The 8 and 9 September 2002 flash flood event in France: a model intercomparison

Within the framework of the European Interreg
IIIb Medocc program, the HYDROPTIMET project aims
at the optimization of the hydrometeorological forecasting
tools in the context of intense precipitation within complex
topography. Therefore, some meteorological forecast models
and hydrological models were tested on four Mediterranean
flash-flood events. One of them occured in France where the
South-eastern ridge of the French “Massif Central”, the Gard
region, experienced a devastating flood on 8 and 9 September
2002. 24 people were killed during this event and the
economic damage was estimated at 1.2 billion euros.
To built the next generation of the hydrometeorological
forecasting chain that will be able to capture such localized
and fast events and the resulting discharges, the forecasted
rain fields might be improved to be relevant for hydrological
purposes.
In such context, this paper presents the results of the evaluation
methodology proposed by Yates et al. (2005) that highlights
the relevant hydrological scales of a simulated rain
field. Simulated rain fields of 7 meteorological model runs
concerning with the French event are therefore evaluated for
different accumulation times. The dynamics of these models
are either based on non-hydrostatic or hydrostatic equation
systems. Moreover, these models were run under different
configurations (resolution, initial conditions). The classical
score analysis and the areal evaluation of the simulated rain
fields are then performed in order to put forward the main
simulation characteristics that improve the quantitative precipitation
forecast.
The conclusions draw some recommendations on the value
of the quantitative precipitation forecasts and way to use it for
quantitative discharge forecasts within mountainous areas.