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Better flood forecasting is possible!
04 August 2011
Irstea (formerly Cemagref)
A number of disasters, including Draguignan, Vaison-la-Romaine and the flooding of the Somme, Aude and Gard rivers, are there to remind us of the vulnerability of life and property to floods. For over 20 years, Cemagref scientists have developed forecasting tools to warn the public and the authorities and enable zones at risk to prepare.
GRP flood-forecasting software
For SCHAPI, Cemagref developed the GRP software designed to forecast river flooding. How? By using the rain observations and forecasts supplied by the Meteo-France network for the corresponding river basins and taking soil humidity into account. The software has already been tested in real time on a large number of rivers and can provide warnings ranging from a few hours to a few days depending on the response time of the river basin. The forecasts calculated by GRP are fed into the national flood-warning system (www.vigicrues.gouv.fr) that may be freely consulted on the internet.
Analogues used to enhance forecasting quality
Beyond a few days, quantitative forecasts of flow rates become very imprecise. Forecasts can be improved by looking in the meteorological archives for precipitation data on past situations similar to the forecast situations. In conjunction with the Flood Forecasting agencies, Cemagref has pursued previous work and shown that it is possible to provide a one-week flow-rate forecast for the large Saône and Seine river basins by coupling the precipitation forecast with the GRP model for rainfall and flow rates.
AIGA1 sounds the alert!
The AIGA system, developed by Cemagref and Meteo-France, uses data supplied by meteorological radars to estimate in real time the risks arising from rainfall and river flow rates over the entire French hydrographic network. AIGA compares the real-time data with information from reference databases on rainfall and flow rates to detect dangerous situations. Risk maps are drawn up every 15 minutes with a resolution down to the square kilometre. AIGA already supplies operational maps to the Flood Forecasting agencies along the Mediterranean coast, with which Cemagref is currently working to evaluate the system.
RHYTMME2 detects risks in mountain regions
In mountain regions, intense, spatially limited precipitations cause torrential flooding, land slides and, in the winter time, avalanches. The meteorological radar network, established in low-lying regions, does not cover mountain regions very well. Cemagref and Meteo-France are working together on the RHYTMME project to set up, in the southern Alps, a network of small, new-generation radars. Two are already operational on Mont Vial (department 06) and Maurel mountain (department 04) and two more will be deployed by 2013. The goal is to create a system for local risk managers capable of forecasting the natural hazards caused by precipitation.
1 AIGA: Geographic-information processing for flood alerts.
2 RHYTMME: Hydrometeorological risks in mountain and Mediterranean regions. The project is funded by the EU, French PACA region, French Ecology ministry and Cemagref.