Modelling the effects of spatial variability in rainfall on catchment response .2. Experiments with distributed and lumped models

Computational experiments are carried out with the rainfall field model described in Part 1 of this paper and a physically based distributed modelling system, the Systeme Hydrologique Europeen (SHE), to explore the interaction between spatial variability in rainfall and other factors controlling catchment response; both models have been calibrated for the small upland Wye catchment (area 10.55 km(2)). Simulated rainfall fields are used to provide fully distributed rainfall inputs to the SHE; the corresponding 'true' catchment responses are then compared with those derived from incomplete sampling of the rainfall fields. The differences in simulated peak discharges and runoff volumes are assessed as a function of antecedent catchment conditions, network density and the level of spatial correlation in the rainfall input. A piecewise linear transfer function model with an averaged rainfall input is used to approximate SHE responses to fully distributed rainfall inputs, to provide insight into simple lumped model performance.