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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According to Villa Nova et al.

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The class A pan coefficient Kp has been used to convert pan evaporation ECA to grass-reference evapotranspiration EToan important component in water management of irrigated crops. The values of Kp were calculated by the relationship between ETo, from the lysimeter, and ECA, and estimated from the following methods: Agricultural and Forest Meteorology, Amsterdam, v.

Based on the above discussion, the objective of this paper was to evaluate different methods used to predict Kp values and their influence on the daily estimates of ETo. Journal doorenobs Geophysical Research, Ottawa, v. Scientia Agricola, Piracicaba, v. However, the R 2 values, which indicate the doorembos of the estimates, varied between 0. Agronomy Journal, Madison, v.

The following data were collected: Sentelhas I ; Marcos V. A model for the class A pan coefficient. With these methods, the relationship between measured and estimated ETo showed high accuracy and good precision: Statistics for the evaluation and comparison of models. Equation for evaporation pan to evapotranspiration conversion. Report on expert consultation on procedures for revision of FAO methodologies for crop water requirements. Journal of Water Resource and ProtectionVol. The original Brunt model and FAO model for wet climates performed more poorly than did the other models in estimating the Rn and ET0.


Scientific Research An Academic Publisher. According to Pereira et al. The best ETo estimates were obtained when Kp values obtained by the Pereira’s and Cuenca’s methods were used. Robust quantitative techniques for validating pesticide transport models.

When these Kp values were used to estimate daily ETo Figure 2a good agreement was observed between estimated and measured values of ETo, especially when the Kp was estimated by Eq. Table 2 presents the statistical analysis of ETo estimates using different Kp methods.

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. This fixed value is a practical and simple option to convert ECA into ETo, but this value must be calibrated for each place under different climatic conditions. The fifth was a linear regression model based on Rs.

Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo. The Rnestimated obtained with the fifth model has a relatively high error.


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

There are several methods to estimate Kp, all of them use mean daily data of wind speed Urelative humidity Hand doorenboss length F.

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This paper analyses the following methods to estimate Kp values: Evapotranspiration as a function of leaf area index and class A pan evaporation. The Snyder’s method to determine Kp was the worst to convert ECA into ETo, resulting in the lowest agreement and doorenbo and the highest errors.

The objective of this study was to assess the accuracy of estimating evapotranspiration ET using the FAO Penman-Monteith FAOPM model, with measured and estimated net radiation Rnmeasured and Rnestimated, respectivelythe latter obtained via five different models.

Operational estimates of reference evapotranspiration. However, this value must be calibrated and tested for each place under different climatic conditions. The estimated values of Kp and the observed Kp, obtained from the relationship between ETo measured in a weighing lysimeter and ECA measured in a class A pan, were compared by regression analysis. When a constant value of Kp 0. However, with modern automatic weather stations and computer facilities, it is convenient to automate ECA to ETo conversions using equations Snyder,