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LERAT ET AL.: VALUE OF UPSTREAM FLOW MEASUREMENTS X - 73. Mean areal rainfall P INT and potential evapotranspiration P E INT on the intermediatearea INT.95At the upstream station, corrupted and simulated flows will be noted ˜Q UPrespectively.and ˆQ UPNote that this paper only investigates flow simulation, not flow forecasting; thereforemodel updating and streamflow data assimilation algorithms are not considered here. Notealso that the question studied in this paper applies equally to all types of spatially explicit100hydrological models but for the sake of simplicity we will consider the simplest possibletel-00392240, version 1 - 5 Jun 2009105110scheme, i.e., a downstream catchment (TOTAL) with a single upstream subcatchment(UP) as shown in Figure 1. Figure 1In section 2, we review the existing practices on the use of upstream flow in rainfallrunoffmodels, as described in the literature. Section 3 details the three model versionsmentionned previously. Section 4 describes the catchment database on which the threemodels are applied. The results of the comparison between the three models are analyzedin section 5.2. Importance of upstream flow measurements in rainfall-runoff modelsIntegrating upstream discharges in rainfall-runoff models has two main interests. First,streamflow data on interior points provide spatial information on the hydrological processes,which may significantly improve the calibration when the model is distributedor semidistributed. Using upstream discharges in the calibration process can greatly reducethe risk of overparametrization by adding internal constraints on flow simulations.Jakeman and Hornberger [1993] and Perrin et al. [2001] discuss this issue of model overparametrization.Upstream discharges can be introduced through simultaneous calibra-D R A F T July 24, 2008, 3:43pm D R A F T