scholarly journals How Ångström–Prescott Coefficients Alter the Estimation of Agricultural Water Demand in South Korea

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1851
Author(s):  
Hanseok Jeong ◽  
Rabin Bhattarai ◽  
Syewoon Hwang ◽  
Jae-Gwon Son ◽  
Taeil Jang
Keyword(s):  
South Korea ◽  
Global Solar Radiation ◽  
Water Requirement ◽  
Agricultural Water ◽  
Reference Crop Evapotranspiration ◽  
Agricultural Water Management ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Reference Crop ◽  
Monteith Equation

The Food and Agriculture Organization (FAO) Penman–Monteith equation, recognized as the standard method for the estimation of reference crop evapotranspiration (ET0), requires many meteorological inputs. The Ångström–Prescott (A-P) formula containing parameters (i.e., a and b) is recommended to determine global solar radiation, one of the essential meteorological inputs, but may result in a considerable difference in ET0 estimation. This study explored the effects of A-P coefficients not only on the estimation of ET0, but also on the irrigation water requirement (IWR) and design water requirement (DWR) for paddy rice cultivation, which is the largest consumer of agricultural water in South Korea. We compared and analyzed the estimates of ET0, IWR, and DWR using the recommended (a = 0.25 and b = 0.5) and locally calibrated A-P coefficients in 16 locations of South Korea. The estimation of ET0 using the recommended A-P coefficients produced significant overestimation. The overestimation ranged from 3.8% to 14.0% across the 16 locations as compared to the estimates using the locally calibrated A-P coefficients, and the average overestimation was 10.0%. The overestimation of ET0 corresponded to a variation of 1.7% to 7.2% in the overestimation of the mean annual IWR, and the average overestimation of the IWR was 5.1%. On average, the overestimation was slightly reduced to 4.8% in DWR estimation, since the effect of A-P coefficients on the IWR estimation decreased as the IWR increased. This study demonstrates how the use of A-P coefficients can alter the estimation of ET0, IWR, and DWR in South Korea, which underscores the importance of their proper consideration in agricultural water management.

scholarly journals A Thermodynamically Based Model for Actual Evapotranspiration of an Extensive Grass Field Close to FAO Reference, Suitable for Remote Sensing Application

2016 ◽  
Vol 17 (5) ◽  
pp. 1373-1382 ◽  
Author(s):  
H. A. R. de Bruin ◽  
I. F. Trigo ◽  
F. C. Bosveld ◽  
J. F. Meirink
Keyword(s):  
Global Radiation ◽  
Actual Evapotranspiration ◽  
Net Radiation ◽  
Reference Crop Evapotranspiration ◽  
In Situ Data ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
A Site ◽  
Reference Crop

Abstract A thermodynamically based model is presented to estimate daily actual evapotranspiration (ET) of a grass site closely resembling reference grass as defined by the Food and Agriculture Organization of the United Nations (FAO) under nonadvective conditions, from Meteosat Second Generation (MSG) imagery. The model presented here is derived from the thermodynamic theory by Schmidt combined with an atmospheric boundary layer model. Daily net radiation over the (reference) grass surface is parameterized as a function of global radiation, which can be estimated from MSG observations. It is then shown that ET over the grass area can be estimated using remotely sensed daily global radiation and air temperature as input only. The validation relied on observations gathered in Cabauw, a site closely resembling the reference grass, as defined by the FAO. The comparison with in situ data indicated a bias of 2.8 W m−2 and an RMSE of 7.7 W m−2. The possibility of using the approach developed here to provide reference crop evapotranspiration ETo is discussed. Because of the ambiguousness of ETo definition regarding local advection effects, it should be noted that explicitly advection-free conditions are dealt with. It is pointed out that in semiarid regions local advection cannot be ignored.

scholarly journals Comparison of meteorological data, related to reference evapotranspiration, from conventional and automatic stations in the Sertão and Agreste regions of Pernambuco, Brazil

DYNA ◽  
2021 ◽  
Vol 88 (216) ◽  
pp. 176-183
Author(s):  
Iug Lopes ◽  
Miguel Julio Machado Guimarães ◽  
Juliana Maria Medrado de Melo ◽  
Ceres Duarte Guedes Cabral de Almeida ◽  
Breno Lopes ◽  
...  
Keyword(s):  
Reference Evapotranspiration ◽  
Meteorological Data ◽  
Global Solar Radiation ◽  
Concordance Index ◽  
Good Relationship ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Daily Scale ◽  
Weather Stations ◽  
Meteorological Elements

The objective was to perform a comparative study of the meteorological elements data that most cause changes in the reference Evapotranspiration (ETo, mm) and its own value, of automatic weather stations AWS and conventional weather stations CWS of the Sertão and Agreste regions of Pernambuco State. The ETo was calculated on a daily scale using the standard method proposed by the Food and Agriculture Organization (FAO), Penman-Monteith (FAO-56). The ETo information obtained from AWS data can be used to update the weather database of stations, since there is a good relationship between the ETo data obtained from CWS and AWS, statistically determined by the Willmott's concordance index (d > 0.7). The observed variations in the weather elements: air temperature, relative humidity, wind speed, and global solar radiation have not caused significant changes in the ETo calculation.

