ABSTRACT
In water systems modelling, some of the forcing may be observed with a period larger than the typical reaction time of the catchment. A typical example is rainfall measured or forecasted on an hourly basis when the catchment response time is half an hour. In this case, using the (average) measured rainfall as the forcing functions directly as an
input to the model may lead to an underestimate of the amplitude of the model response (because the variations in the signal are 'missed' and smoothed out into the averaged measurement). This is particularly true for peak values in the output that are often related to peak values in the inputs. In order to estimate better the peak values of the model output, the inputs must be reconstructed at a time scale smaller than the typical reaction time of the hydrological system under study. Failing to generate an input at a smaller time scale than that of the catchment response time may introduce error/uncertainty in the model outputs. If a model with multiple inputs is being used (e.g. a catchment model using records from several rainfall gages) the spatial distribution of the inputs is also a source of uncertainty.
