On the variation of frequency-based rainfall amounts: a case study for evaluating recent extreme rainfalls in Korea |
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| Authors: | J H?Ahn T W?Kim Email author" target="_blank">C?YooEmail author Y N?Yoon |
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| Institution: | (1) Department of Civil and Environmental Engineering, Seokyung University, Seoul, 136–704, Korea;(2) Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, AZ 95721, USA;(3) Department of Civil and Environmental Engineering, Korea University, Seoul, 136–701, Korea |
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| Abstract: | Extreme rainfall events recently occurring in Korea have been shown to change frequency-based rainfall amounts quite significantly. Regardless of the reason for these extremes, the general concern of most hydrologists is how to handle these events for practical applications in Hydrology. Our study aim is to evaluate these extremes with their effect on frequency-based rainfall amounts, especially if they can be assumed to be within normal levels. As there is no commonly accepted methodology to be applied to this kind of study, we follow simplified steps such as: (1) estimation of the climatological variance of frequency-based rainfall amounts, (2) estimation of confidence intervals of frequency-based rainfall amounts (lower and upper bounds for the 5 and 1% significance levels estimated using the climatological variance), and (3) evaluation of the effect of extra rainfall events on the frequency-based rainfall amounts. Twelve stations on the Korean peninsula are selected as they have relatively longer data length. The annual maximum rainfall data collected from 1954 to 1998 are used. From this study we concluded that (1) at least 30 years of data length should be used for the frequency analysis in order to assure the stability of the variance of frequency-based rainfall amounts, (2) the climatological variances estimated all range from 5 to 8% of the frequency-based rainfall amounts, and (3) even though the frequency-based rainfall amount seems to become extreme with seemingly abnormal events, it still remains under its upper bound for the 5 or 1% significance levels estimated using the climatological variance, as well as it decays exponentially to the normal level as extra events are added. Thus, we conclude that we do not need to panic over seemingly abnormal events occurring so far, but just need to consider the variability inherent in frequency-based rainfall amounts. |
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| Keywords: | Global warming Rainfall Frequency analysis Confidence limits Climatological variance |
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