• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.367-371
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• 2010

가뭄 발생원인은 기후학적인 인자(온도, 바람, 상대습도 등)들과 밀접한 관계를 갖고 있으나, 가장 큰 원인은 강수부족이라고 말할 수 있다. 따라서 가뭄은 정상수준 이하의 강수 상황이 연속적으로 발생하여 나타나며, 설정된 절단수준에 대해 가뭄의 지속기간, 심도, 발생간격 등을 정의한 후 이에 대한 시계열 분석을 수행하여 가뭄의 특성을 분석한다. 본 연구에서는 가뭄 절단수준의 변화에 따른 한반도 내 가뭄의 특성분석을 위하여 하나의 절단수준으로 고정된 경우의 가뭄특성과 각 년도 월별 특성을 고려하여 절단수준이 지속적으로 변화하는 경우로 구분하여, 가뭄특성의 변화를 분석하였다. 또한 위 두 가지 경우에 대해 각각 가뭄해소 여부를 판단하여 총 4가지 경우에 따른 가뭄 특성을 분석하였다. 가뭄 절단수준의 변화 및 가뭄 해소여부에 따른 한반도 내 가뭄 특성을 분석하기 위해, 가뭄의 지속기간, 심도의 기초통계량 등을 산정하여 비교 분석하였다. 본 연구는 한반도 내의 가뭄특성을 보다 정확하게 해석하기 위해서는 다양한 가뭄정의에 따라 가뭄 해석결과가 나타내는 상대적 차이를 비교할 필요성이 있음을 증명하였다.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.437-446
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• 2000

THe drought analysis is performed by applications of truncation level method and conditional probability concept for hydrologic time series in Han river basin. The distributed trend of conditional probability is determined using kriging method for the time series. This study uses daily flowrate, monthly rainfall, and daily high temperature data sets. The daily flowrate data of 12 years(1986~1997) is used for the analysis. Also, the 14 years' data sets(1986~1999) for monthly rainfall and daily high temperature obtained from the National Weather Service of Korea are used in this study. In the cases of flowrate and rainfall data sets, the estimated value corresponding to the truncation level is decreased as the truncation level is increased but in the high temperature data, the value is increased as the truncation level is increased. The conditional probability varies according to the observations and sites. However, the distributed trend of drought is similar over the basin. As a result, the possibility of the drought is high in the middle and lower parts of Han river basin and thus it is recommended the distributed trend of drought be considered when the plan or measures for drought are established.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.52-52
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• 2011

최근 지구온난화가 가속화되면서 전 세계적으로 기상재해가 급증하고 있다. 특히 강우패턴의 변화를 고려한 강수 전망 연구결과는 온실가스 농도 증가로 호우나 가뭄, 대설 등이 지역에 따라 서로 상반되는 변화를 가져올 가능성이 있으며, 우리나라의 경우도 극한강수의 발생빈도가 1990년대 후반 이래로 뚜렷하게 증가하는 경향을 보이고 있다. 현재 우리나라에서도 이러한 기후변화에 대비하기 위해 여러 가지 가뭄연구를 수행하고 있는 실정이다. 일반적으로 가뭄의 해석에는 그 목적에 따라 여러 가지 지표를 이용하여 가뭄을 정의하며, 그 중 강수 및 하천유량 등은 기상 및 수문학적 가뭄을 판단하기 위한 지표로 널리 사용되고 있다. 특히 강수의 부족은 가뭄의 주된 요인이라 할 수 있으며, 가뭄의 정량적 평가에 효과적으로 이용될 수 있다. 즉 평균수준(혹은 절단수준)을 설정하고 가뭄의 지속기간, 심도, 발생빈도 등을 정의한 후, 이를 시계열 분석하여 가뭄의 특성을 분석하는 것이다. 또한 가뭄은 지속기간과 심도를 주요 특성변수를 가지는 이변량 수문사상이므로, 이를 반영한 확률 및 통계학적 해석방법의 적용이 반드시 필요하다. 그러므로 본 연구에서는 우리나라의 가뭄특성을 가뭄지속기간과 심도의 이변량을 동시에 고려하여 지점별 가뭄빈도해석을 수행하였으며, 지역별 가뭄발생특성을 고려하여, 강우관측지점별 과거에 발생한 최대가 뭄사상에 대한 가뭄위험도를 계산하였다. 그 결과, 우리나라 지점별 미래에 연속되는 10, 50, 100, 150년에 따라 과거의 최대가뭄이 발생할 확률을 지도로 도시하여 지역적 가뭄위험도를 분석하여 가뭄위험지역을 예상하였다. 이는 우리나라 내 가뭄취약지역의 우선순위를 결정하고, 실제로 국가적인 차원에서의 장기적인 가뭄관리를 하는 데 있어, 가뭄취약지역별 차별성 있는 가뭄대응방안을 마련하는 데 있어서도 하나의 객관적 근거로 활용될 수 있을 것으로 판단된다.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.3 s.6
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• pp.89-99
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• 2002

Drought is a very difficult natural disaster to overcome because its beginning and end are not clear to define, and it is widely distributed in space and has long term persistence. The purpose of this study was to evaluate the drought at Mokpo using drought frequency formula suggested by Sharma(1997). The precipitation records for the period 1906-1999 at Mokpo meteorological station are used for drought analysis. The most severe drought year is found to be that of 1995, which is of the 30-year frequency, and 18 drought years are selected based on the 5-year drought frequency.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1211-1215
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• 2006

