Flood forecasting in the Tiber catchment area: a methodological analysis

The most difficult step in hydrological forecasting is precipitation forecast, since rain is the most irregular and least predictable meteorological field. Numerical meteorological models are the main tool to forecast the precipitation field over river basins where floods may be expected. Object of this paper is a preliminary analysis of the appropriate methodological approach to flood forecasting in the Tiber River basin. An assessment of the flood forecasting skill of a meteorological limited area model, coupled with a lumped rainfall-runoff model, is performed. The main indications which seem to arise are that integral precipitation over the catchment area is adequately forecast in its time-evolution, but the total rainfall shows a systematic deficit with respect to observations.