Estimation of Extreme Rainfalls Using the DDF Curves for Han River Basin in Korea

The change of rainfall event and intensity from the global climate change are causing the needs of design criteria for infrastructures. The existing design criteria are decided by calculating the probable rainfall quantile through the frequency analysis. However, the actual rainfall record length at a point is usually shorter than desired return period. Therefore, in order to calculate the reliable design rainfall, the regional frequency analysis has been performed. In this study, a regional rainfall frequency analysis of the FORGEX (FOcused Rainfall Growth EXtension) method was applied to estimate the extreme rainfall quantiles, longer than 200 years of return period, by using the annual maximum rainfall data in Korea. The FORGEX method was adopted to make up for the problem the existing regional frequency analysis had contained the uncertainty for long return period. The DDF curves were derived by using data of 61 sites from the Korea Meteorological Administration (KMA). Moreover, the quantiles of FORGEX method were compared with the estimation extreme rainfall of At-site method and Index-flood method. In order to resolve the uncertainty problem of long return period, the need of research about the FORGEX method was confirmed.