A semi-distributed approach to rainfall-runoff modelling—a case study in a snow affected catchment

A semi-distributed hydrological model was applied to a small forested catcment in southern Finland. The aim was to demonstrate how differences in terrain properties could be taken into account in modelling runoff generation, and to test how well the presented model simulated streamflow with only limited calibration. Modelling was based on subdivision of a catchment into topographically similar areas, which were identified from a digital elevation model. The water balance in each area was calculated using a hillslopescale model. Discharges from the set of hillsope-scale models were combined with the aid of a routing procedure to yield the total streamflow at the catchment outlet. The catchment receives approximately 30% of the annual precipitation as snow, and thus a snow model was required in winter periods. The presented semi-distributed model was capable of reproducing fairly well the measured streamflow when only two model parameters were calibrated against streamflow. The results suggested that unlike the cumulative runoff, the temporal variability of runoff response was affected by terrain topography. Only minor differences were detected in reproduction of streamflow between the semi-distributed model and a simple lumped model IHACRES used as a reference.