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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When these Kp values were used to estimate daily ETo Figure 2 xoorenbos, a good agreement was observed between estimated and measured values of ETo, especially when the Kp was estimated by Eq.
Most of the methods have shown that Kp value is highly dependent on surrounding conditions and is determined by U, H and F.
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The use of a doorebos 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. Converting doodenbos pan evaporation to 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. The use of an arbitrary and constant Kp 0. The fifth was a linear regression model based on Rs.
Agricultural and Forest Meteorology, Amsterdam, v.
The following data were collected: According to Pereira et al. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F. Although there are several methods to estimate Kp, few are the papers that evaluated their precision and accuracy under Brazilian climatic conditions. Statistics for the evaluation and comparison of models. Table 2 presents the statistical analysis of ETo estimates using different Kp methods.
The Rnestimated obtained with the fifth model has a relatively high error. Equation for evaporation pan to evapotranspiration conversion. The same routine was adopted to evaluate ETo estimates with the different Kp values.
When a constant value of Kp 0.
Revista Brasileira de Agrometeorologia, Santa Maria, v. Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo. Reference evapotranspiration ETo was measured with an automatic weighing lysimeter 0. Subsequently, Pereira et al. These criteria are defined as: With these methods, the relationship between measured and estimated ETo showed high accuracy and good precision: All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Pguitt License.
Class A pan coefficients (Kp) to estimate daily reference evapotranspiration (ETo)
We used meteorological data collected between August and Juneon a daily basis and on a seasonal basis wet vs. Robust quantitative techniques for validating pesticide transport models.
This paper analyses the following methods to estimate Kp values: There are several methods to determine Kp values, using wind speed, relative humidity and fetch length and conditions.
The best ETo estimates were obtained when Kp values obtained by the Pereira’s and Cuenca’s methods were used. However, with modern automatic weather stations doordnbos computer facilities, it is convenient to automate ECA to ETo conversions using equations Snyder, 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 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. In addition to the sensor readings Rnmeasuredfive different models were used in order to obtain the Rnestimated. Reference evapotranspiration based on Class A pan evaporation. 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 best Kp methods to estimate ETo were Pereira et al. Report on expert consultation on procedures for revision of FAO methodologies for crop water requirements.
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 ET, those estimates becoming progressively more accurate as the cloud cover diminished.
Evapotranspiration as a function of leaf area index and class A pan evaporation.