Abstract
The recently observed hydrologic extremes are unlike what has been experienced so far. Both the magnitude and frequency of extremes are important indicators that determine the flood safety design criteria. Therefore, how are design criteria updated faced with these extremes? Both a sudden increase of design rainfall by the inclusion of these extremes and complete ignorance are inappropriate. In this study, the changes in extremes were examined and an alternative way to estimate the design rainfall amounts was developed using the data from 60 stations in South Korea. The minimum density power divergence estimator (MDPDE) with the optimal value of a tuning parameter, α, was suggested as an alternative estimator instead of the maximum likelihood estimator (MLE); its performance was evaluated using the Gumbel (GUM) and the generalized extreme value (GEV) distribution. The results revealed an increase in both the frequency and magnitude of extreme events over the last two decades, which imply that the extremes are already occurring. The performance of the MDPDE was evaluated. The results revealed decreased and adjusted values of the design rainfall compared to MLE. On the other hand, the MDPDE of the GEV distribution with a positive shape parameter, ξ, does not show its advantage conditionally because the GEV distribution has a heavier right tail than the GUM distribution (ξ = 0). In contrast, the results showed the high sensitivity of the MLE to the extremes compared to MDPDE.
Highlights
On 31 August 2002, one of the most powerful typhoons hit South Korea, the 15th named storm in that year
The total rainfall on that day was 870.5 mm (34.27 in), which remains a record in South Korea
We introduce a minimum density power divergence estimator (MDPDE) which inherently possesses robust property against extreme values
Summary
On 31 August 2002, one of the most powerful typhoons hit South Korea, the 15th named storm in that year. Typhoon Rusa had record rainfall on Gangneung, a coastal city located on the east coast with a population of more than 215,000. The total rainfall on that day was 870.5 mm (34.27 in), which remains a record in South Korea. For multiple reasons including a relatively slow speed, the trajectory through the core part of the Korean Peninsula, the meteorological condition with a cold front facing the typhoon, the topological effect, and the untimely weather forecast [1,2], Typhoon Rusa caused record damage of approximately USD 5.5 billion since the establishment of the government in 1945 and 246 fatalities nationwide [3]
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