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 same routine was adopted to evaluate ETo estimates with the different Kp values. Four of those models consider the effects of cloud cover: With these methods, the relationship between measured and estimated ETo showed high accuracy and good precision: The following data were collected: How to cite this article. Scientia Agricola, Piracicaba, v. Reference evapotranspiration ETo was measured with an automatic weighing lysimeter 0.

Statistics for the evaluation and comparison of models. Then, Snyder presented another equation to predict Kp using the same variables in a multiple linear regression. However, with modern automatic weather stations and computer facilities, it is convenient to automate ECA to ETo conversions using equations Snyder, Subsequently, Pereira et al. We used meteorological data collected between August and Juneon a daily basis and on a seasonal basis wet vs.

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Agricultural and Forest Meteorology, Amsterdam, v. The original Brunt model and FAO model for wet climates performed more poorly than did the other models in puritt the Rn and ET0. A model for the class A pan coefficient. Operational estimates of reference evapotranspiration. There are several methods to determine Kp values, using wind speed, relative humidity and fetch length and conditions.


Services on Demand Journal. It can be seen that Kp predicted by all methods remained between 0. These criteria are defined as: Equation for evaporation pan to evapotranspiration conversion.

Journal of Geophysical Research, Ottawa, v. 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. According to Villa Nova et al.

However, this value must be calibrated and tested for each place under different climatic conditions. Converting from pan evaporation to evapotranspiration. However, the R 2 values, which indicate the precision of the estimates, varied between 0.

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 use of a constant value of Kp showed to be a simple and practical option to convert ECA into ETo, however, this value must be calibrated and tested for different climatic conditions.

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


All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. 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. The Rnestimated obtained with the fifth model has a relatively high error. A Note on a Recent Paper by J.

Class A pan evaporation ECA was also measured in the weather station with a micrometric screw. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F. Evapotranspiration as a function of leaf area index and class A pan evaporation.

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

When a constant value of Kp 0. 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. Journal of Water Resource and ProtectionVol. The fifth was a linear regression model based on Rs. The use of an arbitrary and constant Coorenbos 0.

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