• Journal of Environmental Science International
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• v.19 no.3
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• pp.295-304
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• 2010

Actual evapotranspiration (AET) in the Suyeong-gu was estimated and correlations between AET and meteorological factors were analyzed. The study area was Suyeong-gu lay at the east longitude $129^{\circ}$ 05' 40" ~ 129$^{\circ}$ 08' 08" and north latitude $35^{\circ}$ 07' 59" ~ $35^{\circ}$ 11' 01". The Kumryun mountain, the Bae mountain, the Suyeong river and the Suyeong bay are located on west, north, northeaster and south side in the study area, respectively. AET was estimated using precipitation (P), potential evapotranspiration (PET) and plant-available water coefficient. Meteorological factors to estimate PET were air temperature, dewpoint temperature, atmospheric pressure, duration of sunshine and mean wind speed (MWS). PET and AET were estimated by a method of Allen et al. (1998) and Zhang et al. (2001), respectively. PET was the highest value (564.45 mm/yr) in 2002 year, while it was the lowest value (449.95 mm/yr) in 2003 year. AET was estimated highest value (554.14 mm/yr) in 2002 year and lowest value (427.91 mm/yr) in 2003 year. Variations of PET and AET were similar. The linear regression function of AET as PET using monthly data was AET=0.87$\times$PET+3.52 and coefficient of determination was high, 0.75. In order to analyze relationship between the evapotranspiration and meteorological factors, correlation analysis using monthly data were accomplished. Correlation coefficient of AET-PET was 0.96 high, but they of AET-P and PET-P were very low. Correlation coefficients of AET-MWS and PET-MWS were 0.67 and 0.73, respectively. Thus, correlation between evapotranspiration and MWS was the highest among meteorological factors in Suyong-gu. This means that meteorological factor to powerfully effect for the variation of evapotranspiration was MWS. The linear regression function of AET as MWS was AET=84.73$\times$MWS+223.05 and coefficient of determination was 0.54. The linear regression function of PET as MWS was PET=83.83$\times$MWS+203.62 and coefficient of determination was 0.45.

• Water Engineering Research
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• v.5 no.3
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• pp.123-131
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• 2004

This paper describes the use of spatial interpolation for estimating seasonal crop potential evapotranspiration (PET) and irrigation water requirement in unmeasured evaporation gage stations within Edwards Aquifer, Texas using GIS. The Edwards Aquifer area has insufficient data with short observed records and rare gage stations, then, the investigation of data for determining of irrigation water requirement is difficult. This research shows that spatial interpolation techniques can be used for creating more accurate PET data in unmeasured region, because PET data are important parameter to estimate irrigation water requirement. Recently, many researchers are investigating intensively these techniques based upon mathematical and statistical theories. Especially, three techniques have well been used: Inverse Distance Weighting (IDW), spline, and kriging (simple, ordinary and universal). In conclusion, the result of this study (Table 1) shows the kriging interpolation technique is found to be the best method for prediction of unmeasured PET in Edwards aquifer, Texas.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.674-678
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• 2011

The model to estimate potential evapotranspiration (PET) was developed using periodic function. Average PET during 30 years for 67 areas was $2.36mm\;day^{-1}$, and those were distributed with the range of $1.42{\sim}3.45mm\;day^{-1}$. The period of PET change was 16~32 years according to area.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.45 no.4
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• pp.241-244
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• 2000

This experiment was conducted to evaluate the effect on evapotranspiration and yield of soybean according to different soil water conditions, and to find the optimum time and amount for irrigation in soybean cultivation. The difference between potential evapotranspiration (PET) and maximum evapotranspiration (MET) during growing season of soybean planted in lysimeter was higher during reproductive stage than during vegetative one. The maximum crop coefficient was obtained at beginning seed stage of soybean. Soil water coefficient of irrigation treatment was higher than that of non-irrigation treatment during soybean growth stage in field experiment. Grain yield was highest in lysimeter due to its high water use efficiency and evapotranspiration rate.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.264-264
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• 2023

