REGIONAL RAINFALL AND FLOOD FREQUENCY-ANALYSIS FOR SICILY USING THE 2-COMPONENT EXTREME-VALUE DISTRIBUTION

This paper first presents a duration-dependent hypothesis regarding th e parameters of the two component extreme value (TCEV) distribution an d proposes a simple model to obtain the rainfall depth-duration relati onship both at ungauged sites and at short record gauged sites in the Sicilian region. Then, by using the annual maximum peak flood and the annual maximum mean daily discharge recorded in Sicily, a TCEV hierarc hical regional procedure is developed. An empirical estimation criteri on which links the mean annual flood with the watershed area, and a mo dified rational formula in which a mean runoff coefficient is introduc ed, are proposed. Finally, two relationships are established for estim ating the mean runoff coefficient, making use of the permeable watersh ed area and the wooded area.