• 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.

• Journal of Korea Water Resources Association
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• v.53 no.11
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• pp.939-949
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• 2020

Currently, the demand for farmland is steadily decreasing due to changes in the agricultural environment and dietary life. In line with this, the government adopted an integrated water management with the enactment of the Framework Act on Water Management on June 2019. Therefore, it is required to take a closer look at agricultural water demand that accounts for 61% of water use for efficient water resources management. In this study, the overal process was evaluated for estimating agricultural water demand. More specifically, agricultural water demand for paddy field, which comprises 67% to 87% of agricultural water demand, was reviewed in detail. The biggest issue in estimating the paddy field water demand is the selection of the method for potential evapotranspiration. FAO recommends Penman-Monteith, but, currently, our criteria suggest a modified Penman equation that shows over estimation. Also, the crop coefficient, which is the main factor in evaluating evapotranspiration, has an issue that does not consider the current climate and crop varieties because it was developed 23 years ago. Comparing the Modified Penman and Penman-Monteith equations using the data from Jeonju National Weather Service, the modified Penman equation showed a big difference compared to the Penman-Monteith equation. When the crop coefficient was applied, the difference between late May and late August increased, where the amount of evapotranspiration was high. The estimation process was applied to four study reservoirs in Gimje. Comparing the estimated water demand with the supplied water record from reservoirs, the results showed that the estimation accuracy depends on not just the potential evapotranspiration, but also the standard water storing level in paddy fields.

• 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.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.233-242
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• 2010

SEBAL (Surface Energy Balance Algorithm for Land) developed by Bastiaanssen (1995) is an image-processing model comprisedof twenty-five sub models that calculates spatial evapotranspiration (ET) and other energy exchanges at the surface. SEBAL uses image data from Landsat or other satellites measuring thermal infrared radiation, visible and near infrared. In this study, the model was applied to Gyeongancheon watershed, the main tributary of Han river Basin. ET was computed on apixel-by-pixel basis from an energy balance using 4 years (2001-2004) Landsat and MODIS images. The scale effect between Landsat (30 m) and MODIS (1 km) was evaluated. The results both from Landsat and MODIS were compared with FAO Penman-Monteith ET. The absolute errors between satellite ETs and Penman-Monteith ET were within 12%. The spatial and temporal characteristics of ET distribution within the watershed were also analyzed.

• Journal of Korean Society of Forest Science
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• v.88 no.1
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• pp.86-92
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• 1999

Evapotranspiration is one of important variables affecting ecosystem processes such as vegetation distribution and growth. It acts as a limiting factor for natural water resource management. The transpiration of vegetation is mainly determined by climatic factors. The lower slope of the study area was densely forested with Pinus densiflora S. et Z. of 8 m height, and the upper slope was covered with poorly grown Pinus densiflora S. et Z. and Quercus trees. The amount of evapotranspiration was estimated to 590.3 mm/yr by annual water budget method. The canopy resistance of Penman-Monteith model was determined as 99 s/m. Seasonal evapotranspiration can be estimated with the calculated evaporation and the canopy resistance. The amount of evapotranspiration peaked in May. That is considered from both the direct evaporation of intercepted rainfall and the transpiration of vegetation during the dry spring season.

• Journal of Korea Water Resources Association
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• v.40 no.7
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• pp.571-583
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• 2007

The effects of climatic changes owing to urbanization, geographical and topographical conditions on Penman-Monteith reference evapotranspiration, and energy and aerodynamic terms of Penman-Monteith reference evapotranspiration have been studied. In this study, 56 climatological stations including the Seoul metropolis in South Korea have been selected, and the area of study site was set at $314\;km^2$. The climatological station is centrally located In the study area with a 10 km radius. The geographical and topographical characteristics of these sites were examined using GIS analysis. Land use status of the study area was also examined to estimate the extent of urbanization. The study results indicated that the variation of reference evapotranspiration rate is closely related to urbanization in most climatological stations. The level of change in reference evapotranspiration was higher in areas with higher urbanization rates. The change in reference evapotranspiration appears to be caused by temperature rises following heat island phenomena due to urbanization, and by the decrease in humidity, wind speed and sunshine duration due to the Increase in residential areas in urban districts. Especially, the humidity decrease causes a significant decrease in evapotranspiration rate. The study results showed that climatic change due to urbanization and proximity to the coast had the greatest effect on reference evapotranspiration.

