Flood risks: a new national warning tool against flash floods for local authorities

Enhancing existing surveillance and warning measures for heavy rain and floods, the new Vigicrues Flash device is now operational, following 4 months of testing in 100 municipalities. Vigicrues Flash generates automatic warnings for mayors and common services, using voice messages, SMS and email, and based on estimates of the level of flood rarity that are updated every 15 minutes.

Tested and deployed in the Provence -Alpes-Côte d'Azur, Corsica region as part of the RHYTMME2 project, the AIGA method on which the new Vigicrues Flash warning system is based, has been adapted and expanded nationally. It is designed to provide improved forecasting of flash flooding in river basins that are often too small for their own measurement stations. This aim has been achieved by taking into account information supplied in real time by the meteorological radars of Météo-France and their transformation into river flows using a hydrological model developed jointly by Irstea and Schapi3.

Designed as a decision support tool for crisis situations to be used by decision-makers and managers, the AIGA method has one distinguishing feature: rather than providing information on the value of the phenomenon (rain, flow), it displays the rarity for an ongoing event. Information on the phenomenon is obtained in real time and cross-referenced with statistical information on the phenomenon in order to calculate the severity of the upcoming event (severe flood or very severe flood in Vigicrues Flash).

In addition to Vigicrues Flash, the AIGA method has been integrated into other tools designed for operational use: the APIC device (Heavy Rain Warnings for Municipalities)3, in use since 2011, and the RHYTMME (Hydrometeorological Risks in Mountain and Mediterranean Regions), in use since 2016.

As a research organization renowned for studying and managing risks linked to water for over 30 years, Irstea supports the implementation of flood prevention policies. At a time when communities are preparing to take on new responsibilities in 2018 (GEMAPI - the management of aquatic environments and prevention of floods), the use of the AIGA method as part of Vigicrues Flash, helps deal with these issues by using tools and methods perfected by Irstea.

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1 These measures include Vigicrues and the APIC tool: APIC (Heavy Rain Warnings for Municipalities) is a warning tool that uses email, SMS or voice message, created and run by Météo-France, announcing real-time observations of heavy rain over one or more mainland municipalities. Vigicrues is a flood monitoring mechanism designed and managed by Schapi and comprising a flood monitoring map and associated information reports and forecasts. Vigicrues indicates the level of monitoring required over the next 24 hours in relation to the risk of high water and overflows in government monitored rivers, providing real-time information about the level of these rivers and comparing them to benchmark flood levels, thus providing an understanding of expected developments over the coming hours.

2 The RHYTMME project (Hydrometeorological Risks in Mountain and Mediterranean regions), led jointly by Irstea and Météo-France in the PACA region, was used to perfect an internet mapping service to monitor heavy rain and associated hazards in real time.

3 Schapi - the French National Hydrometeorological and Flood Forecasting Center at the heart of the flood prevention department in the Ministry of the Environment - runs flood forecasting services and DREAL hydrometry units.