Asymptotic Variance of Regional Growth Curve for Generalized Logistic Distribution

The index flood method was introduced by Dalrymple to overcome the difficulties to obtain reliable estimates of the quantiles from relatively short record length. However, the application of index flood method must account for the additional uncertainty due to estimation of index flood at site. One must account for the uncertainties of the quantile estimates and those associated with the index flood. In this study, the generalized logistic distribution is considered as a an appropriate model for regional frequency analysis in Korea based on the method of probability weighted moments under the assumption that the regional quantiles and the index flood at site are independent. An approximate formulation of the variance of the quantile is introduced to evaluate the uncertainty of the estimated growth curve.