• Journal of Korea Water Resources Association
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• v.37 no.6
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• pp.479-485
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• 2004

This study presents the calculation of evapotranspiration using estimated daily incoming solar radiation based on maximum daily temperature and minimum daily temperature. The Thornton and Running method(1999) was used to estimate daily incoming solar radiation and then the resulting solar radiation was compared with the measurements. It showed that the estimated daily solar radiation was within reasonable accuracy. In turn, the estimated daily solar radiation was applied to calculate the daily evapotranspiration using the Priestly-Taylor equation and Penman equation and the general results were that evapotranspiration was overestimated in the Priestly-Taylor equation but that Penman was a good estimator with this approach. It is encouraging that it is possible to use this approach, because the required historical data for its estimation are not extensively available and it is not easy to access the meteorological stations in most areas. The calculated eyapotranspiration was compared with that of Hargreaves which was based on daily temperature, and gives us some intuition in terms of engineering.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.125-125
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• 2019

현재 국내 논벼 수요량 산정방법은 수정 Penman방식에 의한 증발산량을 계산하여 구하고 있다. 증발산량 산정은 여러 가지 방식에 의해 산정될 수 있으나, 유엔의 식량농업기구 (FAO, Food and Agriculture Organization of the United Nations)에서는 작물 수요량 산정에 수정 Penman 공식을 사용할 경우 증발산량이 과다산정 되는 점을 지적하여, 건조 및 습윤 기후에서 비교적 정확하고 일정한 경향을 나타내는 Penman-Monteith(P-M)공식을 사용하도록 추천하였다. 이에 따라 국내 기상청 및 농촌진흥청에서도 증발산량 산정에 P-M공식을 적용하기 시작했으며, 이와 더불어 농촌진흥청에서는 P-M 추정법에 따른 벼를 포함한 주요 작물의 생육단계별 작물계수(Kc)를 제안하였다. 따라서 본 연구에서는 논용수 공급지구 8곳을 선정하여 대상지구별로 기존의 수정 Penman 방식과 P-M 방식을 적용한 경우의 증발산량 차이와 이에 따른 논벼 수요량 변화를 분석해 보았다. 그 결과, 수정 Penman 공식을 적용한 경우에 비해 P-M공식을 적용한 경우 증발산량이 모두 감소하는 경향을 나타내었다. 증발산량 산정방법 변화에 따른 대상지구별로 증발산량 결과값의 변화는 모두 비슷하게 나타났다. P-M방식을 적용했을 경우 잠재증발산량은 11.1%~14.9%(평균 12%)로 감소하였으며, 작물계수를 적용한 실제증발산량의 경우에도 3.8~5.1%(평균 4.6%) 감소하는 경향을 보였다. 이에 따른 논벼 수요량의 변화도 실제증발산량의 변화와 비슷한 감소 경향을 보였다. 다음으로 P-M방식을 채택한 경우의 논벼 수요량의 생육시기별 변화를 조사해 본 결과, 이앙기 수요량은 2.1%~6.3% (평균 4.4%)로 증가하다가, 본답기에는 수요량이 5.1%~11.3%(평균 8.4%)로 감소하였다. 전반적인 증발산량은 본답기 수요량 감소분이 이앙기 수요량 증가분보다 더 크기 때문에 감소경향을 나타낸 것으로 파악되었다. 또한 이앙기 수요량과 본답기 수요량의 증감의 경향이 다르게 나타난 것은 증발산량 산정방식의 변화에 따른 생육시기별 작물계수의 차이로 인한 변화로 파악되었다. 논벼 수요량은 농업용수 공급계획 수립의 주요기준이 되는 인자이므로, P-M방식 적용에 따른 논벼 수요량의 산정결과에 대해 보다 면밀한 검토가 필요할 것으로 사료된다.

• Journal of Korea Water Resources Association
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• v.50 no.12
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• pp.863-875
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• 2017

In this study, the effects of potential evapotranspiration method on drought index results were evaluated using SC-PDSI. Monthly heat index method, Penman-Monteith method, and Hargreaves equation were used as potential evapotranspiration method. SC-PDSI was calculated using three potential evapotranspiration method at 56 stations and compared the results. As a result, it was confirmed that the results by Penman-Monteith method and Hargreaves equation showed similar SC-PDSI calculation results without much difference, and the result by monthly heat index method showed a relatively large difference. It was confirmed that the results of SC-PDSI and drought situation judgment for the period of spring and winter season showed a big difference by the month. In conclusion, when calculating PDSI in Korea, using Penman-Monteith method and Hargreaves equation will be able to express the drought situation well.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.1
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• pp.13-23
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• 2006

In 1998, Food and Agriculture Organization addressed that FAO Modified Penman method possibly over-estimates consumptive use of water comparing to the measured reference crop evapotranspiration (PET) and Penman-Monteith method can be better choice for accurate PET estimation. Nevertheless it is still difficult to find research efforts about paddy rice crop coefficient for Penman-Monteith method. This study aims to estimate paddy rice crop coefficients for Penman-Monteith and FAO modified Penman methods in the manner of comparing two equations. To estimate the crop coefficients, measured evapotranspiration data during 1982-1986 and 1995-1997 were used. The average Penman-Monteith crop coefficients ranged from 0.78 to 1.58 for translated paddy rice and from 0.87 to 1.74 for flood-direct seeded paddy rice. The average FAO Modified Penman crop coefficients ranged from 0.65 to 1.35 for translated paddy rice and from 0.70 to 1.58 for flood-direct seeded paddy rice.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6B
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• pp.675-681
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• 2008

In this study, the daily-based reference evapotranspiration was evaluated with Hargreaves equation at the 23 meteorological stations for the time period of 1997-2006. The Hargreaves coefficient was self-calibrated to give the best fit with Penman-Monteith evapotranspiration, being regarded as a reference. On the basis of the estimated parameter set, a generalized regression was conducted to estimate the Hargreaves evapotranspiration by just using temperature data. This study will contribute to water resources planning, irrigation schedule, and environmental management.

