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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All the contents of this journal, except where otherwise noted, is licensed under a Pguitt Commons Attribution License. However, the R 2 values, which indicate the precision of the estimates, varied between 0.

Agronomy Journal, Madison, v. How to cite this article. 1977 fifth was a linear regression model based on Rs. The use of an arbitrary and constant Kp 0. Subsequently, Pereira et al. Scientific Research An Academic Publisher. Evapotranspiration as a function of leaf area index and class A pan evaporation.

The best Kp methods to estimate ETo were Pereira et al. Then, Snyder presented another equation to predict Kp using the same variables in a multiple linear regression. Services on Demand Journal.

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The atmospheric pressure was determined by aneroid barograph, and sunshine duration was quantified with a Campbell-Stokes recorder. Converting from pan evaporation to evapotranspiration. The values of Kp were calculated by the relationship between ETo, from the lysimeter, and ECA, and estimated from the following methods: 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.


Kpseveral performance criteria were used including regression analysis, agreement index Dmean absolute error MAEmaximum absolute error MAXEand efficiency EFas suggested by Willmott et al.

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. There are several methods to determine Kp values, using wind speed, relative humidity and fetch length and conditions.

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

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.

Reference evapotranspiration based on Class A pan evaporation.

With these methods, the relationship between measured and prujtt ETo showed high accuracy and good precision: Revista Brasileira de Agrometeorologia, Santa Maria, v. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F. 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.

The best ETo estimates were obtained when Kp values obtained by the Pereira’s and Cuenca’s methods were used.

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.

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 Pereira et al. Report on expert consultation on procedures for revision of FAO methodologies for crop water requirements. Most of the methods have shown that Kp value is highly dependent on surrounding conditions and is determined by U, H and F. The Rnestimated obtained with the fifth model has a relatively high error.


The following data were collected: The grass doorwnbos clipped whenever necessary to keep its height between 0. Reference evapotranspiration ETo is an essential component for use in water supply planning and irrigation doorenboe Snyder, since the crop evapotranspiration ETc is estimated by ETo multiplied by the crop coefficient Kc. When a constant value of Kp 0.

Robust quantitative techniques for validating pesticide transport models. Table 2 presents the statistical analysis of ETo estimates using different Kp methods. Sentelhas I ; Marcos V.

However, this value must be calibrated and tested for each place under different climatic conditions. 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. There are several methods to estimate Kp, all of them use mean daily data of wind speed Urelative humidity Hand fetch length F. Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo.

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