Assessment of the ENSO Impact on Rainfall Characteristics and Frequency Analysis in South Korea

Intensity-Duration-Frequency (IDF) curves are a form of frequency analysis used by engineers and scientists to create flood frequency estimations (Pilgrim, 2001). These frequency analyses are very important in the design of hydraulic structures to ensure that they are built economically and safely, that is, they are not over-designed or under-designed. IDF curves have traditionally been created by using historical data collected at a site and by assuming that this rainfall series is stationary and representative of the future. But as it has been proved in recent observations, climatic variability and trends do exist and their effects on rainfall have not been negligible. Increasing occurrences of the El Nino and La Nina phenomenon have lead to droughts and floods around the world, and long-term trends in rainfall have been seen in all regions across Korea. The purpose of this paper is to evaluate impacts of ENSO on rainfall characteristics and IDF curves in South Korea. In this paper, first, rainfall data in 60 climate stations were categorized into Warm (EL Nino), Cold (La Nina), Normal episodes based on the Cold & Warm Episodes by Season, then 100 years of daily rainfall data were generated for each episodic event (EL Nino, La Nina) using Markov chain Monte Carlo (MCMC) model. Finally, IDF curve analysis and comparison for each episode were conducted. From the results, it shows that there are significant changes in the rainfall characteristics and IDF curves among Warm (EL Nino), Cold (La Nina) and Normal episodes.