Study on Regional Analysis of Reference Crop Evapotranspiration Based on SPSS

2015 ◽  
Vol 733 ◽  
pp. 415-418
Author(s):  
Li Ying Cao ◽  
He Long Yu ◽  
Gui Fen Chen ◽  
Peng Sun
Keyword(s):  
Regression Analysis ◽  
Linear Regression ◽  
Linear Correlation ◽  
Meteorological Data ◽  
Linear Regression Analysis ◽  
Regional Analysis ◽  
Crop Evapotranspiration ◽  
Reference Crop Evapotranspiration ◽  
Reference Crop ◽  
Monteith Equation

Based on the meteorological data collected from 3 stations in recent 10 years in Fushun region, the reference crop evapotranspiration was calculated with the Penman-Monteith equation recommended by FAO in 1990. The evapotranspiration of the region was analyzed using linear regression analysis based on software of SPSS. The results showed that the linear correlation was evident between the evapotranspiration data of stations, but it is not significant for the linear correlation between the stations, neither between the stations. The result will be helpful to analysis of the space distributions of the reference crop evapotranspiration in the region.

scholarly journals Modification of FAO Penman–Monteith equation for minor components of energy

2018 ◽  
Vol 50 (2) ◽  
pp. 607-615
Author(s):  
Arman Varmaghani ◽  
William E. Eichinger ◽  
John H. Prueger
Keyword(s):  
Energy Equation ◽  
Minor Components ◽  
Net Radiation ◽  
Obukhov Length ◽  
Available Energy ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Monteith Equation ◽  
Energy Components

Abstract The conventional Food and Agriculture Organization of the United Nations (FAO) Penman–Monteith (P-M) equation requires knowledge of the available energy to estimate reference evapotranspiration (ETo); however, it is common to ignore the minor energy components (MECs). This study was conducted to determine the effect of not including the MECs in the FAO P-M equation. Fifteen-min micrometeorological records of four sites (covered with corn, soybeans, and prairie) in central Iowa, USA, during the years 2007–2012 were investigated. The major/minor components of the energy equation were either measured or estimated by in-situ eddy covariance instruments. It was discovered that, on average, the MECs accounted for at least 13% of daily net radiation, leading to 27% decrease in daily ETo. Therefore, an equation is introduced to estimate MECs as a function of net radiation, air temperature, and Monin–Obukhov length; and another equation is regressed to roughly estimate daily MECs as a function of net radiation and day of the year. The findings in this study suggest a fundamental modification of FAO P-M formula by considering the inclusion of MECs in the energy term.

scholarly journals Temporal Downscaling of Crop Coefficient and Crop Water Requirement from Growing Stage to Substage Scales

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Songhao Shang
Keyword(s):  
Water Management ◽  
Reference Evapotranspiration ◽  
Crop Coefficient ◽  
Water Requirement ◽  
Crop Water Requirement ◽  
Crop Evapotranspiration ◽  
Agricultural Water ◽  
Crop Water ◽  
Agricultural Water Management

Crop water requirement is essential for agricultural water management, which is usually available for crop growing stages. However, crop water requirement values of monthly or weekly scales are more useful for water management. A method was proposed to downscale crop coefficient and water requirement from growing stage to substage scales, which is based on the interpolation of accumulated crop and reference evapotranspiration calculated from their values in growing stages. The proposed method was compared with two straightforward methods, that is, direct interpolation of crop evapotranspiration and crop coefficient by assuming that stage average values occurred in the middle of the stage. These methods were tested with a simulated daily crop evapotranspiration series. Results indicate that the proposed method is more reliable, showing that the downscaled crop evapotranspiration series is very close to the simulated ones.

scholarly journals Lysimeter-Based Water Use and Crop Coefficient of Drip-Irrigated Potato in an Arid Environment

Agronomy ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 756 ◽  
Author(s):  
Alataway ◽  
Al-Ghobari ◽  
Mohammad ◽  
Dewidar
Keyword(s):  
Water Use ◽  
Irrigation Schedule ◽  
Crop Coefficient ◽  
Arid Environment ◽  
Crop Evapotranspiration ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Use Efficiency ◽  
Monteith Equation