• Journal of Korea Water Resources Association
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• v.52 no.12
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• pp.1033-1046
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• 2019

To evaluate the utilization suitability of solar radiation models, estimated solar radiation from 13 solar radiation models were verified by comparing with measured solar radiation at 5 study stations in South Korea. Furthermore, for the evaluation of evaporation estimates according to solar radiation models, 5 different evaporation estimation equations based on Penman's combination approach were applied, and evaporation estimates were compared with pan evaporation. Some solar radiation models require only meteorological data; however, some other models require not only meteorological data but also geographical data such as elevation. The study results showed that solar radiation model based on the ratio of the duration of sunshine to the possible duration of sunshine, maximum temperature, and minimum temperature provided the estimated solar radiation that most closely match measured solar radiation. Accuracy of estimated solar radiation also greatly improved when Angstrőm-Prescott model coefficients are adjusted to the study stations. Therefore, when choosing the solar radiation model for evaporation estimation, both data availability and model capability should be considered simultaneously. When applying measured solar radiation for estimating evaporation, evaporation estimates from Penman, FAO Penman-Monteith, and KNF equations are most close to pan evaporation rates in Jeonju and Jeju, Seoul and Mokpo, and Daejeon respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.47-51
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• 2009

증발산량을 산정하는 것은 자연현상과 인문현상을 이해하는 것의 기초가 된다. 이에, 최근 증발산량을 추정하는 많은 연구가 진행되고 있는 가운데 원격탐사 기법을 이용하는 것이 효과적인 것으로 알려지고 있다. 본 연구에서 소개할 SEBAL (Surface Energy Balance Algorithm for Land) (Bastiaanssen, 1995) 모형은 Landsat이나 NOAA 또는 MODIS 같은 원격탐사 위성으로부터 획득한 디지털 이미지 데이터(위성영상)를 이용하여, 지표에서 일어나는 증발산과 기타의 에너지 교환을 계산하는 이미지-프로세싱 모델이다. 우리나라 대상 유역에 위성영상을 사용하여 증발산량을 추정하는 SEBAL 모형의 적용 가능성을 검토하여, 유역 내 증발산량 분포의 시공간적 특성을 분석하고자 하였다. 연구 대상 지역은 유역 면적 약 6661.1km2의 충주댐 유역으로, Terra MODIS 위성영상을 이용하였다. SEBAL 증발산량의 평가를 위해 Penman-Monteith 공식에 의해 계산된 증발산량을 이용하여 비교하였으며, 그 결과 오차가 허용 가능한 10% 이내로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.35-39
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• 2011

토양과 식물의 잎에서 일어나는 증발산은 주로 증발접시, 침루계 등을 이용하여 실측하거나 에디 공분산, Bowen 비 등을 이용하여 경험적으로 측정할 수 있으나, 이러한 지점별 실측 자료는 공간적인 변동성이 큰 수문기상인자 특성상 지역적인 대표값으로 적용하는 데 어려움이 따른다. 본 연구에서는 이러한 기존 증발산 관측 방법의 단점을 보완하고자 인공위성 영상자료를 기반으로 한 원격탐사 기법을 이용하여 Penman-Monteith (PM)와 Priestley-Taylor (PT) 공간 증발산 산정 모형을 적용, 우리나라 증발산의 시공간적인 분포를 산정하였다. Terra 인공위성에 탑재된 Moderate Resolution Imaging Spectroradiometer (MODIS)로부터 제공되는 위성 영상 자료를 이용하여 기존에 연구된 증발산 모형을 이용하여 증발산을 산정하고 이를 상호 비교함으로써 우리나라에 대한 적용성을 검토하였다. 본 연구의 결과는 토양 및 식생이 소비하는 물의 양을 보다 정확하게 시공간적으로 파악하여 정부 차원의 수자원 관리 계획 수립에 유용하게 이용될 것이다.