Regional analysis of storm hydrographs in the rescaled width function framework

The kinematic parameters of the Width Function based Instantaneous Unit Hydrograph (WFIUH) are estimated for a variety of Italian basins. Different gauged catchments located within the Upper Tiber valley, some major tributaries of the Tiber river itself and the Amaseno river (Central Italy) were selected to perform a regional analysis of hillslope and channel velocities for catchments with different morphology and lithology. The analytical expressions adopted to determine the first and second moment of the WFIUH are revised taking into account the statistical dependence between hillslope and channel lengths. Velocities are estimated through a moment fitting procedure based on rainfall records, runoff data and on the metrics of the catchment. Larger lag times and travel time variances and smaller hillslope velocities are observed for catchments underlain by carbonaceous formations when compared to other basins. The values obtained for both hillslope and channel velocities appear always to maintain a physical meaning. Finally, the capability of the WFIUH as a tool for transferring hydrologic information and obtain the prediction of flow hydrographs in ungauged basins is evaluated. Two equations relating the kinematic parameters to some easily-available characteristics of the catchment (namely the average slope and the fraction of basin underlain by carbonaceous formations) are proposed.