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

摘要

The need to prepare cities for climate change adaptation requests the urbanmodeller 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, theGREENROOF module for TEB (town energy balance) has been developed to modelthe interactions between buildings and green roof systems at the scale ofthe city. This module, which combines the ISBA model (Interaction between SoilBiosphere and Atmosphere) and TEB, allows for one to describe an extensive greenroof composed of four functional layers (vegetation – grasses or sedums;substrate; retention/drainage layers; and artificial roof layers) and tomodel vegetation-atmosphere fluxes of heat, water and momentum, as well asthe hydrological fluxes throughout the substrate and the drainage layers,and the thermal fluxes throughout the natural and artificial layers of thegreen roof. TEB-GREENROOF (SURFEX v7.3) should therefore be able torepresent the impact of climate forcings on the functioning of greenroof vegetation and, conversely, the influence of the green roof on thelocal climate. An evaluation of GREENROOF is performed for a case studylocated in Nancy (France) which consists of an instrumented extensive greenroof with sedums and substrate and drainage layers that are typical of thiskind of construction. After calibration of the drainage layer hydrologicalcharacteristics, model results show good dynamics for the substrate watercontent and the drainage at the green roof base, with nevertheless atendency to underestimate the water content and overestimate the drainage.This does not impact too much the green roof temperatures, which present agood agreement with observations. Nonetheless GREENROOF tends tooverestimate the soil temperatures and their amplitudes, but this effect isless important in the drainage layer. These results are encouraging withregard to modelling the impact of green roofs on thermal indoor comfort andenergy consumption at the scale of cities, for which GREENROOF will berunning with the building energy version of TEB – TEB-BEM. Moreover, with thegreen roof studied for GREENROOF evaluation being a type ofextensive green roof widespread in cities, the type of hydrological characteristics highlightedfor the case study will be used as the standard configuration to modelextensive green roof impacts at the scale of cities.