scholarly journals Evapotranspiration and crop coefficients of melon plants measured by lysimeter and estimated according to FAO 56 methodology

2013 ◽  
Vol 33 (5) ◽  
pp. 929-939 ◽  
Author(s):  
Talyana K. de Melo ◽  
José F. de Medeiros ◽  
José E. Sobrinho ◽  
Vladimir B. Figueiredo ◽  
Paulo S. de Souza
Keyword(s):  
Reference Evapotranspiration ◽  
Irrigation Management ◽  
Climatic Conditions ◽  
Climatic Data ◽  
And Performance ◽  
Crop Coefficients ◽  
The City ◽  
Adequate Management ◽  
Monteith Equation ◽  
Statistical Indicators

Aiming at contributing to an adequate management of water resources, this study aimed to analyze and compare evapotranspiration (ETc) and crop coefficients (Kc) of melon plants measured by a lysimeter and estimated according to the FAO 56 methodology, in the city of Mossoró, state of Rio Grande do Norte (RN), Brazil. In order to measure ETc, weighing lysimeters with an area of 2.25m² were used, with two repetitions. The Penman-Monteith equation parameterized by FAO was used to estimate the reference evapotranspiration, and crop coefficients were those recommended in FAO-56 Bulletin adjusted to local climatic conditions. The required climatic data and lysimeter measurements were collected by an automatic weather station installed at the site. The results were compared by means of statistical indicators: of precision (r), of accuracy (d), and performance (c), in daily and weekly intervals. The data estimated by the FAO 56 methodology were adjusted optimally to the values measured by the lysimeters in accordance with index "c" in the two time scales assessed, indicating the potential of the method proposed by FAO to irrigation management in the climatic conditions of Agripole Assú-Mossoró.

Comparison between forecasts of reference evapotranspiration and ETo values calculated using data from different climatic conditions

2020 ◽  
Author(s):  
Ghaieth Ben Hamouda ◽  
Francesca Ventura ◽  
Daniele Zaccaria ◽  
Khaled M. Bali ◽  
Richard L. Snyder
Keyword(s):  
Reference Evapotranspiration ◽  
Irrigation Management ◽  
Climatic Conditions ◽  
Physical Models ◽  
Dew Point ◽  
Water Losses ◽  
Plant Canopies ◽  
Crucial Component ◽  
And Performance ◽  
Using Data

<p>Evapotranspiration is the transfer of water from the earth's surface to the atmosphere. It comprises the sum of water losses to atmosphere due to the processes of evaporation of moisture from soil, water bodies and wet plant canopies, and the transpiration of water from plants. Forecasts of this crucial component of the hydrologic cycle can be very valuable for growers, farm managers, irrigation practitioners, water resource planners and managers, and reservoir operators for their planning, allocation, delivery and scheduling decisions, as well as to hydrologic scientists for research purposes. Verifying the reliability of models’ forecasts is among the critical tasks for development and performance evaluation of physical models. In fact, the verification allows understanding the models’ behavior, and evaluating their applicability and dependability. The US National Weather Service (NWS) has released a product that provides forecasts of reference evapotranspiration (FRET) at 2.5-km grid resolution for the entire continental US. In this study, a comparison is made between ETo estimates from FRET and ETo values calculated by the California Irrigation Management Information System (CIMIS) for 68 days during summer 2019. Both the FRET forecasts and ETo values were obtained from NWS and CIMIS, respectively, on the basis of 15 CIMIS locations that are representative of different climatic conditions in California. In addition, air temperature, dew point temperature, relative humidity, wind speed, and vapor pressure deficit (VPD) data were also collected/calculated from the NWS and CIMIS websites to analyze the sensitivity of FRET forecasts to predictions of these parameters. All FRET forecasts were performed with timescales of 1, 3, 5 and 7 days. Statistical indices were calculated to assess the dependability of FRET values. They showed a good correlation of the FRET model outputs with CIMIS ETo data, with some differences depending on the climatic characteristics of selected weather stations’ locations, suggesting that FRET data could be valuable for anticipating near-future water demand and improve irrigation management in California.</p>

scholarly journals COMPARAÇÃO ENTRE MÉTODOS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA O MUNICÍPIO DE PETROLINA, PE

