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RESEARCH PRODUCT

Flood Frequency Analysis for Sicily, Italy

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In this paper a regional flood frequency analysis based on the two-component extreme value TCEV distribution is developed using flood data recorded in Sicily. The hierarchical approach, characterized by three investigation levels for estimating the parameters of the theoretical distribution, is discussed first. The highest level of homogeneity hypothesis with regard to the skewness coefficient was verified by using a Monte Carlo technique and taking account of the separation effect proposed by Matalas et al. in 1975. This analysis also showed 1 the inability of the generalized extreme value model to reproduce the empirical cumulative distribution function CDF of the skewness coefficients, and 2 the convenience of using annual maximum peak flood data instead of annual maximum mean daily discharge records to estimate the parameters of the TCEV model. At the second level of regionalization, three different methods for identifying hydrologically homogeneous subregions are then performed: the first is based on the R-statistic test discussed by Wiltshire in 1986; the second is based on the hypothesis of statistical self-similarity of each selected area considering sampling statistical moments, discussed by Gupta et al. in 1994; and the third is founded on the same hypothesis of statistical self-similarity by using the sampling probability weighted moments discussed by Kumar et al. in 1994. The analysis showed that a further division into three subregions proposed by Cannarozzo et al. in 1995 is not necessary, and that a single theoretical growth curve is able to reproduce the empirical CDF of the standardized variable x. Finally, the third level of investigation showed that two different empirical relationships proposed for estimating the index flood x could be used for establishing the Q-T relationship anywhere in the region.