Investigating the Performance of Empirical Models for Estimating Reference Plant Water Requirements in Mianeh County
Subject Areas : Farm water management with the aim of improving irrigation management indicatorsFariborz Ahmadzadeh Kaleybar 1 , Ahad Molavi 2 *
1 - Assistance Professor, Department of Water Science and Engineering, Faculty of Agriculture and Natural Resources, Tabriz Branch, Islamic Azad University, Tabriz, Iran
2 - Assistance Professor, Department of Water Science and Engineering, Faculty of Agriculture and Natural Resources, Tabriz Branch, Islamic Azad University, Tabriz, Iran
Keywords: Evapotranspiration, regression coefficients, Empirical Models,
Abstract :
Background and Aim: Evapotranspiration is one of the most important factors of the hydrological cycle and its estimation is essential for a wide range of research including water balance, irrigation system design and management, simulation and modeling, and water resources planning. A model should be selected that can accurately estimate evapotranspiration according to regional conditions and using minimal climatic data. The aim of this research was to investigate the efficiency of different models for estimating evapotranspiration of reference plants, considering the FAO-Penman-Monteith model as the base model, and consequently to determine the most appropriate alternative model, considering the use of minimal data at the synoptic station of Mianeh County.
Method: The study site was the Mianeh Synoptic Station. This station is located in Mianeh County. Mianeh County is located in the southeastern corner of East Azerbaijan Province. To conduct this research and estimate the evapotranspiration rate of the reference plant, several meteorological parameters such as wind speed, average percentage of sunny hours, average monthly temperature, maximum monthly temperature, minimum monthly temperature, maximum monthly relative humidity, average monthly relative humidity, minimum monthly relative humidity, air pressure, and extraterrestrial radiation of the Mianeh Synoptic Station were used. The Visual Basic programming language was used to calculate the evapotranspiration of the reference plant. To evaluate the models for calculating the evapotranspiration of the reference plant, four categories of combined models (Penman-Writh, Allen-Penman- Pruitt), radiation (Doorenbos-Pruitt and Jensen-Haise), temperature (Linacre and Hargreaves) and the Ivanof moisture model were considered. The FAO-Penman-Monteith model was considered as a standard model to evaluate the performance of other models. The efficiency of the models was evaluated using five statistical indicators: root mean square error, mean average error, mean absolute error, coefficient of determination, and Jacovides criterion.
Results: The results showed that among the combined models groups, the coefficient of determination of the Allen-Penman- Pruitt model with a value of 0.859 had a relatively good agreement compared to the Penman- Writh model. Comparison of the ETP obtained from the Allen-Penman- Pruitt model and the base model showed that most of the resulting points were above the y=x line, which indicated an underestimation of this model compared to the baseline model. In the Penman-Writh method, the underestimation compared to the base model was evident in most cases with less intensity. In the radiation models category, the estimated ETP of the Jensen-Haise model had higher values than the standard model from April to August. The scatter of points in the diagram related to the Doorenbos- Pruitt model was greater than that of the Jensen-Haise method, which caused the coefficient of determination of this method to be lower than that of the Jensen-Haise method. Temperature models had the lowest average values of the statistical error indices RMSE and MAE. The highest coefficient of determination among the groups used was also related to these models. The agreement of ETPs obtained from Hargreaves and Ivanof models after applying regression coefficients with the results obtained from the standard model was greater than that of other models.
Conclusion: After applying regression coefficients in all models, the values of error indicators were significantly reduced, which indicates its positive effect on improving and increasing the performance of the models. The Hargreaves model with a correlation coefficient of 0.965 and an R/t criterion of 0.16 had the highest value among all models and had the best agreement and conformity with the base model. The Hargreaves model can be considered as a suitable alternative to the FAO-Penman-Monteith model for calculating the ETP of the Mianeh synoptic station, especially in terms of regression coefficients. Although the Ivanof moisture model had high error indicators of RMSE, MAE, MBE and the Jakovides criterion, but with a correlation coefficient of 0.963 and subsequent high agreement with the results of the standard method, this model can be recommended after the Hargreaves model by considering the regression coefficients for estimating the ETP of the Mianeh synoptic station.
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