물순환 과정에서의 증발산은 장기적인 관점에서의 수자원 계획 수립 시 중요한 요소이다. 증발산은 기온, 상대습도, 일사량 등 기상학적 인자뿐만 아니라 증발표면, 식생분포 등 다양한 인자의 복합작용에 의해 일어나므로, 유역 단위에서 발생한 실제증발산(Actual evapotranspiration, AET)을 측정하기에는 기술적인 한계가 존재한다. 그러나 증발산 보완관계(Complementary relationship of evapotranspiration, CRE) 가설을 활용하면, 수문요소의 상호작용을 고려한 모델링을 거치지 않고도, 비교적 간단하게 AET를 추정할 수 있다. 본 연구는 증발산 관측자료를 기반으로 유역 단위에서의 CRE를 검증하고자 하며, 플럭스 타워 등 다양한 관측장비가 설치되어 있는 용담댐 시험유역을 대상유역으로 선정하였다. 용담댐 유역 내 산지에 위치한 덕유산 플럭스 타워에서 측정된 증발산을 AET로 보았으며, 유역 인근에 위치한 전주 기상관측소에서 측정되는 팬 증발량(E_pan)을 잠재증발산량(Potential evapotranspiration, PET)으로 보았다. E_pan 계측시, 증발팬의 가열 등 주변환경 변화로 인해 과다하게 추정되는 값을 보완하기 위해 FAO Penman-Monteith 식을 활용해 팬 증발량 보정계수(Coefficient of pan evaporation, k_p)를 산정하여 적용하였다. 습윤증발산량(Wet evapotranspiration, WET)은 대기가 완전히 포화되었을 때 발생하는 증발산량으로, 댐 수표면에서 계측되는 수면증발량을 WET로 보았다. CRE 검증을 위해 AET와 PET를 각각 WET로 나누어 AET+와 PET+로 무차원화하였으며, 습윤지수(Moisture Index, MI)는 AET를 PET로 나누어 산정하였다. CRE 가설은 MI에 따른 AET+와 PET+가 서로 보완관계를 갖는다는 것인데, 용담댐 유역의 관측자료를 활용하여 CRE를 검증한 결과 AET+와 PET+ 간의 비대칭계수(b)가 1.23인 것으로 나타났다. 이 때의 평균제곱오차(MSE)는 0.599, 결정계수(R₂)는 0.631로 나타나 CRE의 b가 적합하게 추정된 것으로 판단된다. 본 연구결과와 같이 검증된 CRE를 통해 증발산 관측지점이 없거나, 조밀하지 않은 유역의 AET를 간접추정할 수 있으며, 이를 활용해 보다 정확한 댐의 장기유출 모의와 용수공급계획 수립에 도움을 줄 수 있을 것으로 기대된다.

• Water Engineering Research
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• v.5 no.1
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• pp.1-16
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• 2004

The purpose of this study is to understand the characteristics of hourly PET(Potential Evapo Transpiration) variation estimated using Penman ET model. The estimated PET using Penman model was compared with measured ET. For this study, two subwatersheds were selected, and fluxes, meteorological data and soil moisture data were measured during the summer and winter days. During the winter days, the aerodynamic term of Penman ET is much greater than that of energy term of Penman ET for dry soil condition. The opposite phenomena appeared fer wet soil condition. During the summer days, energy term is much more important factor for ET estimation compared with aerodynamic term regardless of soil moisture condition. Penman ET, measured ET, and energy term show the similar hourly variation pattern mainly because the influence of net radiation on the estimation of Penman ET is much more significant compared with other variables. Even though there are much more soil moisture in the soil during the wet days, the estimated hourly ET from Penman model and measured hourly ET have smaller values compared with those of dry days, indicating the effect of cloudy weather condition.