The determination of the water requirements and crop coefficient (Kc) of agricultural crops helps to create an appropriate irrigation schedule, and with the effective management of irrigation water. The aim of this research was to estimate the water requirement, Kc, and water-use efficiency (WUE) of potato using non-weighing-type lysimeters in four regions of the Kingdom of Saudi Arabia (Qassiem, Riyadh, Al-Jouf, and Eastern). Our results clearly show that the accumulated values of the measured crop evapotranspiration of potato derived from the lysimeters were 573, 554, 592, and 570 mm, while the accumulated values of the predicted crop evapotranspiration from Penman-Monteith equation based on FAO (Food and Agriculture Organization) were 651, 632, 672, and 647 mm for the Qassiem, Riyadh, Al-Jouf, and Eastern regions, respectively. The Kc values of potato obtained from the lysimeters were Kc initial (0.58, 0.54, 0.50, and 0.52), Kc middle (1.02, 1.05, 1.13, and 1.10), and Kc end (0.73, 0.74, 0.74, and 0.75) for the Qassiem, Riyadh, Al-Jouf, and Eastern regions, respectively. Based on the amount of water used and the yield achieved, the highest WUE (3.6 kg m−3) was observed in the Riyadh region, while the lowest WUE (1.5 kg m−3) was observed in the Al-Jouf region.

scholarly journals Estimation methods of reference evapotranspiration (ETo) for Uberlândia -MG

2015 ◽  
Vol 35 (1) ◽  
pp. 27-38 ◽  
Author(s):  
ZILDA C. DE LACERDA ◽  
JOSÉ E. P. TURCO
Keyword(s):  
Solar Radiation ◽  
Reference Evapotranspiration ◽  
Global Solar Radiation ◽  
Daily Basis ◽  
Meteorological Station ◽  
Estimation Methods ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Daily Data ◽  
Analysis Of Results

One approach to verify the adequacy of estimation methods of reference evapotranspiration is the comparison with the Penman-Monteith method, recommended by the United Nations of Food and Agriculture Organization - FAO, as the standard method for estimating ET0. This study aimed to compare methods for estimating ET0, Makkink (MK), Hargreaves (HG) and Solar Radiation (RS), with Penman-Monteith (PM). For this purpose, we used daily data of global solar radiation, air temperature, relative humidity and wind speed for the year 2010, obtained through the automatic meteorological station, with latitude 18° 91' 66" S, longitude 48° 25' 05" W and altitude of 869m, at the National Institute of Meteorology situated in the Campus of Federal University of Uberlandia - MG, Brazil. Analysis of results for the period were carried out in daily basis, using regression analysis and considering the linear model y = ax, where the dependent variable was the method of Penman-Monteith and the independent, the estimation of ET0 by evaluated methods. Methodology was used to check the influence of standard deviation of daily ET0 in comparison of methods. The evaluation indicated that methods of Solar Radiation and Penman-Monteith cannot be compared, yet the method of Hargreaves indicates the most efficient adjustment to estimate ETo.

scholarly journals Evaluation of Potential Evapotranspiration Based on CMADS Reanalysis Dataset over China

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1126 ◽  
Author(s):  
Ye Tian ◽  
Kejun Zhang ◽  
Yue-Ping Xu ◽  
Xichao Gao ◽  
Jie Wang
Keyword(s):  
Wind Speed ◽  
Solar Radiation ◽  
Potential Evapotranspiration ◽  
Swat Model ◽  
Western China ◽  
Reanalysis Dataset ◽  
The North ◽  
Food And Agriculture ◽  
Food And Agriculture Organization ◽  
Monteith Equation

Potential evapotranspiration (PET) is used in many hydrological models to estimate actual evapotranspiration. The calculation of PET by the Food and Agriculture Organization of the United Nations (FAO) Penman–Monteith method requires data for several meteorological variables that are often unavailable in remote areas. The China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) reanalysis datasets provide an alternative to the use of observed data. This study evaluates the use of CMADS reanalysis datasets in estimating PET across China by the Penman–Monteith equation. PET estimates from CMADS data (PET_cma) during the period 2008–2016 were compared with those from observed data (PET_obs) from 836 weather stations in China. Results show that despite PET_cma overestimating average annual PET and average seasonal in some areas (in comparison to PET_obs), PET_cma well matches PET_obs overall. Overestimation of average annual PET occurs mainly for western inland China. There are more meteorological stations in southeastern China for which PET_cma is a large overestimate, with percentage bias ranging from 15% to 25% for spring but a larger overestimate in the south and underestimate in the north for the winter. Wind speed and solar radiation are the climate variables that contribute most to the error in PET_cma. Wind speed causes PET to be underestimated with percentage bias in the range −15% to −5% for central and western China whereas solar radiation causes PET to be overestimated with percentage bias in the range 15% to 30%. The underestimation of PET due to wind speed is offset by the overestimation due to solar radiation, resulting in a lower overestimation overall.

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