PICS: Towards integrated now-casting of flash floods impacts – PICS

the ANR PICS project aims to design and evaluate flash flood nowcasting chains offering up to 6 hours of anticipation and including a direct estimation of the possible damaging effects. The project is based on the interaction between scientific teams with varied skills (meteorologists, hydrologists, hydraulicians, economists, sociologists) and operational bodies (civil security, local authorities, insurance companies, managers of hydroelectric works and networks transport).

The integrated short-range nowcasting chains designed in the project will combine (i) high resolution quantitative precipitation estimates and short range (0-6h) precipitation forecasts, (ii) highly distributed rainfall runoff models designed to simulate river discharges in ungauged conditions, (iii) DTM based hydraulic models for the delineation of potentially flooded areas, and (iv) several impacts models aiming to represent varied socio-economic effects: insurance losses, inundation of critical infrastructures, and also dynamic population exposure and vulnerability.

The project will work towards: effectively coupling these various modelling components, evaluating their uncertainties and complementarity, and finally assessing the capacity of such nowcasting chains to meet the end users needs based on relevant case studies.

The project is structured in four scientific work packages (cf. figure). It is organized around a central work package (WP 4 - Integration and experimentation), in which integrated forecasting chains will be designed, applied and evaluated on different case studies. The three other scientific work packages are positioned upstream with the objective in mind of improving, adapting, and evaluating uncertainties of the various key components to be incorporated in the integrated forecasting chains, namely:
• the short range (0-6h) precipitation and discharge forecasts (WP1), obtained by coupling the state-of-the-art very short-range precipitation forecasts from Météo-France with distributed hydrological models ;
• the methods for flood areas estimation (WP2), including DTM-based 1D and 2D hydraulic methods to convert flow rates into flood areas delineation and related water heights and velocities ;
• the socio-economic impacts modelling methods (WP3), which have to integrate information relative to the flood areas for the estimation of impacts of different nature.

The wide representation of potential end users in the project, as members of the end users group and as project partners, should finally facilitate the transfer of the project results towards operational applications.

Several scientific publications should be submitted on the different aspects developped in the project.

Flash-flood forecasting is of crucial importance to mitigate the devastating effects of flash-floods. However, its development has experienced serious setbacks, due to the large number of affected catchments, their small surface areas (1 to 500 km²), their very short response times (limited to a few hours), and the limited knowledge of the assets being exposed. First operational flash flood warning systems have recently been implemented in France and other countries. Nevertheless, the capacities of these systems can still largely be improved (limited anticipation, limited geographic coverage, impacts not represented). In this context, the PICS project proposes a step forward by designing and evaluating integrated forecasting chains capable of anticipating the impacts of flash-floods with a few hours lead-time. This objective will be reached through interactions between varied scientific teams (meteorologists, hydrologists, hydraulic engineers, economists, sociologists) and operational actors (civil security, local authorities, insurance companies, hydropower companies, transport network operators). The integrated short-range forecasting (or nowcasting) chains designed in the project will incorporate the following components: high resolution quantitative precipitation estimates and short range precipitation forecasts (or nowcasts), highly distributed rainfall runoff models designed to simulate river discharges in ungauged conditions, DTM based hydraulic models for the delineation of potentially flooded areas, and finally several impacts models aiming to represent varied socio-economic effects: insurance losses, inundation of critical infrastructures, and also dynamic population exposure and vulnerability. The project will work towards: effectively coupling these various modelling components, evaluating these components in terms of uncertainties and complementarity, and finally assessing the capacity of these nowcasting chains to meet the end-users needs. A particular attention will be put on the consistency across the various components of these chains, in terms of variables used, spatial and temporal resolutions, application scale, and degree of uncertainty. One critical aspect of the project will also be the validation of the results based on case studies. The small ungauged basins context, indeed, is generally synonym of serious data scarcity. For this reason, a particular effort will be devoted in the project to the gathering of appropriate validation datasets (impacts, flood areas, etc.) and to define relevant validation strategies. The project will include case studies related to recent extreme rainfall events observed in the French Mediterranean area: June 2010 floods in the Argens basin, September-October 2014 floods in the Gardons, Vidourle, Hérault and Lez watersheds, and October 2015 floods in several small basins in the Alpes Maritimes territory. This list of case studies will be complemented at the beginning of the project based on the exchanges with the end users. The project will also entail significant efforts to improve and adapt the different components involved in the modelling chains: improvement of distributed hydrological modelling in ungauged conditions, qualification of uncertainties on discharges estimates based on rainfall observations and nowcasts, improvement of 1-D approaches and test of a 2-D model for large scale automatic hydraulic computations, and finally adaptation of the impacts models to take benefit from information on flooded areas provided by the forecasting chain. Considering this work program, the project should enable significant breakthroughs in the field of integrated flash floods impacts nowcasting. The wide representation of potential end users in the project, as members of the end-users group and as project partners, should finally facilitate the transfer of project results towards operational applications.