An urban trees parameterization for modeling microclimatic variables and thermal comfort conditions at street level with the Town Energy Balance model (TEB-SURFEX v8.0)

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.

Multi-layer coupling between SURFEX-TEB-V9.0 and Meso-NH-v5.3 for modelling the urban climate of high-rise cities

“…-The drag force due to high urban vegetation is not considered. It could be introduced similar to Santiago et al 2019, Redon et al (2020), or Krayenhoff et al (2020).…”

“…Meso-NH coupled with SURFEX-TEB-BEM is able to simulate the monthly average building-related anthropogenic heat flux with an overestimation of about 10%, which could be due to the positive temperature bias of 0 to 1 K at the urban stations for the simulation covering entirely May 2018. This is remarkable given the large number of uncertain input parameters related to urban morphology, building construction materials, capacity and coefficient of performance of air conditioning systems, building use, and occupant's behaviour (Masson et al, 2020).…”

Multi-layer coupling between SURFEX-TEB-v9.0 and Meso-NH-v5.3 for modelling the urban climate of high-rise cities

“…The 3-Published by Copernicus Publications on behalf of the European Geosciences Union. 5610 R. Schoetter et al: Coupling SURFEX and Meso-NH at multiple levels D building geometry directly influences the atmospheric flow (Moonen et al, 2012) in the urban roughness sublayer whose depth is about 2-5 times the characteristic building height (Roth, 2000). It also leads to the interception of solar radiation and the trapping of infrared radiation.…”

Understanding physical processes and feedback mechanisms between the urban surface and the overlying atmosphere

“…Therefore, in most UCMs the coupling between urban surface, trees and the UBL is incomplete. Yet, recent progress in the UCM community resulted in the addition of urban canyon vegetation in both single-layer (Redon et al, 2020) and multi-layer (Krayenhoff et al, 2020) UCMs. The integrated canyon vegetation can improve the representation of radiation interaction within the canyon (i.e.…”

“…The integrated canyon vegetation can improve the representation of radiation interaction within the canyon (i.e. shading effects), increase evaporative cooling, which can reduce heat stress, and decrease wind speeds due to increased canopy drag on the wind flow 6.7 Advection of TKE and its role in accurate representation of boundary-layer downwind of cities 123 (Krayenhoff et al, 2020;Redon et al, 2020). This is a great step towards better weather forecasts at the street scale (Ronda et al, 2017).…”