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X - 6LERAT ET AL.: VALUE OF UPSTREAM FLOW MEASUREMENTStwo other models will be compared.It represents what can be achieved in a classicalsemidistributed scheme.2. A model (of the downstream station) called UP-Meas was calibrated and run in75validation mode with measured upstream discharges.3. A model (of the downstream station) called UP-Sim was calibrated using measuredupstream flows but run in validation mode with simulated upstream flows.We also tested the impact of introducing errors in the upstream flows. The analysisof the results is organised as follows: (i) the comparison between the benchmark andtel-00392240, version 1 - 5 Jun 2009808590the UP-Meas model on a large catchment data set gives insight on the conditions forupstream flow measurements to significantly influence downstream simulations; (ii) theimpact of the upstream flow quality is investigated by calibrating the UP-Meas model withcorrupted upstream flows, as described in section 5.2; and (iii) the comparison between section 5the benchmark and model UP-Sim quantifies the performance changes when upstreamflow measurements are replaced by the output of an upstream submodel.1.3. Notations and precisionsThe two nested stations divide the whole catchment (TOTAL) into an upstream part(UP) and an intermediate area (INT) drained between the outlets of UP and TOTALcatchments. Therefore, the discharges at the outlet of the TOTAL catchment are calculatedwith a model having five possible inputs (see Figure 1): Figure 11. Mean areal rainfall P UP and potential evapotranspiration P E UP on the upstreamsubcatchment UP,2. Measured discharge Q UP at the UP sub–catchment outlet,D R A F T July 24, 2008, 3:43pm D R A F T