Implementation of street trees within the solar radiative exchange parameterization of TEB in SURFEX v8.0

Abstract

Abstract. The Town Energy Balance (TEB) model has been refined and improved in order to explicitly represent street trees and their impacts on radiative transfer: a new vegetated stratum on the vertical plane, which can shade the road, the walls, and the low vegetation has been added. This modification led to more complex radiative calculations, but has been done with a concern to preserve a certain level of simplicity and to limit the number of new input parameters for TEB to the cover fraction of trees, the mean height of trunks and trees, their specific leaf area index, and albedo. Indeed, the model is designed to be run over whole cities, for which it can simulate the local climatic variability related to urban landscape heterogeneity at the neighborhood scale. This means that computing times must be acceptable, and that input urban data must be available or easy to define. This simplified characterization of high vegetation necessarily induces some uncertainties in terms of the solar radiative exchanges, as quantified by comparison of TEB with a highspatial-resolution solar enlightenment model (SOLENE). On the basis of an idealized geometry of an urban canyon with various vegetation layouts, TEB is evaluated regarding the total shortwave radiation flux absorbed by the elements that compose the canyon. TEB simulations in summer gathered best scores for all configurations and surfaces considered, which is precisely the most relevant season to assess the cooling effect of deciduous trees under temperate climate. Mean absolute differences and biases of 6.03 and +3.50 W m −2 for road, respectively, and of 3.38 and +2.80 W m −2 for walls have been recorded in vegetationless canyons. In view of the important incident radiation flux, exceeding 1000 W m −2 at solar noon, the mean absolute percentage differences of 3 % for both surfaces remain moderate. Concerning the vegetated canyons, we noted a high variability of statistical scores depending on the vegetation layout. The greater uncertainties are found for the solar radiation fluxes received and absorbed by the high vegetation. The mean absolute differences averaged over the vegetation configurations during summertime are 21.12 ± 13.39 W m −2 or 20.92 ± 10.87 % of mean absolute percentage differences for the total shortwave absorption, but these scores are associated with acceptable biases: −15.96 ± 15.93 W m −2 .

How well does the local climate zone scheme discern the thermal environment of Toulouse (France)? An analysis using numerical simulation data

“…The modification of solar radiation by the buildings calculated by TEB has been evaluated by Redon et al . () using the building resolving model SOLENE as a reference. Their results show that TEB accurately simulates the radiation captured by the wall and the ground.…”

“…The explicit treatment of high vegetation implemented by Redon et al . () will circumvent this restriction in future versions of TEB. Similarly, for rural areas, the ISBA vegetation model employed here also only considers the vegetation at the surface.…”

Integrated urban services: Experience from four cities on different continents

“…ground vegetation, street trees, vegetated walls and green roofs). This required development of the TEB model (Masson, 2000) to consider, and further evaluate, such scenarios (Lemonsu et al, 2012;De Munck et al, 2013;De Munck et al, 2018;Redon et al, 2017). Using a complete vegetation and soil model to represent green roofs, De Munck et al (2018) showed that green roofs would not have a significant effect on air temperature at street level, contrary to ground vegetation and trees.…”

The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET v1.0): an efficient and user-friendly model of city cooling

“…κ watr is a complex function accounting for thermal stratification of water and surface friction velocity. To reduce complexity, and assuming a mixed homogeneous water layer, a constant κ watr is selected based on shallow lakes reported in Salas De León et al (2016). The change in temperature T ( • C) is the difference between the water temperature T surf,watr ( • C) and the soil temperature beneath the water layer T soil ( • C).…”

“…The Town Energy Balance (TEB) model (Masson, 2000) has emerged as a popular urban area parameterization scheme. The TEB-Veg (Lemonsu et al, 2012;Redon et al, 2017) variation includes urban vegetation and provides functionality to assess cooling impacts of GBI. However, the TEB-Veg model configuration and application requires a level of modelling skill normally outside the capability of environmental consultants.…”