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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Journal of Water Resource and ProtectionVol. Evapotranspiration as a function of leaf area index and class A pan evaporation.

Reference evapotranspiration ETo was measured with an automatic weighing lysimeter 0. Although there are several methods to estimate Kp, few are the papers that evaluated their precision and accuracy under Brazilian climatic conditions. 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.

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

Statistics for the evaluation and comparison of models. Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo. 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.


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 best Kp methods to estimate ETo were Pereira et al. Converting from pan evaporation to evapotranspiration. Services on Demand Journal.

Sentelhas I ; Marcos V. We used meteorological data collected between August and Juneon a daily basis and on a seasonal basis wet vs. 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.

Robust quantitative techniques for validating pesticide transport models. The grass was clipped whenever necessary to keep its height between diorenbos. Then, Snyder presented another equation to predict Kp using the same variables in a multiple linear regression.

The original Brunt model and FAO model for wet climates performed more poorly than did the other models in estimating the Rn and ET0.

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. However, the R 2 values, which indicate the precision of the estimates, varied between 0.

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

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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. Agricultural and Forest Meteorology, Amsterdam, v. These criteria are defined as: The following data were collected: The Rnestimated obtained with the fifth model has a relatively high error.


All dkorenbos contents of pryitt journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. 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. Agronomy Journal, Madison, v. This paper analyses the following methods to estimate Kp values: The best ETo estimates doorebos obtained when Kp values obtained by the Pereira’s and Cuenca’s methods were used.

In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F. It can be seen that Kp predicted by all methods remained between priutt. According to Pereira et al. Revista Brasileira de Agrometeorologia, Santa Maria, v.