Abstract
Abstract. The Town Energy Balance (TEB) urban climate model has recently been improved to more realistically address the radiative effects of trees within the urban canopy. These processes necessarily have an impact on the energy balance that needs to be taken into account. This is why a new method for calculating the turbulent fluxes for sensible and latent heat has been implemented. This method remains consistent with the “bigleaf” approach of the Interaction Soil–Biosphere–Atmosphere (ISBA) model, which deals with energy exchanges between vegetation and atmosphere within TEB. Nonetheless, the turbulent fluxes can now be dissociated between ground-based natural covers and the tree stratum above (knowing the vertical leaf density profile), which can modify the vertical profile in air temperature and humidity in the urban canopy. In addition, the aeraulic effect of trees is added, parameterized as a drag term and an energy dissipation term in the evolution equations of momentum and turbulent kinetic energy, respectively. This set of modifications relating to the explicit representation of the tree stratum in TEB is evaluated on an experimental case study. The model results are compared to micrometeorological and surface temperature measurements collected in a semi-open courtyard with trees and bordered by buildings. The new parameterizations improve the modeling of surface temperatures of walls and pavements, thanks to taking into account radiation absorption by trees, and of air temperature. The effect of wind speed being strongly slowed down by trees is also much more realistic. The universal thermal climate index diagnosed in TEB from inside-canyon environmental variables is highly dependent and sensitive to these variations in wind speed and radiation. This demonstrates the importance of properly modeling interactions between buildings and trees in urban environments, especially for climate-sensitive design issues.
Highlights
The urban climate commonly refers to the modification of local climate by the urban environment
The improvement brought by Town Energy Balance (TEB)-Tree is noted for daytime hours: the simulated diurnal cycle is in better agreement with the observed one
The strategy is rather simple by maintaining the bigleaf approach for using the Interaction Soil– Biosphere–Atmosphere (ISBA) surface–vegetation–atmosphere transfer (SVAT) model, i.e., by calculating a single energy balance for natural covers, treated as a composite compartment
Summary
The urban climate commonly refers to the modification of local climate by the urban environment. The dynamic effects and energy exchanges associated with vegetation are not addressed, in particular soil evaporation and plant transpiration This is the case with the models LASER/F (Kastendeuch et al, 2017; Bournez, 2018), SOLENE-microclimate (Bouyer et al, 2011; Malys et al, 2014, extension of the SOLENE radiative model), or ENVI-met (Bruse and Fleer, 1998; Bruse, 2004) that take into account a set of radiative, energetic, hydrological, and dynamic processes, allowing a better description of the complex interactions within the urban canopy layer. It computes radiative exchanges by considering radiation absorption coefficients by vegetation according to the leaf area density profile It integrates a vegetation model for the calculation of water and energy exchanges including the sensible heat flux between foliage and air, the evaporation of water intercepted by foliage, and the transpiration of plants controlled by a stomatal resistance. The objective here is to propose a refinement of the already existing parameterization of urban vegetation and of energetic and aeraulic effects of trees
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