Selection of the probabilistic model of extreme floods: the case of the River Tiber in Rome

The probability distribution of the annual maximum peak flows on the River Tiber at the town of Rome (Ripetta) can be evaluated using the information available since the XV century. In this paper the probability distribution of two series of annual peak flows maxima observed at the Ripetta gauge is analysed: the systematic series, including all the data observed since the beginning of the systematic stage record in 1782, and the censored series of the exceptional floods that inundated the town of Rome, starting from the XV century. In order to find a criterion for choosing the ‘‘optimum” distribution law for the high return period quantiles, an index that takes into account both the accuracy and the uncertainty of the quantiles estimation is proposed.