Evaluation and Modification of Valiantzas Models for the Reference Evapotranspiration Estimation by Lack of Data

Document Type : Original Article

Authors

1 Assistant Professor, Water Science and Engineering Department, Kashmar Higher Education Institute, Kashmar, Iran

2 Assistant Prof. Water & Science Engineering, Kashmar Higher Education Institute

Abstract

The precise estimation of reference crop evapotranspiration (ETo) has a significant role in improving water management in field and irrigation management. Different methods are available for ETo estimating. The FAO-PM equation is the most reliable method for ETo estimating, but this method requires large input data that is not fully measured in most meteorological stations. Also, the measured data lacks enough precision, especially in developing countries. Therefore, the researchers have used the empirical equations with minimum input data. In this study, the daily values of ETowere calculated at the synoptic station of Mashhad using Priestley-Taylor, Hargreaves, the FAO-PM proposed method by the lack of data and two forms of the Valiantzas equation. Then, the calculated values were compared with FAO Penman Monteith (PM) method. In this paper, new models for estimating ETo were presented by lack of wind speed and relative humidity data by modifying two forms of the Valiantzas equations. The results showed that by the lack of wind speed and relative humidity data, the modified Valiantzas model had the highest accuracy compared with the other methods. It was showed that the R2, RMSE and MAE indices were 0.85, 1 and 1.26 mm per day, respectively. Also, the results showed that the modified Hargreaves method had the highest accuracy when only temperature data is available.

Keywords

References

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