The GREENROOF module (v7.3) for modelling green roof hydrological and energetic performances within TEB

Abstract

Abstract. The need to prepare cities for climate change adaptation requests the urban modeller community to implement sustainable adaptation strategies within their models to be tested against specific city morphologies and scenarios. Greening city roofs is part of these strategies. In this context, the GREENROOF module for TEB (town energy balance) has been developed to model the interactions between buildings and green roof systems at the scale of the city. This module, which combines the ISBA model (Interaction between Soil Biosphere and Atmosphere) and TEB, allows for one to describe an extensive green roof composed of four functional layers (vegetation -grasses or sedums; substrate; retention/drainage layers; and artificial roof layers) and to model vegetation-atmosphere fluxes of heat, water and momentum, as well as the hydrological fluxes throughout the substrate and the drainage layers, and the thermal fluxes throughout the natural and artificial layers of the green roof. TEB-GREENROOF (SURFEX v7.3) should therefore be able to represent the impact of climate forcings on the functioning of green roof vegetation and, conversely, the influence of the green roof on the local climate. An evaluation of GREENROOF is performed for a case study located in Nancy (France) which consists of an instrumented extensive green roof with sedums and substrate and drainage layers that are typical of this kind of construction. After calibration of the drainage layer hydrological characteristics, model results show good dynamics for the substrate water content and the drainage at the green roof base, with nevertheless a tendency to underestimate the water content and overestimate the drainage. This does not impact too much the green roof temperatures, which present a good agreement with observations. Nonetheless GREENROOF tends to overestimate the soil temperatures and their amplitudes, but this effect is less important in the drainage layer. These results are encouraging with regard to modelling the impact of green roofs on thermal indoor comfort and energy consumption at the scale of cities, for which GREENROOF will be running with the building energy version of TEB -TEB-BEM. Moreover, with the green roof studied for GREENROOF evaluation being a type of extensive green roof widespread in cities, the type of hydrological characteristics highlighted for the case study will be used as the standard configuration to model extensive green roof impacts at the scale of cities.

Solar panels reduce both global warming and urban heat island

“…The focus is to keep the maximum of key processes, while making some approximations in the geometry that are pertinent at block scale (building shapes are averaged into road canyons, only one thermal zone is kept in the buildings, individual windows are averaged into a glazing fraction, etc.). Gardens and greenroofs modules have also been implemented (Lemonsu et al, 2012;DeMunck et al, 2013a). The modeling strategy chosen here for the implementation of solar panels is similar: key processes are kept while some geometrical assumptions are made to avoid unnecessary details of individual buildings.…”

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 model developments also permitted testing of implementing alternative urban energy systems; Masson et al (2014b) showed that solar panels could be widely implemented without adverse effect on the UHI (where a slight cooling, of approximately 0.2°C, was simulated). Air conditioning can increase night-time temperatures in more densely built parts of Paris by more than 1°C (De Munck et al, 2013), so a Building Energy Module is also a desirable component of the modeling system to evaluate anthropogenic heat fluxes to the atmosphere. Energetic human behavior has been including in TEB (Schoetter et al, 2017) thanks to a collaboration with sociologists ).…”

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)

“…Reversely, the microclimate within the canyon can be impacted by the modification of surface energy exchanges due to the presence of vegetation at the ground, especially by its evapotranspiration. A module of extensive green roofs was also developed (de Munck et al, 2013) still using the ISBA model to simulate the hydrological and energetic functioning of the green roofs, as well as the energy exchanges with atmosphere and the thermal coupling with the buildings on which they are installed.…”