Hydrological modelling and parameterization of cities, flood resilience

The constant evolution of cities can be seen as the urbanisation of the still available areas. This introduces complex effects with respect to the balance of water. In addition, the highly variable nature of the climate and weather can easily exacerbate the extremes (including floods) thus influencing the water balance. The European Union considers that the management of flood risk is an appropriate strategy to replace conventional defense strategies against floods. This new strategy is a more holistic approach: it takes into account all the components at risk and seeks to reduce the vulnerability of receptors (people, buildings and infrastructures).Thus, resilience measures not only consist of individual technical solutions but they need to be integrated to a 'safety chain', which requires the development of resilience systems and tools. It is therefore essential to develop tools for assessing the performance of the latter, and at different scales. These concerns have help define the development of Multi-Hydro: interacting models already proven to represent different components of the water cycle to allow substantial progress in the modelling of urban water combined with ease use. Multi-Hydro is based on physical equations supported by distributed and coupled models. With a dedicated GIS MH-AssimTool, the geographical and physical information required for modelling are easily assimilated for each zone and at each resolution. Indeed, special attention was paid to the observables with the least scale dependence. Tools for multi-scale analysis are used to represent their variability at smaller scales than their own scales, thus allowing a more robust definition of hydrological parameterisations at different scales. All of these developments have been used to address the issues involved in flooding resilience at different urban system levels, within the framework of the European (Smartest, RainGain and BlueGreenDream) and national (Ville Numérique) projects, using a systemic approach on the scenarios of several case studies:- A small watershed Villecresnes (Val-de-Marne), used to assess the impacts of each change made in the model during its development.- The eastern part of the municipality of Saint-Maur-des-Fossés (Val-de-Marne ), has undergone a state audit of the drainage network (precise mapping of pipes and measurement campaigns). The preliminary results helped raise the issue of modelling rivers.- A district at Heywood (suburbs of Manchester, UK), has suffered several floods over the last decade and requires more detailed modelling in order to allow for the assessment of impact of four protection scenarios.- The catchment area of the Loup, whose outlet is connected to a runoff water storage tank, was modelled over four events of varying durations and intensities and helped start the validation of the model.- The Spaanse Polder area (Rotterdam , Netherlands), poses the problem of modelling very flat terrain with a complex drainage system (pumps and multiple outlets). This area will help to guide the future development of Multi-Hydro. In the context of improving the resilience of cities to flooding, Multi-Hydro is therefore placed as a tool that provides the ability to simulate scenarios for impact assessment at the basin scale of changes to smaller scales. Due to its ease of implementation at various scales conferred by MH-AssimTool and its modular structure and its free access property, Multi-Hydro is becoming a support decision tool