Abstract. In flow forecasting, additionally to the need of long time series of historic discharges for model setup and calibration, hydrological models also need real-time discharge data for the updating of the initial conditions at the time of the forecasts. The need of data challenges operational flow forecasting at ungauged or poorly gauged sites. This study evaluates the performance of different choices of parameter sets and discharge updates to run a flow forecasting model at ungauged sites, based on information from neighbour catchments. A cross-validation approach is applied on a set of 211 catchments in France and a 17-month forecasting period is used to calculate skill scores and evaluate the quality of the forecasts. A reference situation, where local information is available, is compared to alternative situations, which include scenarios where no local data is available at all and scenarios where local data started to be collected at the beginning of the forecasting period. To cope with uncertainties from rainfall forecasts, the model is driven by ensemble weather forecasts from the PEARP-Météo-France ensemble prediction system. The results show that neighbour catchments can contribute to provide forecasts of good quality at ungauged sites, especially with the transfer of parameter sets for model simulation. The added value of local data for the operational updating of the hydrological ensemble forecasts is highlighted.

A comparative analysis is conducted to assess the quality of streamflow forecasts issued by two different modeling conceptualizations of catchment response, both driven by the same weather ensemble prediction system (PEARP Météo-France). The two hydrological modeling approaches are the physically based and distributed hydrometeorological model SIM (Météo-France) and the lumped soil-moisture-accounting type rainfall-runoff model GRP (Cemagref). Discharges are simulated at 211 catchments in France over 17 months. Skill scores are computed for the first 2 days of forecast range. The results suggest good performance of both hydrological models and illustrate the benefit of streamflow data assimilation for ensemble short-term forecasting.

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Le partage de l’eau abordé dans cet article se concentre principalement sur le système Durance-Verdon alimentant directement la concession régionale de la Société du Canal de Provence. Ces rivières constituent également les principales ressources en eau superficielles de la Provence. Le système est composé d’infrastructures hydrauliques importantes : d’abord de stockage sur la Durance amont (Serre-Ponçon) et sur le Verdon amont (Castillon et Sainte-Croix), ensuite de transfert vers le reste de la Région, notamment sur les zones littorales méditerranéennes fortement peuplées. Les grandes retenues en amont du bassin sont en grande partie sous la concession d’EDF, la SCP étant concessionnaire du canal de Provence, dont les ressources en eau sont principalement issues du Verdon. La SCP a la responsabilité de l’acheminement et de la distribution des eaux dans toute la Région PACA jusque dans les Alpes-Maritimes. Dans sa gestion quotidienne de la ressource en eau, la SCP veille à une gestion rationnelle de la ressource et est tournée vers l’économie d’eau afin de se prémunir au mieux du changement climatique et de ses incertitudes.