Irriga ◽  
2017 ◽  
Vol 1 (1) ◽  
pp. 31-39 ◽  
Author(s):  
Roberta Daniela Silva Santos ◽  
Marcello Henryque Costa de Souza ◽  
Regiane De Carvalho Bispo ◽  
Kevim Muniz Ventura ◽  
Luis Henrique Bassoi
Keyword(s):  
Reference Evapotranspiration ◽  
Estimation Method ◽  
Arid Climate ◽  
Estimation Methods ◽  
Coefficient Of Determination ◽  
Climatic Data ◽  
Test Field ◽  
Rating Method ◽  
And Performance ◽  
Semi Arid

COMPARAÇÃO ENTRE MÉTODOS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA O MUNICÍPIO DE PETROLINA, PE  ROBERTA DANIELA DA SILVA SANTOS1; MARCELLO HENRYQUE COSTA DE SOUZA1; REGIANE DE CARVALHO BISPO1; KEVIM MUNIZ VENTURA1 E LUÍS HENRIQUE BASSOI2 1Programa de Pós-Graduação em Irrigação e Drenagem, Universidade Estadual Paulista “Júlio de Mesquita Filho”- UNESP/FCA, Rua Dr. José Barbosa de Barros, 1780, Botucatu, SP, [email protected], [email protected], [email protected], [email protected] Embrapa Instrumentação, São Carlos, SP, [email protected]  1 RESUMO O conhecimento da evapotranspiração é vital na determinação das necessidades hídricas de uma cultura. Diante disso, o objetivo deste trabalho foi comparar o desempenho de sete métodos de estimativa da evapotranspiração de referência em relação ao método de Penman-Monteith, adotado como padrão, para o município de Petrolina, PE. Foram utilizados dados climáticos diários de 2004 a 2015, para estimar da ET0, obtidos na estação meteorológica automática do Campo Experimental de Bebedouro da Embrapa Semiárido, Petrolina, PE. Os indicadores estatísticos utilizados na avaliação foram: coeficiente de determinação (r²); coeficiente de correlação (r); índice de concordância (d) e índice de desempenho (c). Os valores do r² mostraram que o método de estimativa que melhor se ajustou ao método de Penman-Monteith foi o de Ivanov (0,73); seguido pelos métodos de Jensen-Haise (0,64); Makkink e Priestley-Taylor (0,63); Villa Nova (0,62); Hargreaves e Samani (0,53) e Hamon (0,45). No entanto, com relação ao do índice “c”, Hamon foi classificado com “péssimo”; Makkink como “mau”; Hargreaves e Samani e Villa Nova como “sofrível”; Ivanov e Priestley-Taylor como “mediano”; e Jensen-Haise como “bom”. Esse último método foi considerado como o de melhor classificação de desempenho. Palavras-chave: Penman-Monteith, correlação, semiárido.  SANTOS, R. D. S.; SOUZA, M. H. C.; BISPO, R. de C.; VENTURA, K. M.; BASSOI, L. H.METHOD-COMPARISON STUDY TO ESTIMATE THE REFERENCE EVAPOTRANSPIRATION IN PETROLINA, PE  2 ABSTRACT The knowledge on evapotranspiration is vital in determining the water requirements of a crop. Therefore, this paper aims to compare the performance of seven of estimation methods for the reference evapotranspiration in relation to the Penman-Monteith method, adopted as standard, for the municipality of Petrolina, state of Pernambuco, Brazil. We used daily climatic data from 2004 to 2015 to estimate the ET0 coefficient, obtained in the automatic weather station of the Test Field in Bebedouro, Embrapa in the Semi-arid climate. The statistical indicators used in the evaluation were: coefficient of determination (r²), correlation coefficient (r), agreement index (d) and performance index (c). The r2 values showed that the estimation method that best fitted to the Penman-Monteith method was Ivanov's (0.73), followed by Jensen-Haise (0.64), Makkink and Priestley-Taylor (0.63), Villa Nova (0.62), Hargreaves and Samani (0.53) and Hamon (0.45) methods. However, in relation to the index "c", Hamon was classified as "very poor"; Makkink as "poor"; Hargreaves and Samani and Villa Nova as "tolerable"; Ivanov and Priestley-Taylor as "medium"; and Jensen-Haise as "good". The last one was considered as the best performance rating method. Keywords: Penman-Monteith, correlation, semi-arid climate.

scholarly journals Performance of methods for estimation of table beet water requirement in Alagoas

