Korean Journal of Agricultural and Forest Meteorology (한국농림기상학회지)

Korean Society of Agricultural and Forest Meteorology (한국농림기상학회)
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Calibration of Hargreaves Equation Coefficient for Estimating Reference Evapotranspiration in Korea

우리나라 기준증발산량 추정을 위한 Hargreaves 공식의 계수 보정

  • Hwang, Seon-ah (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Han, Kyung-hwa (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Zhang, Yong-seon (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Cho, Hee-rae (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Ok, Jung-hun (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Kim, Dong-Jin (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Kim, Gi-sun (Divison of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration) ;
  • Jung, Kang-ho (Division of Planning & Coordination, National Institute of Agricultural Sciences, Rural Development Administration)
  • 황선아 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 한경화 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 장용선 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 조희래 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 옥정훈 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 김동진 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 김기선 (농촌진흥청 국립농업과학원 토양비료과) ;
  • 정강호 (농촌진흥청 국립농업과학원 기획조정과)
  • Received : 2019.10.01
  • Accepted : 2019.11.13
  • Published : 2019.12.30
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Abstract

The evapotranspiration is estimated based on weather factors such as temperature, wind speed and humidity, and the Hargreaves equation is a simple equation for calculating evapotranspiration using temperature data. However, the Hargreaves equation tends to be underestimated in areas with wind speeds above 3 m s-1 and overestimated in areas with high relative humidity. The study was conducted to determine Hargreaves equation coefficient in 82 regions in Korea by comparing evapotranspiration determined by modified Hargreaves equation and the Penman-Monteith equation for the time period of 2008~2018. The modified Hargreaves coefficients for 50 inland areas were estimated to be 0.00173~0.00232(average 0.00196), which is similar to or lower than the default value 0.0023. On the other hand, there are 32 coastal areas, and the modified coefficients ranged from 0.00185 to 0.00303(average 0.00234). The east coastal area was estimated to be similar to or higher than the default value, while the west and south coastal areas showed large deviations by area. As results of estimating the evapotranspiration by the modified Hargreaves coefficient, root mean square error(RMSE) is reduced from 0.634~1.394(average 0.857) to 0.466~1.328(average 0.701), and Nash-Sutcliffe Coefficient(NSC) increased from -0.159~0.837(average 0.647) to -0.053~0.910(average 0.755) compared with original Hargreaves equation. Therefore, we confirmed that the Hargreaves equation can be overestimated or underestimated compared to the Penman-Monteith equation, and expected that it will be able to calculate the high accuracy evapotranspiration using the modified Hargreaves equation. This study will contribute to water resources planning, irrigation schedule, and environmental management.

기준증발산량은 기온, 풍속, 습도 등 기상요소를 바탕으로 추정하는 방법을 이용하고 있으며, Hargreaves 공식은 기온자료를 이용하여 기준증발산량을 산정할 수 있는 간단한 경험식이라 할 수 있다. 그러나 Hargreaves 공식은 풍속이 3 m s-1 이상인 지역에서는 과소평가 되고, 상대습도가 높은 지역은 과대평가 되는 경향이 있다. 본 연구에서는 Hargreaves 공식을 우리나라에 적용하기 위해 보다 정확한 기준증발산량 추정이 가능하도록 계수 산정 연구를 수행하였다. 우리나라 종관기상관측지점(ASOS, Automated Synoptic Observing System)의 최근 11 년(2008-2018) 동안의 기상자료를 이용하여 Panman-Monteith 공식으로 기준증발산량을 추정하였고, 이 값을 기준으로 하여 각 지점별로 Hargreaves 공식의 계수를 보정하였다. 우리나라 82 개 지점에 대하여 지역별로 보정된 계수는 내륙지역이 50 개 지점이며, 0.00173~0.00232(평균0.00196)로 기본값인 0.0023 과 비슷하거나 낮게 산정되었다. 반면, 해안지역은 32 개 지점이며 지역별로 보정된 계수의 범위는 0.00185~0.00303(평균 0.00234)으로 동해안지역은 기본값과 비슷하거나 높게 산정된 반면, 서해안과 남해안지역은 지역별로 편차가 크게 나타났다. Hargreaves 공식의 계수를 보정하여 기준증발산량을 추정한 결과 RMSE(Root Mean Square Error)는 계수 보정 전 0.634~1.394(평균 0.857)에서 계수 보정 후 0.466~1.328(평균 0.701)로 낮아지고, NSC(Nash-Sutcliffe Coefficient)는 계수 보정 전 -0.159~0.837(평균 0.647)에서 계수 보정 후 -0.053~0.910(평균 0.755)로 높아짐에 따라 기준증발산량의 추정효율이 크게 향상되는 것으로 나타났다. 연구 결과, Hargreaves 공식을 그대로 이용할 경우 Penman-Monteith 공식에 비해 과대 또는 과소 산정될 수 있음을 확인하였으며, 계수를 보정하여 이용할 경우 정확도가 높은 기준증발산량을 추정할 수 있을 것으로 판단된다.

Keywords

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