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PICS: towards Integrated Nowcasting of Flash Flood Impacts
Flash-flood forecasting is of crucial importance in mitigating the devastating effects of flash floods. However, its development has suffered serious setbacks due to the large number of catchment areas affected, their small size (1 to 500 km2), their very short response time (limited to a few hours), and the limited knowledge of the assets at risk. The first operational flash flood warning systems have recently been set up in France (Vigicrues Flash) and other countries. Nevertheless, the capabilities of these systems can still be greatly improved (limited anticipation, restricted geographical coverage, unrepresented impacts).
In line with HIWeather’s objectives, the PICS project proposes a step forward by designing and evaluating integrated forecast chains capable of anticipating the impacts of flash floods within a few hours. This objective will be achieved through interactions between various scientific teams (meteorologists, hydrologists, hydraulic engineers, economists, sociologists) and operational stakeholders (civil security, local authorities, insurance companies, hydropower companies, transport network operators). The consortium (see below) also benefits from close links with the international communities involved in HyMeX (post-flood field investigations, understanding of the physical mechanisms of flash floods) and HEPEX (new hydrometeorological ensemble prediction techniques and data assimilation).

The integrated short-term forecasting (or nowcasting) chains designed within the framework of the project will include the following elements: high-resolution quantitative precipitation estimates and short-term precipitation forecasts (or nowcasts), highly distributed precipitation runoff models designed to simulate river flows under ungauged conditions, hydraulic models based on the digital terrain model for the delineation of potentially flooded areas, and finally several impact models to represent various socio-economic effects: insurance losses, flooding of critical infrastructures, and dynamic population exposure and vulnerability. Particular attention is paid to the coherence between the different components of these chains, in terms of variables used, spatial and temporal resolutions, scale of application and degree of uncertainty. A critical aspect of the project is also the validation of the results on the basis of case studies. Indeed, the context of small ungauged basins is generally synonymous with a severe lack of data. For this reason, a special effort is devoted in the project to the collection of appropriate validation data sets (impacts, flood areas, etc.) and the definition of relevant validation strategies. The project includes case studies related to recent extreme rainfall events observed in the French Mediterranean area in the last decade. The list of case studies results from exchanges with end users. The project also involves major efforts to improve and adapt the various components involved in the modelling chains: improvement of distributed hydrological modelling under ungauged conditions, qualification of uncertainties on flow estimates based on rainfall observations and nowcasting, improvement of 1-D approaches and testing of a 2-D model for large-scale automatic hydraulic calculations, and finally adaptation of impact models to take advantage of the information on flooded areas provided by the forecasting chain. Therefore, the project should enable significant progress to be made in the field of integrated nowcasting of the impacts of flash floods. The broad representation of potential end users in the project, as members of the end-user group and project partners, should finally facilitate the transfer of the project results to operational applications, and in particular to the Vigicrues Flash operational tool, covering the entire French national territory.

For more information about PICS, please vist https://pics.ifsttar.fr/en/

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