Quels apports hydrologiques pour les modèles hydrauliques? Vers ...

X - 8LERAT ET AL.: VALUE OF UPSTREAM FLOW MEASUREMENTS115tion on all discharge time-series via multi-objective functions [Madsen, 2003] or with asequential calibration on all individual subcatchments [Andersen et al., 2001, Das et al.,2008]. Whatever strategy is adopted, the literature converges toward a unanimous consensus:using upstream discharge data improves the simulations obtained with distributedand semidistributed models [Corradini, 1991, Michaud and Sorooshian, 1994]. However,120several questions remain unanswered:tel-00392240, version 1 - 5 Jun 20091251301. Many papers agree on the value of upstream flow measurements based on the analysisof isolated case studies, but they do not provide elements to generalize this result.What are the limits of this influence for an upstream station? Hydrological good sensewould suggest that the further upstream the station, the lesser its impact on downstreamsimulations. However, we lack a reference to estimate this impact quantitatively. Hence,the first objective of this paper is to detail the conditions necessary for measured upstreamflows to influence downstream simulations significantly.2. The impact of atmospheric data quality on model performance has been thoroughlystudied by many authors. For example, Oudin et al. [2006] analyzed the impact of biasedand randomly corrupted rainfall and potential evapotranspiration data on the performanceof lumped rainfall-runoff models. Only a few papers deal with the impact of the qualityof discharge data [Shrestha et al., 2007]. Moreover, these papers analyze situations wheredischarges constitute the calibration target and not a model input.The influence ofupstream flow data quality, when used as a model input, remains an open question and135constitutes the second objective of this paper.3. As mentioned in the introduction, using upstream discharges makes the modelerdependent on another input, which restricts the applicability of the models. A simpleD R A F T July 24, 2008, 3:43pm D R A F T