Setting up a French national flash flood warning system for ungauged catchments based on the AIGA method

Abstract

Abstract. Occurring at small temporal and spatial scales, flash floods (FF) can cause severe economic damages and human losses. To better anticipate such events and mitigate their impacts, the French Ministry in charge of Ecology has decided to set up a national FF warning system over the French territory. This automated system will be run by the SCHAPI, the French national service in charge of flood forecasting, providing warnings for fast-responding ungauged catchments (area ranging from ~10 tR a NPð ,W ZLOO WKHUHIRUH EH FRPSOHPHQWDU\ WR WKH 6&+$3, ¶V QDWLRQDO ³YLJLODQFH´ V\VWHP ZKLFK FRQFHUQV RQO\ JDXJHG FDWFKPHQWV 7KH )) ZDUQLQJ V\VWHP WR EH LPSOHPHQWHG in 2017 will be based on a discharge-threshold flood warning method called AIGA (Javelle et al. 2014). This method has been experimented in real time in the south of France in the RHYTMME project (http://rhytmme.irstea.fr). It consists in comparing discharges generated by a simple conceptual hourly hydrologic model run at a 1-km² resolution to reference flood quantiles of different (e.g., 2-, 10-and 50-year) return periods. Therefore the system characterizes in real time the severity of ongoing events by the range of the return period estimated by AIGA at any point along the river network. The hydrologic model ingests operational rainfall radar-gauge products from Météo-France and takes into account the baseflow and the initial soil humidity conditions to better estimate the basin response to rainfall inputs. To meet the requirements of the future FF warning system, the AIGA method has been extended to the whole French territory (except Corsica and overseas French territories). The calibration, regionalization and validation procedures of the hydrologic model were carried out using data for ~700 hydrometric stations from the 2002-2015 period. Performance of the warning system was evaluated with various contingency criteria (e.g., probability of detection and success rate). Furthermore, specific flood events were analysed in more details, by comparing warnings issued for exceeding different critical flood quantiles and their associated timing with field observations. The performance results show that the proposed FF warning system is useful, especially for ungauged sites. The analysis also points out the need to account for the uncertainties in the precipitation inputs and the hydrological modelling, as well as include precipitation forecasts to improve the effective warning lead time.

Assessing the exposure to floods to estimate the risk of flood-related damage in French Mediterranean basins

“…This small-scale resolution enables greater accuracy in flood warning. For more details, a paper is also available in Floodrisk on the subject [16].…”

Ensemble Flash Flood Predictions Using a High-Resolution Nationwide Distributed Rainfall-Runoff Model: Case Study of the Heavy Rain Event of July 2018 and Typhoon Hagibis in 2019

“…With the recent advancements in quantitative precipitation estimate (QPE) and quantitative precipitation forecast (QPF) models, large-scale flood forecasting systems have been developed (Emerton et al 2016). Such systems have been operated at the continental to nationwide scales; for example, the European Flood Awareness System (EFAS) (Bartholmes et al 2009; in Europe, the Community Hydrologic Prediction System (CHPS) in USA (Demargne et al 2014), the Hydrological Forecasting System (HyFS) in Australia (Hapuarachchi et al 2017), the Grid-to-grid Model (G2G) in England and Wales (Anderson et al 2019;Price et al 2012) and Scotland (Cranston et al 2012), and AIGA in France (Javelle et al 2016). For site-specific flood predictions at a fine scale, for example, EC-JRC provides a rainfall-driven flash flood indicator within the EFAS framework called the European Precipitation Index based on Climatology (EPIC) (Alfieri and Thielen 2015) and a runoff-driven indicator called the European Runoff Index based on Climatology (ERID) (Raynaud et al 2015).…”

Risk-Based Early Warning System for Pluvial Flash Floods: Approaches and Foundations

“…The so-called VigieFlash system, which is based on a hydrological event-based model, has been operating in France since 2017. By using the AIGA method, introduced by Javelle et al [30], the system provides, on the basis of radar rainfall data, simulations for river branches and, therefore, predictions of flash floods in watersheds of a few hundred km 2 . This EWS also focuses only on the flood hazard due to small rivers.…”