Abstract
Abstract. A good knowledge of rainfall is essential for hydrological operational purposes such as flood forecasting. The objective of this paper was to analyze, on a relatively large sample of flood events, how rainfall-runoff modeling using an event-based model can be sensitive to the use of spatial rainfall compared to mean areal rainfall over the watershed. This comparison was based not only on the model's efficiency in reproducing the flood events but also through the estimation of the initial conditions by the model, using different rainfall inputs. The initial conditions of soil moisture are indeed a key factor for flood modeling in the Mediterranean region. In order to provide a soil moisture index that could be related to the initial condition of the model, the soil moisture output of the Safran-Isba-Modcou (SIM) model developed by Météo-France was used. This study was done in the Gardon catchment (545 km2) in South France, using uniform or spatial rainfall data derived from rain gauge and radar for 16 flood events. The event-based model considered combines the SCS runoff production model and the Lag and Route routing model. Results show that spatial rainfall increases the efficiency of the model. The advantage of using spatial rainfall is marked for some of the largest flood events. In addition, the relationship between the model's initial condition and the external predictor of soil moisture provided by the SIM model is better when using spatial rainfall, in particular when using spatial radar data with R2 values increasing from 0.61 to 0.72.
Highlights
Flash floods are a very destructive hazard in the Mediterranean region
Radar rainfall measurements need to be corrected from rain gauges measurements, as stated by Creutin et al (1997), Hardegree et al (2008), and Wagener et al (2007)
The radar data were already corrected from rain gauges measurements, a new control was effected by a comparison of the rain gauge and gridded radar rainfall data
Summary
Flash floods are a very destructive hazard in the Mediterranean region They are caused by intense rainfall events inducing short flood rising times, usually several hours. Arnaud et al (2002) showed that using mean areal rainfall instead of spatially distributed rainfall tends to underestimate the volumes and the peak flows, when using the same calibration of the rainfall-runoff model. The possibility to recalibrate the model in order to get equivalents results with uniform or spatial rainfall as model inputs has been little investigated up to now. This question was addressed in the present study using an event-based rainfall-runoff distributed model
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