MODELING 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 mode l 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 fac tors controlling catchment response; both models have been calibrated for the small upland Wye catchment (area 10.55 km(2)). Simulated rainf all fields are used to provide fully distributed rainfall inputs to th e SHE; the corresponding 'true' catchment responses are then compared with those derived from incomplete sampling of the rainfall fields. Th e differences in simulated peak discharges and runoff volumes are asse ssed as a function of antecedent catchment conditions, network density and the level of spatial correlation in the rainfall input. A piecewi se linear transfer function model with an averaged rainfall input is u sed to approximate SHE responses to fully distributed rainfall inputs, to provide insight into simple lumped model performance.