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X - 24LERAT ET AL.: VALUE OF UPSTREAM FLOW MEASUREMENTScontribution from the intermediate area INT and the routed upstream runoff from theupstream subcatchment. The third panel of Figure 9 shows the difference between similarcomponents from the two models.Figure 9 reveals that both simulations are nearly identical (differences on TOTAL lower440than 2 m 3 /s) with compensations between the two components: lower routed upstreamtel-00392240, version 1 - 5 Jun 2009445450455flows from the benchmark model (negative difference on ROUT ( ˆQ UP ) on Figure 9) is Figure 9compensated by higher intermediate runoff (RR(P INT , P E INT ) on the same figure). Theuse of upstream flow data during the calibration adds internal consistency to the UP-Sim model with better simulations on the UP point compared to the benchmark (seeTable 3), ... but this is not sufficient to increase the quality of downstream simulations Table 3on the TOTAL point. The additional value of the knowledge on upstream flows usedduring the calibration process appeared negligible to simulate downstream flows withour semidistributed model. This result reveals how difficult it is to increase the quality ofspatially explicit models: potential compensations between the components may overcomethe marginal value of additional internal information.6. ConclusionIn this work, we have studied the value of upstream flow measurements to simulatedownstream flow with a semidistributed model. Several experiments were conducted toverify the well-known advantage of including upstream flow data in spatially explicithydrological models. The key results are:1. With a test on 192 nested catchments in a temperate climate showing a wide diversityof configurations, we confirmed the advantage of using upstream flow measurements asan additional input. Comparing a model using this input and a benchmark model runD R A F T July 24, 2008, 3:43pm D R A F T