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The Pruitt and Doorenbos version of the Penman equation developed from Doorenbos J, Pruitt WO () Guidelines for predicting crop water requirements. Doorenbos, J. and W.O. Pruitt. Crop water requirements. FAO Irrigation and Drainage Paper No. Food and Agric. Organiz. of the U.N. Rome. Fereres. method of Department Irrigation and Drainage, Doorenbos and Pruitt and Doorenbos and Pruitt ();day/night wind ratio = 3, PM=Penman-Monteith ( Smith.

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The atmospheric pressure was determined by aneroid barograph, and sunshine duration was quantified with a Campbell-Stokes recorder. This fixed value is a practical and simple doorengos to convert ECA into ETo, but this value must be calibrated for each place under different climatic conditions. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F. Subsequently, Pereira et al.

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Agricultural and Forest Meteorology, Amsterdam, v. We used meteorological data collected between August and Juneon a daily basis and on a seasonal basis wet vs.

Operational estimates of reference evapotranspiration. According to Pereira et al. Kpseveral performance criteria were used including regression analysis, agreement index Dmean absolute error MAEmaximum absolute error MAXEand efficiency EFas suggested by Willmott et al.

The estimated values of Kp and the observed Kp, obtained from the doirenbos between ETo measured in a weighing lysimeter and ECA measured in a class A pan, were compared by regression analysis. The values of Kp were calculated by the relationship between ETo, from the lysimeter, and ECA, and estimated from the following methods: On the other days there were operational difficulties with this kind of lysimeter because of high intensity rainfall and wind which resulted in uncertainties and errors as described by Dporenbos et al.


Most of the methods have shown that Kp value is highly dependent on surrounding conditions and is determined by U, H and F. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Equation for evaporation pan to evapotranspiration conversion.

Class A pan coefficients (Kp) to estimate daily reference evapotranspiration (ETo)

Revista Brasileira de Agrometeorologia, Santa Maria, v. This fixed value is a simple and practical option to convert ECA in ETo, without the need of weather data as wind speed, relative humidity and temperature.

Table 2 presents the statistical analysis of ETo estimates using different Kp methods. The best ETo estimates were obtained when Kp values obtained by the Pereira’s and Cuenca’s methods were used.

This paper analyses the following methods to estimate Kp values: Scientific Research An Academic Publisher.

With these doorenbso, the relationship between measured and estimated ETo showed high accuracy and good precision: The use of an arbitrary and constant Kp 0. Scientia Agricola, Piracicaba, v. Robust quantitative techniques for validating pesticide transport models. In overcast conditions, the original Brunt model, the FAO model for wet climates, the FAO model for dry climates, the FAO model and the model of linear regression with Rs as the predictor variable tended to overestimate Rn and ET, those estimates becoming progressively more accurate as the cloud cover diminished.

Report on expert consultation on procedures for revision of FAO methodologies for crop water requirements. The use of a constant value of Kp showed to be a simple and practical option odorenbos convert ECA into ETo, however, this value must be calibrated and tested for different climatic conditions. Statistics for the evaluation and comparison of models. The following data were collected: Journal of Geophysical Research, Ottawa, v.


The Snyder’s method to determine Kp was the worst to convert ECA into ETo, resulting in doorwnbos lowest agreement and efficiency and the highest errors. Then, Snyder presented another equation to predict Kp using the same variables in a multiple linear regression.

Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo. The grass was clipped whenever necessary to keep its height between 0.

Class A pan evaporation ECA was also measured in the weather station with a micrometric screw. Converting from pan evaporation to evapotranspiration. According to Villa Nova et al. Reference evapotranspiration based on Class A pan evaporation. The original Doordnbos model and FAO model for wet climates performed more poorly than did the other models dooorenbos estimating the Rn and ET0. The fifth was a linear regression model based on Rs. Sentelhas I ; Marcos V. A Note on a Recent Paper by J.

However, the R 2 values, which indicate the precision of the estimates, varied between 0. Reference evapotranspiration ETo is an essential component for use in water supply planning and irrigation scheduling Snyder, since the crop evapotranspiration ETc is estimated by ETo multiplied by the crop coefficient Kc.