Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 4 2008 10.5194/hess-12-1141-2008 http://www.hydrol-earth-syst-sci.net/12/1141/2008/ http://www.hydrol-earth-syst-sci.net/12/1141/2008/hess-12-1141-2008.html http://www.hydrol-earth-syst-sci.net/12/1141/2008/hess-12-1141-2008.pdf 1141 1152 2008-08-26 Inferring the flood frequency distribution for an ungauged basin using a spatially distributed rainfall-runoff model G. Moretti A. Montanari alberto.montanari@unibo.it Independent Engineer, Stuttgart, Germany Faculty of Engineering, University of Bologna, Bologna, Italy The estimation of the peak river flow for ungauged river sections is a topical issue in applied hydrology. Spatially distributed rainfall-runoff models can be a useful tool to this end, since they are potentially able to simulate the river flow at any location of the watershed drainage network. However, it is not fully clear to what extent these models can provide reliable simulations over a wide range of spatial scales. This issue is investigated here by applying a spatially distributed, continuous simulation rainfall-runoff model to infer the flood frequency distribution of the Riarbero River. This is an ungauged mountain creek located in northern Italy, whose drainage area is 17 km². The hydrological model is first calibrated by using a 1-year record of hourly meteorological data and river flows observed at the outlet of the 1294 km² wide Secchia River basin, of which the Riarbero is a tributary. The model is then validated by performing a 100-year long simulation of synthetic river flow data, which allowed us to compare the simulated and observed flood frequency distributions at the Secchia River outlet and the internal cross river section of Cavola Bridge, where the basin area is 337 km². 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