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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These criteria are defined as: There are several methods to estimate Kp, all of them use mean daily data of wind speed Urelative humidity Hand fetch length F.

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 Doprenbos, those estimates becoming progressively more accurate as the cloud cover diminished. How to rpuitt this article.

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However, this value must be calibrated and tested for each place under different climatic conditions. Evapotranspiration as a function of leaf area index and class A pan evaporation. The original Brunt model and FAO model for wet climates pruiitt more poorly than did the other models in estimating the Rn and ET0.

Converting from pan evaporation to evapotranspiration. Scientia Agricola, Piracicaba, v. Class Doorennos pan coefficients Kp to estimate daily reference evapotranspiration ETo. Journal pruitg Water Resource and ProtectionVol. 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.

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


Robust quantitative techniques for validating pesticide transport models. Statistics for the evaluation and comparison of models. 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 paper analyses the following methods to estimate Kp values: Reference dporenbos 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. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from Doorenbis, H, and F.

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

It can be seen that Kp predicted by all methods remained between 0. Oruitt Research An Academic Publisher. According to Pereira et al. The same routine was adopted to evaluate ETo estimates with the different Kp values.

The following data were collected: Equation for evaporation pan to evapotranspiration conversion. Sentelhas I ; Marcos V.

When a constant value of Kp 0. The Rnestimated obtained with the fifth model has a relatively high error. Services on Demand Journal. Report on expert consultation on procedures for revision of FAO methodologies for crop water requirements.

All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Agricultural and Forest Meteorology, Amsterdam, v. Operational estimates of reference evapotranspiration.

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. Reference evapotranspiration based on Class A pan evaporation. Revista Brasileira de Agrometeorologia, Santa Maria, v. Journal of Geophysical Research, Ottawa, v.

Subsequently, Pereira doorenboe al. Class A pan evaporation Doorenbks was also measured in the weather station with a micrometric screw. A Note on a Recent Paper by J. There are several methods to determine Kp values, using wind speed, relative humidity and fetch length and conditions.

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 prutit conditions. The best Kp methods to estimate ETo were Pereira et al. According to Villa Nova et al.


However, the R 2 values, which indicate the precision of the estimates, varied between 0. Most of the methods have shown that Kp value is highly dependent on surrounding conditions and is determined by U, H and F. The estimated values of Kp and the observed Kp, obtained from the relationship between ETo measured in a weighing lysimeter dooenbos ECA measured in a class A pan, were compared by regression analysis.

The Snyder’s method to determine Kp was the worst to convert ECA into ETo, resulting in the lowest agreement and efficiency and the highest errors. Reference evapotranspiration ETo was measured with an automatic weighing lysimeter 0. The use of an arbitrary and constant Kp 0. Although there are several methods to estimate Kp, few are the papers that evaluated their precision and accuracy under Brazilian climatic conditions.

With these methods, the relationship between measured and estimated ETo showed high accuracy and good prjitt 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. 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.

Table 2 presents the statistical analysis of ETo estimates using different Kp methods. 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.