How do the soil, the vegetation and the weather affect the water content of a green roof ?

International audience ; In the last decade, soil imperviousness has been one of the main urban issues in the Northeast of France. In case of strong rain events, runoff can lead to the discharge of high volume of water and can cause water system saturation. Among all urban-water regulation systems, Green Roofs (GR) can be used to store and delay the release of rainwater to sewers [4]. GR are also considered as a sustainable solution that offers benefits such as building insulation, urban heat island cooling during summer and air pollution control.The hydrological performances of GR are directly linked to the outflow of a GR which is mainly related to the water content inside the layers. In order to investigate these performances, the water content needs to be measured and simulated. Few models exist to describe the hydrological behavior of soil and can be adapted for GR characteristics such as soil parameters of the different layers, dimension, type of vegetation, etc. In this study, the dynamic of the water content is described by two elements. The first element describes the hydrological infiltration throughout unsaturated porous media and is based on the Richards’ equation. This equation is solved by combination with the Van Genuchten - Mualem model which depends on soil parameters. The second element estimates the water extracted from the soil due to the vegetation and the weather conditions. All these models and equations are implemented in Hydrus-1D© software to simulate hydrological behavior [5]. This software allows the set up of the green roof structure, boundary conditions, meteorological data, soil and vegetation parameters in order to reproduce the green roof real conditions.However, some of the model parameters, as soil or vegetation parameters, are challenging to determine as they are difficult to measure accurately through experiments. All the parameter uncertainties are propagated to the simulation of water retention capacity and need to be analysed with Global Sensitivity Analysis (GSA). A first ...