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Development of a surrogate model based on temperature for estimation of evapotranspiration and its use for drought index applicability assessment

증발산 산정을 위한 온도기반의 대체모형 개발 및 가뭄지수 적용성 평가

  • Kim, Ho-Jun (Department of Civil and Environmental Engineering, Sejong University) ;
  • Kim, Kyoungwook (Department of Energy Development, ISAN Corporation) ;
  • Kwon, Hyun-Han (Department of Civil & Environmental Engineering, Sejong University)
  • 김호준 (세종대학교 건설환경공학과) ;
  • 김경욱 ((주)이산 수자원본부 에너지사업부) ;
  • 권현한 (세종대학교 건설환경공학과)
  • Received : 2021.09.29
  • Accepted : 2021.10.29
  • Published : 2021.11.30

Abstract

Evapotranspiration, one of the hydrometeorological components, is considered an important variable for water resource planning and management and is primarily used as input data for hydrological models such as water balance models. The FAO56 PM method has been recommended as a standard approach to estimate the reference evapotranspiration with relatively high accuracy. However, the FAO56 PM method is often challenging to apply because it requires considerable hydrometeorological variables. In this perspective, the Hargreaves equation has been widely adopted to estimate the reference evapotranspiration. In this study, a set of parameters of the Hargreaves equation was calibrated with relatively long-term data within a Bayesian framework. Statistical index (CC, RMSE, IoA) is used to validate the model. RMSE for monthly results reduced from 7.94 ~ 24.91 mm/month to 7.94 ~ 24.91 mm/month for the validation period. The results confirmed that the accuracy was significantly improved compared to the existing Hargreaves equation. Further, the evaporative demand drought index (EDDI) based on the evaporative demand (E0) was proposed. To confirm the effectiveness of the EDDI, this study evaluated the estimated EDDI for the recent drought events from 2014 to 2015 and 2018, along with precipitation and SPI. As a result of the evaluation of the Han-river watershed in 2018, the weekly EDDI increased to more than 2 and it was confirmed that EDDI more effectively detects the onset of drought caused by heatwaves. EDDI can be used as a drought index, particularly for heatwave-driven flash drought monitoring and along with SPI.

수문기상인자 중 하나인 증발산은 수자원 계획 및 관리 시 고려되며, 특히 물수지모형 등 수문모형의 입력자료로 활용된다. FAO56 PM 방법은 기상인자로부터 기준증발산량(reference evapotranspiration, ET0)을 추정하며, 상대적으로 높은 정확성을 보여준다. 그러나 FAO56 PM 방법은 많은 기상인자가 필요하기 때문에 증발산 추정에 한계가 있다. 이러한 점에서 온도인자 기반의 Hargreaves 식의 매개변수를 Bayesian 모형을 통해 지역적으로 재추정하여 기준증발산량을 산정하였다. 통계 지표(CC, RMSE, IoA)를 활용하여 모형검증을 수행한 결과, 검증 기간에 대해 RMSE는 7.94 ~ 24.91 mm/month에서 6.77 ~ 12.94 mm/month로 기존 Hargreaves 식으로 추정된 증발산량에 비해 정확도가 크게 개선되었다. 본 연구에서는 산정된 기준증발산량을 활용해 증발 요구량(E0) 기반의 가뭄지수 EDDI (evaporative demand drought index)를 제시하였다. 가뭄지수로서 적용성을 확인하기 위해 강수량 및 SPI와 함께 최근 2014 ~ 2015년, 2018년 가뭄사상을 평가하였다. 한강유역에 위치한 춘천, 홍천의 2018년 가뭄 발생 당시, 주단위 EDDI가 2 이상까지 증가하였으며, 이를 통해 EDDI가 강수부족보다는 폭염에 대한 반응정도가 큰 것을 확인할 수 있었다. 가뭄지수 EDDI는 SPI와 함께 가뭄 분석 및 평가에 대해 활용성이 높은 것으로 사료된다.

Keywords

Acknowledgement

본 결과물은 환경부의 재원으로 한국환경산업기술원의 지능형 도시수자원 관리사업의 지원을 받아 연구되었습니다(2019002950001).

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