2018 ◽  
Vol 22 (3) ◽  
pp. 189-193 ◽  
Author(s):  
Daniella P. dos Santos ◽  
Célia S. dos Santos ◽  
Leiliane M. da Silva ◽  
Márcio A. L. dos Santos ◽  
Cícero G. dos Santos
Keyword(s):  
Water Use ◽  
Standard Method ◽  
Water Scarcity ◽  
Performance Index ◽  
Reference Evapotranspiration ◽  
Irrigation Management ◽  
Crop Evapotranspiration ◽  
Abstract Optimization ◽  
Crop Coefficients ◽  
Drainage Lysimeter

ABSTRACT Optimization of water use in agriculture is fundamental, particularly in regions where water scarcity is intense, requiring the adoption of technologies that promote increased irrigation efficiency. The objective of this study was to evaluate evapotranspiration models and to estimate the crop coefficients of beet grown in a drainage lysimeter in the Agreste region of Alagoas. The experiment was conducted at the Campus of the Federal University of Alagoas - UFAL, in the municipality of Arapiraca, AL, between March and April 2014. Crop evapotranspiration (ETc) was estimated in drainage lysimeters and reference evapotranspiration (ETo) by Penman-Monteith-FAO 56 and Hargreaves-Samani methods. The Hargreaves-Samani method presented a good performance index for ETo estimation compared with the Penman-Monteith-FAO method, indicating that it is adequate for the study area. Beet ETc showed a cumulative demand of 202.11 mm for a cumulative reference evapotranspiration of 152.00 mm. Kc values determined using the Penman-Monteith-FAO 56 and Hargreaves-Samani methods were overestimated, in comparison to the Kc values of the FAO-56 standard method. With the obtained results, it is possible to correct the equations of the methods for the region, allowing for adequate irrigation management.

scholarly journals ESTUDO COMPARATIVO ENTRE METODOLOGIAS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA LOCALIDADES DO NORTE DE MINAS GERAIS

Irriga ◽  
2022 ◽  
Vol 1 (4) ◽  
pp. 714-721
Author(s):  
Lucas da Costa Santos ◽  
Lucas Santos do Patrocínio Figueiró ◽  
Alex Xavier Ribeiro Andrade ◽  
Antônio Costa Ferreira Neto ◽  
Caroline Salezzi Bonfá
Keyword(s):  
Meteorological Data ◽  
Irrigation Management ◽  
Absolute Error ◽  
Minas Gerais ◽  
Climatic Conditions ◽  
Empirical Methods ◽  
The North ◽  
And Performance ◽  
Evapotranspiration Estimation ◽  
E Mail