• Journal of Korea Water Resources Association
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• v.41 no.4
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• pp.413-422
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• 2008

It is essential to locally adjust the Hargreaves parameter for estimating reference evapotranspiration with short data as a substitute of Penman-Monteith equation. In this study, evaluation of daily-based reference evapotranspiration is computed with Hargreaves equation. in Gyeonggi bay area including Ganghwa, Incheon, Suwon, Seosan, and Cheonan station for the time period of 1997-2004. Hargreaves coefficient is adjusted to give the best fit with Penman-Monteith evapotranspiration, being regarded as a reference. Then, the preferred parameters are validated for the same stations for the time period of 2005-2006. The optimization-based correction in calibration for 1997-2004 shows improved performance of the Hargreaves equation, giving 0.68-0.77 to 0.92-0.98 in Nash-Sutcliffe coefficient of efficiency (NSC) and 14.63-23.30 to 5.23-11.75 in RMSE. The validation for 2005-2006 shows improved performance of the Hargreaves equation, giving 0.43-0.85 to 0.93-0.97 in NSC and 14.43-26.81 to 6.48-9.09 in RMSE.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.20-25
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• 2005

In 1998, Food and Agriculture Organization addressed that FAO Modified Penman method possibly overestimates consumptive use of water comparing to the measured reference crop evapotranspiration (PET) and Penman-Monteith method can be better choice for accurate PET estimation. Nevertheless it is still difficult to find research efforts about paddy rice crop coefficient for Penman-Monteith method. This study aims to estimate paddy rice crop coefficients for Penman-Monteith method. To estimate the crop coefficients, measured evapotranspiration data during 1982-1986 were used. The average Penman-Monteith crop coefficients for transplanted paddy rice were ranged in $0.78\;{\sim}\;1.58$.

• Journal of Korea Water Resources Association
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• v.46 no.9
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• pp.933-946
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• 2013

The quantitative analysis of evapotranspiration (ET) is a key component in hydrological studies and the establishment of water resources planning. Generally, the quantitative analysis of ET is performed by the estimation method of potential or reference ET based on meteorological factors such as air temperature, wind speed, etc. Hargreaves equation is one of empirical methods for reference ET using air temperature data. In this study, in order to estimate more exact reference ET considering climatological characteristics in Korea, parameter regionalization of Hargreaves equation is carried out. Firstly, modified Hargreaves equation is presented after the analysis of the relationship between solar radiation and temperature. Secondly, parameter ($K_{ET}$) optimization of Hargreaves equation is performed using Penman-Monteith method and modified equation at 71 weather stations. Lastly, the equation for calculating $K_{ET}$ using temperature data is proposed and verified. As a result, reference ET from original Hargreaves equation is overestimated or underestimated compared with Penman-Monteith method. But modified equation in this study is more accurate in the climatic conditions of Korea. In addition, the applicability of the equation between $K_{ET}$ and temperature is confirmed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.495-504
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• 2008

Evapotranspiration (ET) is an important state variable while simulating daily streamflow in hydrological models. In the estimation of ET, for example, when using FAO Penman Monteith equation, the LAI (Leaf Area Index) value reflecting the conditions of vegetation generally affects considerably. Recently in evaluating the vegetation condition as a fixed quantity, the remotely sensed LAI from MODIS satellite data is available, and the time series values of spatial LAI coupled with land use classes are utilized for ET evaluation. Four years (2001-2004) of MODIS LAI was prepared for the evaluation of Penman Monteith ET in the continuous hydrological model, SLURP (Semi-distributed Land Use-based Runoff Processes). The model was applied for simulating the dam inflow of Chungju watershed ($6661.3km^2$) located in the upstream of Han river basin. For four years (2001-2004) dam inflow data and meteorological data, the model was calibrated and verified using MODIS LAI data. The average Nash-Sutcliffe model efficiency was 0.66. The 4 years watershed average Penman Monteith ETs of deciduous, coniferous, and mixed forest were 639.1, 422.4, and 631.6 mm for average MODIS LAI values of 3.64, 3.50, and 3.63 respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.341-341
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• 2019

물 순환과정의 구성요소 중 증발산(Evapotranspiration)은 수자원개발을 위한 계획의 수립과 수자원 시스템 운영적 측면에서 대단히 중요한 부분이다. 증발산량을 산정하기 위해서는 온도, 바람, 상대습도, 대기압, 수질 및 수표면의 성질과 형상 등을 산정하여야 하는데 이러한 기상자료들을 확보하기란 매우 어려운 실정이다. 본 연구에서는 기온자료만을 이용하여 기준증발산량을 산정할 수 있는 Hargreaves 공식의 경험적 매개변수 및 온도 매개변수를 수정하여 경안천유역의 기준증발산량을 산정하였다. 수정된 공식의 성능평가를 위해 현재 널리 사용되고 있는 Penman-Monteith 방법을 이용하여 산정된 기준증발산량을 정해로 가정하여 Root Mean Square Error와 Nash Sutcliffe Model Efficiency Coefficient분석을 수행하여 검증하였다. 또한 기온 및 Hargreaves 경험적 매개변수와의 상관관계를 이용한 회귀식에 대한 검증을 수행함으로써 본 연구에서 제안한 수정된 공식의 적용가능성을 확인하였으며, 향후 수자원 시스템 운영 측면에 도움이 될 것으로 판단된다.