evaluate how tree and surrounding building conditions affect transpiration, we simulated the transpiration of trees in different scenarios such as building height (i.e., 1H, 2H and 3H, H = 12 m), tree location (i.e., south tree and north tree in a E-W street), and vertical leaf area density (LAD) (i.e., constant density, high density with few layers, high density in middle layers, and high density in lower layers). The transpiration rate was estimated to be more sensitive to the building height and tree location than the LAD distribution. Transpiration-efficient trees differed depending on the surrounding condition and plant location. This model is a useful tool that provides guidelines on the planting of thermo-efficient trees depending on the structure or environment of the city.

Geospatial Analysis of Urban Heat Island Effects and Tree Equity

“…This costs money and adds emissions that further fuel UHIE. Urban forests should be planned with surrounding building height, tree location, and vertical leaf area in mind (Yun et al, 2020). For shade cooling of common urban surfaces, surface material surrounding trees created a greater impact than tree species (Kaluarachichi et al, 2020).…”

Simulation of Heat and Water Transport on Different Tree Canopies: A Finite Element Approach

“…This allows the formulation of different models, single or multi-layered, to study the different phenomena in forest and plants canopies, some of which are harmful to human life quality. Several examples could be enunciated: an evaluation of the radiation that reaches the soil and tree transpiration as means to mitigate the urban heat island (UHI) [2], a study of trees resistance to wind loads, and efficiency evaluation of trees as windbreakers [3], formulation of a multi-layer model to estimate the radiation distribution inside the canopy [4], use of a high-resolution model to study the water stress in a forest mulch layering [5], estimation of heat and water fluxes in the soil layer [6].…”