ESTUDO COMPARATIVO ENTRE METODOLOGIAS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA LOCALIDADES DO NORTE DE MINAS GERAIS     LUCAS DA COSTA SANTOS1; LUCAS SANTOS DO PATROCÍNIO FIGUEIRÓ1; ALEX XAVIER RIBEIRO DE ANDRADE1; ANTÔNIO COSTA FERREIRA NETO1 E CAROLINE SALEZZI BONFÁ1   1 Departamento de Agronomia, Universidade Federal dos Vales do Jequitinhonha e Mucuri – UFVJM, Campus JK, Rodovia MGT 367-KM 583, nº 5000, Alto da Jacuba. CEP: 39.100-000, Diamantina, Minas Gerais, Brasil. E-mail: [email protected];[email protected];[email protected]; [email protected]; [email protected].     1 RESUMO   A determinação da evapotranspiração é imprescindível para a prática racional da irrigação, o que tem conduzido à formulação de diversas equações para estimativa desta importante variável meteorológica. Nesse sentido, faz-se necessário estudos comparativos com estas equações de modo a avaliar, localmente, sua aplicabilidade. Em linha com o exposto, objetivou-se comparar, para as condições climáticas de Salinas e Januária (ambos situados no Norte de Minas Gerais, Brasil), métodos empíricos de estimativa da evapotranspiração com o método padrão de Penman-Monteith (FAO56). Para tanto, utilizou-se dados meteorológicos de cinco anos (2016 a 2020) obtidos do Instituto Nacional de Meteorologia (INMET). Para a análise comparativa foram utilizados os seguintes indicadores estatísticos: coeficientes de determinação (R²) e correlação (r), erro absoluto médio (EAM), raiz do erro quadrado médio (REQM), índice de concordância (d) e índice de desempenho (c). Os resultados obtidos demonstram que, para as duas localidades avaliadas, o método de Blaney-Criddle apresenta o melhor desempenho para a estimativa da evapotranspiração, por outro lado, as equações de Hargreaves-Samani e Priestley-Taylor exibiram performance insatisfatória.   Palavras-chave: métodos empíricos, demanda hídrica de cultivos, manejo da irrigação.     SANTOS, L. C.; FIGUEIRÓ, L. S. P.; ANDRADE, A. X. R.; FERREIRA NETO, A. C.; BONFÁ, C. B. COMPARATIVE STUDY BETWEEN REFERENCE EVAPOTRANSPIRATION ESTIMATION METHODOLOGIES FOR NORTHERN MINAS GERAIS LOCATIONS     2 ABSTRACT   The determination of evapotranspiration is essential for the rational practice of irrigation, which has led to the formulation of several equations to estimate this important meteorological variable. In line with the above objective was to compare, for the climatic conditions of Salinas and Januária (both located in the North of Minas Gerais, Brazil), empirical methods for estimating evapotranspiration with the standard method of Penman-Monteith (FAO56). For this purpose, meteorological data for five years (2016 to 2020) obtained from the National Institute of Meteorology (INMET) were used. For the comparative analysis, the following statistical indicators were used: coefficients of determination (R²) and correlation (r), mean absolute error (EAM), root mean square error (REQM), agreement index (d) and performance index (c). The results obtained demonstrate that, for the two locations evaluated, the Blaney-Criddle method presents the best performance for estimating evapotranspiration, on the other hand, the Hargreaves-Samani and Priestley-Taylor equations showed unsatisfactory performance.   Keywords: crop water demand, empirical methods, irrigation management.

scholarly journals WATER DEMAND, CROP COEFFICIENT AND UNCOUPLING FACTOR OF COWPEA IN THE EASTERN AMAZON

2017 ◽  
Vol 30 (1) ◽  
pp. 190-200 ◽  
Author(s):  
VIVIAN DIELLY DA SILVA FARIAS ◽  
◽  
MARCUS JOSÉ ALVES DE LIMA ◽  
HILDO GIUSEPPE GARCIA CALDAS NUNES ◽  
DENIS DE PINHO SOUSA ◽  
...  
Keyword(s):  
Water Demand ◽  
Irrigation Management ◽  
Gaussian Model ◽  
Crop Coefficient ◽  
Climatic Conditions ◽  
Degree Days ◽  
Local Conditions ◽  
Area Index ◽  
Crop Coefficients ◽  
Accumulated Degree Days

ABSTRACT Cowpea has great socioeconomic importance in the northeastern part of Pará state. However, in order to provide suitable irrigation management during the dry period this region requires solid information regarding water demand by regional crops. This research aims to determine the water demand, the crop coefficient (Kc) and the uncoupling factor during the different development stages of cowpea in the northeast of Pará. The crop evapotranspiration (ETc) was measured by drainage lysimeters. This information was coupled to the reference evapotranspiration (ETo) to obtain the crop coefficients, which were used to adjust the model function of accumulated degree-days and the leaf area index (LAI). The uncoupling factor was estimated to indicate the factors that control evapotranspiration. The ETc values reached a cumulative total of 267.73 mm ± 10.21 mm during the cowpea cycle. The average value of the uncoupling factor was 0.66. This indicates that the cowpea crop does not fully uncouple from the atmosphere underneath the climatic conditions in northeast Pará. The cowpea Kc values presented averages of 0.8, 1.4 and 0.8 in the vegetative phase, reproductive phase and final stage, respectively. The Gaussian model showed an excellent fit for the estimation of Kc values based on accumulated degree days and the LAI. These amounts differ from others found in the literature. Therefore, it reinforces the necessity for an assessment of crop coefficients under local conditions and for the employment of more precise methods.

scholarly journals Irrigation scheduling strategies for pepper based on evaporation and reference evapotranspiration

2021 ◽  
Vol 26 (51) ◽  
pp. 69-76
Author(s):  
Borivoj Pejić ◽  
Ivana Bajić ◽  
Ksenija Mačkić ◽  
Dušanka Bugarski ◽  
Slobodan Vlajić ◽  
...  
Keyword(s):  
Reference Evapotranspiration ◽  
Soil Layer ◽  
Open Water ◽  
Irrigation Scheduling ◽  
Climatic Conditions ◽  
Vegetable Crops ◽  
Irrigation Water Use ◽  
Evapotranspiration Rate ◽  
Crop Coefficients ◽  
Novi Sad

