A new hydro-climate model for urban water management including nature based solutions : a preliminary application on Paris metropolitan area

Cities are highly sealed resulting in less infiltration in the ground and so on in high quantities of runoff water and less evapotranspiration. A large part of stormwater is then drained by separate or combined sewer systems. In case of heavy rainfalls, stormwater can join directly the river, eventually leading to urban floods, or overflows through the combined sewer, then increasing the risk of river pollution. Allowing notably the study of water management and thermal comfort in cities, the Town Energy Balance (TEB) hydro-climatic urban model, constitutes a tool to evaluate adaptation strategies to urbanisation effects. Indeed, it makes it possible to study different nature based solutions scenarios (green-roofs, watering, ...). Few studies are modelling the combining effects of hydrology and micro-climate in cities while they are jointly involved in urban planning strategies. This study relies on a reconstructed sewerage network in the Paris metropolitan area adapted to the model resolution. Such a large area requires a specific multi-watershed calibration approach, rarely applied in urban areas. It will be based on the division of watersheds into hydrological response units. In light of an eighteen years simulation, an evaluation of the performances of the model (stormwater or combined flows) is performed using a multi-site objective function.