The aim of this study is to investigate and determine hydrologically homogeneous regions and to derive regional flood frequency estimates for 47 gauged sites in the West Mediterranean River Basins in Turkey, using an index flood method with L-moments parameter estimation. Screening of the data of the gauged site is carried out based on a discordancy measure in terms of the L-moments. Initial candidate regions are established by the cluster analysis of first five L-moment statistics, using k-means method. Homogeneity of the basins is tested using simulation with a four-parameter Kappa distribution and an L-moments based heterogeneity measure. Three subregions are defined, namely the Antalya subregion, the Lower West Mediterranean subregion, and the Upper West Mediterranean subregion. Comparative regional flood frequency estimates are made for each subregion using various distributions, namely the generalized logistic, general extreme value, generalized normal, Pearson type III, generalized Pareto, kappa, and Wakeby distributions. Based on an L-moments goodness-of-fit statistic, the Pearson type III distribution is identified as the best-fit distribution for the Antalya and Lower-West Mediterranean subregions, and the Generalized Logistic for the Upper-West Mediterranean subregion. Monte Carlo simulation is used to evaluate the accuracy of the quantile estimates on the basis of the relative root-meansquare error and relative bias.

Estimation of magnitude and frequency of extreme rainfall has immense importance to make decisions about hydraulic structures like spillways, dikes and dams etc. This research involves the estimation of regional rainfall quantiles of 23 sites using L-moment based index flood regional frequency analysis. Initially, different tests are applied to check the assumptions of independence, stationarity and identical distribution. An L-moment based discordancy measure is used to detect discordant sites. Since in Pakistan, highly elevated area receive more rainfall. On the basis of this characteristic, the study region is divided into three regions which satisfy the L-moment based heterogeneity statistics using Monte Carlo simulations from Kappa distribution. The regional quantile estimates are obtained from GEV, GNO and GLO distributions which are found to be best choices for all three regions based on L-moment ratio diagram, Z-Statistics and average weighted difference values. For robust regional estimates, some accuracy measures are calculated using a simulation study of regional L-moment algorithm. On the basis of relative bias, relative absolute bias and relative RMSE, GNO is found be best robust for regional quantile estimation at lager return periods of 50, 100, 500 and 1000 and GEV at return periods of 1, 2, 5, 10 and 20 for all three regions.

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This study investigates the regional analysis of annual maximum flood series of 48 stream gauging stations in the basins of the West Mediterranean Region in Turkey. The region is divided into three homogeneous subregions according to both Student‐t test and Dalrymple homogeneity test. The regional relationships of mean annual flood per unit area‐drainage area and coefficient of skew‐coefficient of variation are obtained. Two statistically meaningful relationships of the mean flood per unit area‐drainage area and a unique relationship between skewness and variation coefficients exist. Results show that the index‐flood method may be applicable to each homogenous subregion to estimate flood quantiles in the study area.