Effects of Spatially-Distributed Rainfall on Runoff for a Conceptual Catchment

A physically-based rainfall-runoff model is used to investigate effects of moving storms on the runoff hydrograph of throughflow dominated idealised catchments. Simulations are undertaken varying the storm speed, direction, intensity, the part of the catchment affected by rainfall, and the spatial definition of rainfall zones. For a 100 km² catchment, under the circumstances investigated, an efficient spatial resolution of rainfall data is around 2.5 km along the path of the storm. Storms moving downstream produce earlier, higher peaks than do storms moving upstream. Error is most likely to be introduced into lumped-rainfall predictions for slower storm speeds, and the likely direction of this error can be specified. Differences in magnitude of peak response between downstream and upstream storm directions reach a maximum at a storm speed and direction similar to the average peak channel velocity. These results are qualitatively similar to those reported for overland flow dominated catchments, but differences in peak runoff between downstream and upstream storm directions are much smaller where rainfall inputs are modified by a period of hillslope throughflow.