The cause of this undersimulation effect can be seen by examining the effects of increasing sampling interval of precipitation. An example is shown in Figure 2 for ten second and one hour sampling intervals. This figure demonstrates the smoothing effect of less frequent sampling. Likewise, the duration of periods with rain is increased, in this case from 7.6 hours to 11 hours. Comparison of precipitation signal for sampling at ten seconds and one hour.
Signal is considerably smoother at longer sampling intervals.
Since the degree of error exhibited in some of these experiments is unacceptable for realistic modeling, model calibration is needed to compensate for this undersimulation. By adjusting model parameters, the model can produce more realistic runoff results. Figure 3 compares the calibration results for all three models. In this figure, the calibrated parameters have been normalized by the true parameter value to allow intercomparison between models. All three models require parameter adjustments to model soils as less pervious to compensate for undersimulation at longer sampling intervals.