Consideration of documentary records in the Annals of the Choson Dynasty for the frequency analysis of rainfall in Seoul, Korea

In this study, flood records in the Annals of the Choson Dynasty (1392-1910) were considered for the frequency analysis of rainfall in Seoul, Korea. The old Korean rain gauge (Chukwooki) data (1777-1907) were also used to evaluate major flood records in the Annals of the Choson Dynasty. The design rainfalls were estimated using the binomial censored data maximum likelihood estimator. The results can be summarized as follows. (1) The frequency analysis was done for 24 h rainfall amounts as this was assumed to represent the three different rainfall records well: the documentary records in the Annals of the Choson Dynasty, the Chukwooki data and the modern data. Also, given the possible uncertainty level of the classification results of the documentary records, only 19 catastrophic events (the highest level of flood) were considered in the frequency analysis. The threshold value was decided to be 388 mm by comparing the documentary records with the Chukwooki data. (2) The sensitivity analysis shows that the effects of the threshold value, the number of catastrophic records, and the accuracy level of the flood records in the Annals of the Choson Dynasty on the frequency analysis results are very limited. That is, the length of the flood records in the Annals of the Choson Dynasty was found to be long enough to overcome the possible uncertainty of the flood records. (3) The design rainfalls estimated by taking into account the flood records in the Annals of the Choson Dynasty were found to be very similar to those for the modern data. However, the confidence intervals estimated by considering all the records available were found to be just one third of those of the modern data.