The IF model was developed by Vito Iacobellis and Mauro Fiorentino and is based on a theoretical rationale for deriving the probability distribution of floods and help in understanding the physical processes underlying the distribution itself . The model presents a number of original assumptions based pn the following ideas: (1) The peak direct streamflow Q can always be expressed as the product of two random variates, namely, the average runoff per unit area ua and the peak contributing area a; (2) the distribution of ua conditional on a can be related to that of the rainfall depth occurring in a duration equal to a characteristic response time ta of the contributing part of the basin; and (3) ta is assumed to vary with a according to a power law. Consequently, the probability density function of Q can be found as the integral, over the total basin area A, of that of a times the density function of ua given a. It is suggested that ua can be expressed as a fraction of the excess rainfall and that the annual flood distribution can be related to that of Q by the hypothesis that the flood occurrence process is Poissonian. In the model it is assumed that a and ua are gamma and Weibull distributed, respectively. The model was applied to the annual flood series of severeal gauged basins in Southern Italy. The results showed strong physical consistence as the parameters tended to assume values in good agreement with well consolidated geomorphologic knowledge and suggested a new key to understanding the climatic control of the probability distribution of floods.