가뭄에 대한 대책을 수립하기 위해서는 가뭄의 심도 및 지속기간 등 가뭄특성을 산정하여 가뭄을 정량화 하는 것이 필요하다. 본 연구에서는 가뭄을 해석하기 위하여 강수를 이용한 표준강수지수(SPI, Standardized precipitation Index)를 이용하여 가뭄 특성을 산정하였다. 서울지점은 강수의 근대 관측 기간이 약 100년 정도(1907년 ${\sim}$ 2003년) 이기 때문에 측우기 자료를 이용하여 조선 말까지(1770년 ${\sim}$ 1907년) 자료를 확장하여 가뭄지수를 산정하였다. 산정된 SPI로부터 절단 수준법 개념을 이용하여 SPI의 -1이하를 가뭄으로 정의 하고, 연속된 가뭄으로부터 가뭄 심도 및 가뭄 지속기간을 구하였다. 가뭄의 지속기간과 심도를 이변수 감마 분포(Bivariate Gamma Distribution)를 이용하여 가뭄의 재현특성을 분석하였고, 가뭄의 지속기간만을 고려한 재현기간과 본 연구에서 산정된 이변수 가뭄 재현기간을 서로 비교하였다.

• Journal of Korea Water Resources Association
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• v.36 no.4
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• pp.561-573
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• 2003

This study has analyzed the drought return and duration characteristics using the monthly rainfall at Seoul, and compared them with those obtained by applying the Poisson process. The Standardized Precipitation Index (SPI) was used as the drought index along with the 10 month moving average for the rainfall smoothing. The thresholds applied for the analysis of drought were -1.00, -1.50, and -2.00. The drought return and duration characteristics derived from the analysis of observed data show that: (1) The moderate drought occurs every 2 years and lasts about 4 - 5 months. (2) The severe drought occurs every 3 - 5 years and lasts about 2 - 4 months. (3) The extreme drought occurs every 8 - 23 years and lasts about 1 - 4 months. Especially, the severe droughts (thresholds of -1.5 and -2.0) before the long dry period were found to have longer return periods but shorter durations than those after the long dry period. This seems to be because of the high variability of precipitation as well as the fact that no snowfall has been added for the winter precipitation before the long dry period. Finally, the comparison of results derived from the analysis of observed data and those derived by applying the Poisson process shows that the Poisson process well explain the return and duration characteristics of drought.

• Journal of Korea Water Resources Association
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• v.37 no.1
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• pp.13-19
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• 2004

This study shows the possible use of the Poisson process for the characterization of dry year return period and duration. For the analysis we used an annual precipitation data, which has been collected since 1911 in Seoul. The highest threshold for the application of the Poisson process was determined to be the mean-0.5standard deviation, and then the results from the Poisson process are compared with the observed. Especially, the Poisson process was found to reproduce the mean duration and return interval quite well and show the possibility of using the Poisson process for the drought analysis.

• Journal of Korea Water Resources Association
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• v.49 no.4
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• pp.275-282
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• 2016

The objective of this study is to propose a new method to determine the drought event and the design drought severity. In order to define a drought event from precipitation data, theory of run was applied with the cumulative rainfall deficit. When we have a large amount of rainfall over the threshold level, in this study, we compare with the previous cumulative rainfall deficit to determine whether the drought is relieved or not. The recurrence characteristics of the drought severity on the specific duration was analyzed by the conditional bivariate copula function and confidence intervals were estimated to quantify uncertainties. The methodology was applied to Seoul station with the historical dataset (1909~2015). It was observed that the past droughts considered as extreme hydrological events had from 10 to 50 years of return period. On the other hand, the current on-going drought event started from 2013 showed the significantly higher return period. It is expected that the result of this study may be utilized as the reliable criteria based on the concept of return period for the drought contingency plan.

• Journal of Korea Water Resources Association
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• v.39 no.4 s.165
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• pp.373-382
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• 2006

In this study a theoretical drought severity-duration-frequency analysis is performed based on a simple Rectangular Pulses Poisson Process Model(RPPM). Data set with various durations are prepared for a given truncation level, whose statistics are then derived to be used for parameter estimation. These parameters are then used for the theoretical drought severity-duration-frequency analysis. The analysis is considered for two cases; one is to consider the overlap probability and the other is not. The drought severity of considering the overlap probability increases more as the return period increases. However, the overlap probability itself decreases as the duration increases, which is because the occurrence probability of events decreases as the duration increases. Also, if the duration increases, the events rarely or even not occur, since parameters of the model cannot be estimated in those cases, so the drought severity may not be computed. This is an obvious limitation of the simple RPPM. In this study the return periods of the important drought events occurred in Seoul are estimated using the results of the study. If the return period of an event is assumed to be the longest one among those with various durations, the return periods of some important event in Seoul are estimated to be between 14 and 35 years. These return periods are not so long to indicate that these droughts can occur frequently.

• Journal of Korea Water Resources Association
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• v.40 no.4
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• pp.335-343
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• 2007

Drought characteristics need to be preceded before establishing a drought mitigation plan. In this study, using a Standardized Precipitation Index (SPI), a hydrologic drought was defined as an event during which the SPIs are continuously below a certain truncation level. Then, a methodology of drought frequency analysis was performed to quantitatively characterize droughts considering drought duration and severity simultaneously. The theory of runs was used to model drought recurrence and to determine drought properties like duration and severity. Short historical records usually do not allow reliable bivariate analyses. However, more than hundred years of precipitation data (1770 ${\sim}$ 1907) collected in Chosun Kingdom Age using an old Korean rain gage called Chukwooki can provide valuable information about past events. It is shown that a bivariate gamma distribution well represented the joint probabilistic properties of Korean drought duration and severity. The overall results of this study show that the proposed bivariate drought frequency analysis overcomes the drawbacks of the conventional univariate frequency analysis by providing a consistent representation of the drought recurrent property.