Representation of spatial variability of rainfall in aggregated rainfall-runoff models

The aggregated-precipitation input to a catchment is defined in this work as one that minimizes an objective measure of the difference between the calculated and the observed hydrograph. This measure is different from the evaluated mean areal precipitation using, for example, Thiessen polygons. Once the aggregated inputs are derived for a set of storm events over a given basin, the relationships between the mean areal precipitation, the precipitation at a point inside the basin, and the derived aggregated input may be analyzed to detect linkages among them. We represented this linkage by a weighting function, which multiplies single raingage records to obtain the aggregated input. Streamflow measurements and a simple model of the rainfall-runoff process are used to evaluate this weighting function, which varies during the storm. The ultimate goal of this work is to use this relationship to evaluate the aggregated input for ungaged storm events. In this preliminary phase, only linearly distributed and aggregated-input models were considered, coupled with rainfall fields generated from a stochastic space-time precipitation model. Results obtained by considering the distributed rainfall fields generated by a simpler version of the WGR model are presented, with reference to a catchment in Northern Italy.