The experiment with drip irrigated pepper was conducted at the Rimski Šančevi experimental field of the Institute of Field and Vegetable Crops in Novi Sad in 2019. The irrigation was scheduled on the basis of the water balance method. Two methods were used to compute the daily evapotranspiration of pepper (ETd): reference evapotranspiration (ETo) and evaporation from an open water surface (Eo). Crop coefficients (kc) and corrective coefficients (k) were used to convert ETo and Eo values into ETd. Kc and k were 0.3-0.4, 0.6-0.7, 0.9-1.1, 0.8-0.9 and 0.4, 0.7, 1.0 and 0.8 for initial stage, crop development, mid season, and late season, respectively. ETo was calculated by the Hargreaves equation. Eo values were measured by a Class-A pan located at a meteorological station near the experimental plot. Irrigation started when readily available water (RAW) in the 0.3 m soil layer was completely absorbed by plants. Differences in crop yield (Y) and irrigation water use efficiency (IWUE) obtained using Eo (42.58 t ha-1, 15.20 kg m-3) and ETo (40.78 t ha-1, 14.56 kg m-3) were not statistically different. Evapotranspiration rate was 364.2 mm and 337.3 mm in Eo and ETo variant, respectively. The fact that the differences in Y and IWUE between different calculations of ETd were not statistically significant indicates that both methods can be recommended for irrigation scheduling programs for pepper in the climatic conditions of the Vojvodina region. However, priority should be given to ETo due to the easy accessibility and reliability of data.

scholarly journals Coeficiente del cultivo de Vigna unguiculata L. Walp. cv. INIAP-463 para periodos secos y lluviosos utilizando lisimetría de drenaje

2020 ◽  
pp. 29
Author(s):  
Jesús Enrique Chavarría Párraga ◽  
Julio Cesar Ramírez-Caicedo ◽  
Jorge Isaac Zambrano-Kuffó ◽  
Richard Xavier Bravo-Ferrín ◽  
Luis Enrique Párraga-Muñoz
Keyword(s):  
Vigna Unguiculata ◽  
Reference Evapotranspiration ◽  
Climatic Conditions ◽  
Weather Station ◽  
Phenological Stage ◽  
Dry Period ◽  
Rainy Period ◽  
Palabras Clave ◽  
Crop Cycle ◽  
Crop Coefficients

Coefficient of Vigna unguiculata L. Walp. for dry and rainy periods in the Chone river valley Resumen El uso del agua en la agricultura es una actividad muy demandante a nivel mundial, por ello es necesario conocer la cantidad de agua que consumen los vegetales de interés agrícola. Se investigó el coeficiente del cultivo (Kc) de Vigna unguiculata L. Walp. (cv. INIAP-463) para periodos secos y lluviosos de Chone, Manabí, Ecuador a través de lisimetría de drenaje. Se ejecutó en el año 2019, implementándose tres lisímetros de drenaje cerca de la estación climatológica M0162. La lámina de riego fue aplicada en base a la evapotranspiración de referencia diaria (ETo). Se realizó el cálculo del Kc para cada etapa fenológica del cultivo determinando el cociente entre la evapotranspiración del cultivo (ETc) y ETo. El frejol presentó cuatro etapas según su consumo hídrico, reportando valores de Kc de 0,55; 0,92; 1,30 y 0,80 para el periodo seco y 0,45; 0,88; 1,28 y 0,75 para el periodo lluvioso. Las necesidades hídricas del frejol fueron 219,37 mm para el período seco y 237,82 mm para el período lluvioso durante 85 días que duró el ciclo del cultivo. Los valores de Kc y necesidades hídricas varían según las condiciones climáticas de las zonas en donde se desarrollen los cultivos. Palabras clave: evapotranspiración; lámina de drenaje; necesidades hídricas; riego; leguminosa. Abstract Water use in agriculture is a very demanding activity worldwide, therefore it is necessary to know the amount of water consumed by vegetables of agricultural interest. The crop coefficients (Kc) of Vigna unguiculata L. Walp was investigated. (cv. INIAP-463) for dry and rainy periods of Chone, Manabí, Ecuador through drainage lysymmetry. It was executed in 2019, implementing three drainage lysimeters near the M0162 weather station. The irrigation sheet was applied based on the daily reference evapotranspiration (ETo). Kc was calculated for each phenological stage of the crop by determining the quotient between the evapotranspiration of the crop (ETc) and ETo. The bean presented four stages according to its water consumption, reporting Kc values ​​of 0.55; 0.92; 1.30 and 0.80 for the dry period and 0.45; 0.88; 1.28 and 0.75 for the rainy season. The water needs of the beans were 219.37 mm for the dry period and 237.82 mm for the rainy period during the 85 days of the crop cycle. The Kc values ​​and water needs vary according to the climatic conditions of the areas where the crops are grown. Keywords: evapotranspiration; drainage sheet; irrigation; water needs; legume.

