Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 4 2008 10.5194/hess-12-1039-2008 http://www.hydrol-earth-syst-sci.net/12/1039/2008/ http://www.hydrol-earth-syst-sci.net/12/1039/2008/hess-12-1039-2008.html http://www.hydrol-earth-syst-sci.net/12/1039/2008/hess-12-1039-2008.pdf 1039 1051 2008-07-30 The benefit of high-resolution operational weather forecasts for flash flood warning J. Younis S. Anquetin J. Thielen jutta.thielen@jrc.it Institute for Environment and Sustainability, European Commission DG Joint Research Centre, Ispra, Italy Laboratoire d'Etude des Transferts en Hydrologie et Environnement, Grenoble Université (CNRS, UJF, IRD, INPG), France In Mediterranean Europe, flash flooding is one of the most devastating hazards in terms of loss of human life and infrastructures. Over the last two decades, flash floods have caused damage costing a billion Euros in France alone. One of the problems of flash floods is that warning times are very short, leaving typically only a few hours for civil protection services to act. This study investigates if operationally available short-range numerical weather forecasts together with a rainfall-runoff model can be used for early indication of the occurrence of flash floods. <br><br> One of the challenges in flash flood forecasting is that the watersheds are typically small, and good observational networks of both rainfall and discharge are rare. Therefore, hydrological models are difficult to calibrate and the simulated river discharges cannot always be compared with ground measurements. The lack of observations in most flash flood prone basins, therefore, necessitates the development of a method where the excess of the simulated discharge above a critical threshold can provide the forecaster with an indication of potential flood hazard in the area, with lead times of the order of weather forecasts. <br><br> This study is focused on the Cévennes-Vivarais region in the Southeast of the Massif Central in France, a region known for devastating flash floods. This paper describes the main aspects of using numerical weather forecasting for flash flood forecasting, together with a threshold – exceedance. As a case study the severe flash flood event which took place on 8–9 September 2002 has been chosen. <br><br> Short-range weather forecasts, from the Lokalmodell of the German national weather service, are used as input for the LISFLOOD model, a hybrid between a conceptual and physically based rainfall-runoff model. 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