Flash Flood Forecasting with Coupled Precipitation Model in Mountainous Mediterranean Basin

Several types of precipitation models driven by radar data have been developed during the last few years. These models produce a spatially distributed rainfall forecasting suitable for hydrological needs. However, the assessment of their benefits and factors limiting their use in coupled hydrometeorological flood forecasting models (such as the response time of the basin, quality of the rainfall forecast, and rainfall forecast lead times) have not yet been analyzed in detail. This paper uses a case study to analyze the gain provided by a precipitation model for real-time flood forecasting in the case of a short response time basin (5-h lag time). The precipitation model, driven by radar and satellite data, is linked to a rainfall-runoff model that was previously set up and calibrated and is applied to the Gardon dʹAnduze (545-km^2) basin. Forecasts for lead times ranging from 1 to 4 h are used to assess the performance of the coupled model in flood forecasting from a hydrological perspective. The results from two rain events show that a 1-h lead-time rainfall forecast provides no additional improvement in flood forecasting compared with the simple persistence method. However, a real improvement is observed for the 2-h lead-time forecast. In the case of the 4-h lead time, the precipitation model essentially uses infrared satellite images and ground observations. The performance of the model for the 4-h forecast is not significantly better than the persistence method. However, for one of the two rain events, the model predicts the peak flow much better than the persistence method and the timing of the peak flow is also better. Because this work uses only a one-channel infrared satellite image, the 4-h forecast could be improved in the future when multiple-channel satellite estimates will be used.