• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.431-444
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• 2012

This study investigated the differences between annual maximum series and annual maximum independent rainfall event series with relatively short and long rainfall durations. Annual maximum independent rainfall events were selected by applying various IETDs and thresholds to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Annual maximum independent rainfall event series decided were then compared with the conventional annual maximum series. Summarizing the results is as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, the frequency of those with rather long durations decreased much higher. Second, The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Lastly, the difference between the annual maximum rainfall series and the annual maximum independent rainfall event series with rather short rainfall durations was found significantly large, which decreases with longer durations. This result indicates that the conventional data analysis method, especially for small basins with short concentration time, could lead an unrealistic design rainfall with little possibility of occurrence.

• Journal of Korea Water Resources Association
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• v.46 no.4
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• pp.361-372
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• 2013

This study used the beta distribution to analyze the independent annual maximum rainfall events from 1961 to 2010 and decided the representative rainfall event for Seoul. In detail, the annual maximum rainfall events were divided into two groups, the upper 50% and the lower 50%. For each group, a beta distribution was derived to pass the mean location of the rainfall peaks. Finally, the representative rainfall event was decided as the rainfall histogram of the arithmetic average of the two beta distributions derived. The representative rainfall event derived has a realistic shape very similar to those observed annual maximum rainfall events, especially with the higher rainfall peak compared to that of the Huff distribution. Comparison with other rainfall distribution models shows that the temporal distribution of the representative rainfall event derived in this study is most similar to the Keifer & Chu model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.137-147
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• 2010

In this study, Chukwooki and modern data were compared using annual maximum rainfall event series. Annual maximum series for specified rainfall duration in modern frequency analysis can not be constructed from Chukwooki data, so the concept of independent rainfall event is introduced to compare Chukwooki and modern data. Annual maximum rainfall event is determined by applying the bivariate exponential distribution and the parameters estimated annually are selected. The results using the annual parameter show that the hydrological meaning of the parameters is related to the variation of annual total rainfall amounts. For the whole independent rainfall events, the total rainfall and the rainfall intensity of Chukwooki data are greater than those of modern data, and rainfall duration of the two periods is similar. However modern annual maximum rainfall events show different characteristics that rainfall duration is much longer, rainfall intensity is similar and the total rainfall is greater than those of Chukwooki period. The increasing trend of rainfall duration and total rainfall of the modern annual rainfall events may be regarded as the one of components of the long-term cycle.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.127-136
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• 2011

In this study, annual maximum storm events are proposed to determined by the return periods considering total rainfall and rainfall intensity together. The rainfall series at Seoul since 1961 are examined and the results are as follows. First, the bivariate exponential distribution is used to determine annual maximum storm events. The parameter estimated annually provides more suitable results than the parameter estimated by whole periods. The chosen annual maximum storm events show these properties. The events with the biggest total rainfall tend to be selected in the wet years and the events with the biggest rainfall intensity in the wet years. These results satisfy the concept of critical storm events which produces the most severe runoff according to soil wetness. The average characteristics of the annual maximum storm events said average rainfall intensity 32.7 mm/hr in 1 hr storm duration(total rainfall 32.7 mm), average rainfall intensity 9.7 mm/hr in 24 hr storm duration(total rainfall 231.6 mm) and average rainfall intensity 7.4 mm/hr in 48 hr storm duration(total rainfall 355.0 mm).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.469-478
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• 2014

The annual maximum series (AMS) is usually used to estimate hydrological quantiles in practice because it is simple to construct and straightforward to probabilistic interpretation. However, it is limited to use the AMS in Korea due to the lack of reliable observed data which leads to the overestimation of design rainfall and/or flood. Using the 40-year observations of rainfall provided by the Korea Meteorological Administration, this study constructed the AMS and non-annual exceedance series (NAES) after identifying the independent storm event, analyzed the correlation between design rainfalls estimated from the AMS and NAES, and proposed a new method of point frequency analysis to estimate design rainfalls from the small number of observations.

• Journal of Korea Water Resources Association
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• v.45 no.6
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• pp.531-544
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• 2012

This study suggested the parameter estimation method for given rainfall events to be properly expressed by the beta distribution. For this purpose, this study compared the characteristics of probability density function with the parameter proposed considering the cases with and without addition to the rainfall peak, and the cases of using the real hyetograph and the rearranged hyetograph about the rainfall peak. As an example, this study analyzed the independent rainfall events at Seoul in 2010 and the annual maximum independent rainfall events from 1961 to 2010. The results derived are as follows. First, this study confirmed the necessity of additional consideration on rainfall peak to mimic the real hyetograph of rainfall events by the beta distribution. Second, this study confirmed the case of using rearranged hyetograph about the rainfall peak derived a better beta distribution to well mimic the characteristics of real rainfall than the case using the real hyetograph.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.137-146
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• 2011

In this study, annual maximum storm events are evaluated by applying the bivariate extremal distribution. Rainfall quantiles of probabilistic storm event are calculated using OR case joint return period, AND case joint return period and interval conditional joint return period. The difference between each of three joint return periods was explained by the quadrant which shows probability calculation concept in the bivariate frequency analysis. Rainfall quantiles under AND case joint return periods are similar to rainfall depths in the univariate frequency analysis. The probabilistic storm events overcome the primary limitation of conventional univariate frequency analysis. The application of these storm event analysis provides a simple, statistically efficient means of characterizing frequency of extreme storm event.