Improving the structure of a hydrological model to forecast catchment response to intense rainfall

Abstract

We compared the flood forecasts issued by a model used by operational services in France (GRP) and by a model developed to improve the simulation of floods resulting from intense rainfall (GR5H_RI). We selected 10,652 flood events from 19 years of hourly data available for 229 French catchments. The models were combined with a state-updating procedure to produce forecasts at 3, 6, 12 and 24 h lead times. Results indicate that the GR5H_RI model performs better on average than the GRP model at all lead times, particularly for forecasting flash floods (rise time < 12 h), which occur mainly in summer and early autumn. The use of the last observed streamflow to update initial conditions does not compensate for GRP’s structural errors in the case of fast catchment response to intense rainfall. The new structure therefore opens valuable operational perspectives.