On the uncertainty of a flood forecasting tool for small and medium size basins

When dealing with small and medium size basins the hydrologist is required to use meteorological predictions for flood forecasting. Merging meteorological and hydrological tools is necessary to give the due advance for civil defense actions.

In a strongly uncertain framework, such as that of small and medium scale basins, warnings must be issued in a probabilistic framework.

This work deals with the uncertainty of warnings related to a forecasting chain tailored for issuing flash floods. The propagation of uncertainty in the whole forecasting chain – starting from the rainfall volumes predicted by meteorological elaboration, ending with hydrologic evaluations, through the use of a multifractal disaggregation scheme (able to simulate rainfall fields at scales smaller than those of the Limited Area Models’ predictions) – is analyzed. The results are discussed on regional and site specific bases for some case studies in the Mediterranean area.