Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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A development of multivariate drought index using the simulated soil moisture from a GM-NHMM model

GM-NHMM 기반 토양함수 모의결과를 이용한 합성가뭄지수 개발

  • Park, Jong-Hyeon (Airfield Infra-Facilities Team, Incheon International Airport Corporation) ;
  • Lee, Joo-Heon (Department of Civil Engineering, Joongbu University) ;
  • Kim, Tae-Woong (Department of Civil and Environmental Engineering, Hanyang University) ;
  • Kwon, Hyun Han (Department of Civil and Environmental Engineering, Sejong University)
  • 박종현 (인천국제공항공사 운항시설처 비행장시설팀) ;
  • 이주헌 (중부대학교 공과대학 토목공학과) ;
  • 김태웅 (한양대학교 공과대학 건설환경공학과) ;
  • 권현한 (세종대학교 공과대학 건설환경공학과)
  • Received : 2018.10.16
  • Accepted : 2019.08.16
  • Published : 2019.08.31
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Abstract

The most drought assessments are based on a drought index, which depends on univariate variables such as precipitation and soil moisture. However, there is a limitation in representing the drought conditions with single variables due to their complexity. It has been acknowledged that a multivariate drought index can more effectively describe the complex drought state. In this context, this study propose a Copula-based drought index that can jointly consider precipitation and soil moisture. Unlike precipitation data, long-term soil moisture data is not readily available so that this study utilized a Gaussian Mixture Non-Homogeneous Hidden Markov chain Model (GM-NHMM) model to simulate the soil moisture using the observed precipitation and temperature ranging from 1973 to 2014. The GM-NHMM model showed a better performance in terms of reproducing key statistics of soil moisture, compared to a multiple regression model. Finally, a bivariate frequency analysis was performed for the drought duration and severity, and it was confirmed that the recent droughts over Jeollabuk-do in 2015 have a 20-year return period.

가뭄평가 시 단일 수문인자를 활용하여 가뭄지수를 산정하고 가뭄의 출현, 심도 및 지속기간 등을 평가하는 것이 일반적이다. 하지만 가뭄은 여러 요인이 복합적인 연관성을 가지며 나타나는 현상이므로 단일인자로 가뭄을 평가하는 경우 불확실성 및 한계가 존재한다. 이에 따라 다양한 수문기상 특성을 고려할 수 있는 가뭄지수의 개발이 지속적으로 요구되고 있다. 본 연구에서는 강우량 및 토양수분을 이용하여 가뭄을 평가하고자 은닉 마코프 모형(Hidden Markov chain Model)기반의 토양수분 모의기법을 통해 과거(1973-2014년) 토양의 수분함량을 모의하였으며, Copula 함수를 활용하여 강우량과 토양수분을 동시에 고려한 합성가뭄지수를 산정하였다. 본 연구에서 제안된 토양수분산정 모델은 다중 회귀 모형의 모의결과와 비교를 통해 모델의 적합성을 검증하였으며, 가뭄의 지속기간과 심도를 고려하여 이변량 빈도해석을 수행하였다. 이변량 빈도해석결과 2015년 전라북도 지역에 발생하였던 가뭄은 약 20년의 재현기간을 갖는 것으로 분석되었다.

Keywords

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