Impact de l'utilisation de deux modèles hydrologiques différents sur les scores d'évaluation de la qualité des prévisions hydrologiques d'ensemble

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUInternational audienceAt operational flood forecasting centres, forecasters usually have to deal with forecasts issued by different models and combine them to support their decisions and communicate flood alerts to end-users. In this study a comparative analysis is conducted to assess the quality of streamflow forecasts issued by two different modelling conceptualizations of catchment response, both driven by the same weather ensemble prediction system. Weather forecasts come from the ensemble prediction system PEARP of Météo-France, which is based on the global spectral ARPEGE model zoomed over France. The model runs 11 perturbed members for a forecast range of 60 hours. The two hydrological modelling approaches used are: 1) the coupled physically-based hydro-meteorological model SAFRAN-ISBA-MODCOU developed at Météo-France and based on a fully distributed catchment model, and 2) the GRPE forecasting system developed at Cemagref and based on a lumped soil-moisture-accounting type rainfall-runoff model. The study is conducted on a set of about 250 gauging stations representative of a wide range of upstream catchment areas and hydro-meteorological conditions in France. The discharges simulated by both systems are compared over an 18-month period (March 2005-September 2006). Skill scores are computed for the first two days of forecast range and the performance of both hydrologic ensemble forecasting systems is assessed