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310plex hydraulic models are not so important in semi-distributed hydrologicalmodelling.4.4 Model Inputs and ParameterisationThe selected coupled model (Figure 2) relies on (i) a single hydraulic model on315the main river reach, (ii) a number of lumped RR models applied to the subcatchmentsproviding point lateral inflows to the river reach and (iii) an addi-tel-00392240, version 1 - 5 Jun 2009320325tional lumped RR model applied on the remaining area providing uniformlydistributed inflows. To calibrate all these components together, we need todefine which rainfall inputs will feed the RR models and how to parameterizethe overall scheme.Since this study focused on the two questions of lateral inflow definition anddiscretisation, we did not explore modelling options that introduce differentrainfall inputs and different levels of parameterisation complexity. The resultspresented in the literature agree on the value of rainfall input distribution overparameter distribution (see e.g. Ajami et al., 2004; Andréassian et al., 2004;Zhang et al., 2004). Accordingly, the modelling scheme adopted here relies onthe following elements:330• Mean areal rainfall is calculated from gridded rainfall data (see Section 3)for each sub-catchment. This means that N distinct hourly rainfall timeseries are used as input to the N lateral sub-catchment models.• The same set of GR4J parameters is used for all sub-catchments. As aresult, only six parameters have to be calibrated: the four parameters ofthe GR4J model and the two parameters of the linearised diffusive wave16