scholarly journals Assessing the Impacts of Urbinization on the Climate of Kumasi

2018 ◽  
Author(s):  
Caleb Mensah ◽  
Julia Atayi ◽  
Amos T. Kabo-bah ◽  
Marian Švik ◽  
Daniel Acheampong
Keyword(s):  
Urban Areas ◽  
Geographical Location ◽  
Climatic Conditions ◽  
Climatic Data ◽  
Garden City ◽  
Landsat Images ◽  
Green Vegetation ◽  
City Model ◽  
The Impact ◽  
The City

The key anthropogenic effects on climate include the changes in land use and emission of greenhouse gases into the atmosphere. Depletion of vegetation poses serious threat that speeds the process of climate change and reduces carbon sequestration by the environment. Thus, the preservation of natural environment in urban areas is an essential component of the garden city model, proposed by Sir Ebenezer Howard in 1898, to ensure ecological balance. Recent Landsat images showed that Kumasi does not have the required percentage of green vegetation as was stipulated in the garden city model on which the city was built. It was observed that most parts of Kumasi's green vegetation have been lost to built environments. This study was conducted to assess the impact of urbanization on the garden city status and its effect on the micro-climate of the city. Significant changes in the vegetation cover of the city was evaluated from Landsat-TM imagery and analysis of a long term climatic data of Kumasi carried out over a 55-year period (1960 to 2015). It was observed that, climatic conditions have slightly changed, as mean surface temperature of has increased by 1.2 °C/ 55 years, due to the significant landuse changes from development of non-transpiring, reduced evaporative urban surfaces. However, the impact is not greatly felt due to the geographical location of the city on the globe despite the evidence of a considerable temperature change. Green vegetation conservation for the city is recommended as a top priority in future for city authorities and planners.

scholarly journals Evaluation of empirical methods to estimate reference evapotranspiration in Uberaba, State of Minas Gerais, Brazil

2012 ◽  
Vol 32 (5) ◽  
pp. 875-888 ◽  
Author(s):  
Giovani L. de Melo ◽  
André L. T. Fernandes
Keyword(s):  
Standard Method ◽  
Reference Evapotranspiration ◽  
Potential Evapotranspiration ◽  
Minas Gerais ◽  
Climatic Conditions ◽  
Empirical Methods ◽  
Monthly Data ◽  
And Performance ◽  
Simple Statistical Analysis ◽  
Climatic Elements

Evapotranspiration is the process of water loss of vegetated soil due to evaporation and transpiration, and it may be estimated by various empirical methods. This study had the objective to carry out the evaluation of the performance of the following methods: Blaney-Criddle, Jensen-Haise, Linacre, Solar Radiation, Hargreaves-Samani, Makkink, Thornthwaite, Camargo, Priestley-Taylor and Original Penman in the estimation of the potential evapotranspiration when compared to the Penman-Monteith standard method (FAO56) to the climatic conditions of Uberaba, state of Minas Gerais, Brazil. A set of 21 years monthly data (1990 to 2010) was used, working with the climatic elements: temperature, relative humidity, wind speed and insolation. The empirical methods to estimate reference evapotranspiration were compared with the standard method using linear regression, simple statistical analysis, Willmott agreement index (d) and performance index (c). The methods Makkink and Camargo showed the best performance, with "c" values of 0.75 and 0.66, respectively. The Hargreaves-Samani method presented a better linear relation with the standard method, with a correlation coefficient (r) of 0.88.

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