Scale-invariance laws in the recurrence interval of extreme floods: an application to the upper Po river valley (northern Italy)

The floods that have occurred in the upper valley of the Po river (northern Italy) were classified according to an index of strength on the basis of documentary sources available at the meteorological observatory of Moncalieri since 1780. The catalogue was ascertained to be complete only for events classified at least as moderate. Application of Cantor dust statistics and rank-ordering statistics to time-occurrences of floods provided significant evidence of scale-invariance laws that might be very helpful in assessing and reducing future hazards. The increase in the fractal dimension for floods occurring after 1890 is here related to the significant increase in the number of very heavy rainfall episodes measured all over Italy.