Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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A development of trivariate drought frequency analysis approach using copula function

Copula 함수를 활용한 삼변량 가뭄빈도해석 기법 개발

  • Kim, Jin-Young (Department of Civil Engineering, Chonbuk National University) ;
  • So, Byung-Jin (Department of Civil Engineering, Chonbuk National University) ;
  • Kim, Tae-Woong (Department of Civil and Environmental Engineering, Hanyang University) ;
  • Kwon, Hyun-Han (Department of Civil Engineering, Chonbuk National University)
  • Received : 2016.07.25
  • Accepted : 2016.08.26
  • Published : 2016.10.31
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Abstract

This study developed a trivariate Copula function based drought frequency analysis model to better evaluate the recent 2014~2015 drought event. The bivariate frequency analysis has been routinely used for the drought variables of interest (e.g. drought duration and severity). However, the recent drought patterns showed that the intensity can be regarded as an important factor which is being characterized by short duration and severe intensity. Thus, we used the trivariate Copula function approach to incorporate the trivariate drought characteristics into the drought frequency analysis. It was found that the return periods based on the trivariate frequency analysis are, in general, higher than the existing bivariate frequency analysis. In addition, this study concludes that the increase in drought frequency claimed by the Gumbel copula function has been overestimated compared to the Student t Copula function. In other words, the selection of copula functions is rather sensitive to the estimation of trivariate drought return periods at a given duration, magnitude and intensity.

본 연구에서는 최근 발생한 2014~2015 가뭄 사상을 보다 정확하게 분석하기 위해 삼변량 Copula 함수를 도입하여 연구를 진행하였다. 기존 연구에서는 일반적으로 가뭄 분석시 이변량(가뭄 지속시간, 심도)를 활용한 연구가 다수 진행되었다. 그러나 최근 강우자료의 패턴을 살펴보면 두 변량 이외의 가뭄 강도가 중요한 인자로 평가되어 이를 함께 고려한 삼변량 Copula 분석을 수행하였으며, 기상청 관측소 중 서울 관측소를 대상으로 연구를 진행하였다. 기본적으로, 이변량 빈도해석 결과에 비해 삼변량 해석 결과는 동일한 가뭄 사상에 대해서 다소 증가된 재현기간을 나타내는 것으로 파악됐다. 이와 더불어, Gumbel Copula 함수의 경우 Student t Copula 함수보다 가뭄 위험도 평가 시 다소 과대 추정하는 것으로 확인되었다. 즉, 삼변량 빈도해석 시 고려되는 Copula 함수의 선택이 가뭄의 재현기간을 추정하는데 있어 매우 민감한 사항으로 평가되었다.

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