• Korean Journal of Agricultural and Forest Meteorology
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• v.19 no.2
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• pp.62-72
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• 2017

Spatio-temporal projection of evapotranspiration over croplands would be useful for assessment of climate change impact and development of adaptation strategies in agriculture. Potential evapotranspiration (PET) and dryness index (DI) during rice growing seasons were calculated using climate change scenario data provided by the National Institute of Meteorological Research (NIMR). A data processing tool for gridded climate data files, readGrADSWrapper, was used to calculate PET and DI during the current (1986-2005) and future (2006-2100) periods. Scripts were written to implement the formulas of PET and DI in R, which is an open source statistical data analysis tool. Evapotranspiration in rice fields ($PET_{Rice}$) was also determined using R scripts. The Spatio-temporal patterns of PET differed by regions in Korean Peninsula under current and future climate conditions. Overall, PET and $PET_{Rice}$ tended to increase throughout the $21^{st}$ century. Those results suggested that region-specific water resource managements would be needed to minimize the risk of water loss in the regions where considerable increases in PET would occur under the future climate conditions. For example, a number of provinces classified as a humid region were projected to become a sub-humid region in the future. The Spatio-temporal assessment of water resources based on PET and DI would help the development of climate change adaptation strategies for rice production in the 21st century. In addition, the studies on climate change impact would be facilitated using specialized data tools, e.g., readGrADSWrapper, for geospatial analysis of climate data.

• Journal of Environmental Science International
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• v.5 no.5
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• pp.657-662
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• 1996

Meteorological and flux data measured from semiarid watersheds (Lucky Hills and Kendall) during the summer rainy and winter periods were used to study the sensitivity of the those variables used in the estimation of evapotranspiration rates. Relative sensitivity was examined to compare the importance of four meteorological and flux variables (net radiation wind speed, air temperature, and relative humidity) on Penman potential evapotranspiration (PET) estimation. The study results show that variations in Penman PET rates during the summer rainy period at both watersheds appears to be controlled by air temperature adn net radiation. During the winter period at both watersheds, wariations in Penman PET rates appears to be controlled by relative humidity and air temperature.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.3
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• pp.51-57
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• 1988

The purpose of this paper is to know the effect of Adjustment factor (C) in Penman equation In the modified Penman equation by Doorenbos and Pruitt (1977), Potential Evapotranspiration(PET) was calculated in cases of (1) neglecting Adjustment factor (C=1, 0, A), (2) fixing Day/Night wind ratio (URATIO) to 2.0(B-l) and computing daily URATIO (B-2), and was compared with Actual Evapotranspiration (AET) for paddy fields in Suwon (1985-1986). The followings are a summary of this study results ; 1. Using 1985-1986 meteorological data, daily average PET in cases of A, B-i, B-2 were 4.61 mm/day, 4.81 mm/day and 5.36 mm/day respectively and daily average AET was 4.26 mm/day. The increment ratios of PET based on case A were 100%, 104.34% and 116.27% 2. The range of Adjustment factor (C) in cases of B-i, B-2 were 0.916-1.140 and 0.922-1.392 respectively. 3. The regression coefficient(r) between AET and PET in cases of A, B-i, B-2 were 0.928, 0.924 and 0.915 respectively.

• Water for future
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• v.29 no.2
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• pp.235-247
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• 1996

Meteorological and soil water content data measured from semiarid watersheds of Lucky Hills and Kendall during the summer rainy and winter periods were used to study the interrelationships between the controlling variables of the evapotranspiration, and to evaluate the effects of variables on daily actual evapotranspiration (ET) estimation. Simple and multiple linear regression (MLR) analyses were employed to evaluate the order of importance of the meteorological and soil water factors involved. The information gained was used for MLR model development. Theavailable energy and vapor pressure deficit were found to be the important variables to estimate actual ET (AET) for both periods and at both watersheds. Therefore, the important variables of evapotranspiration process in these semiarid watersheds appear to be simply the components of energy term in available energy and aerodynamic term in vapor pressure deficit of Penman potential evapotranspiration (PET) equation.