Evaluation of fourteen methods of estimation reference evapotranspiration (Case study: Mazandaran Province)

With the increase of population and pressure on water and soil resources, the important of agriculture and influential parameters in this field have increased more than before. One of these parameters is the evapotranspiration of the reference plant for irrigation planning, which is accurate estimation of that can play an important role in increasing water productivity. There are different methods for estimating the evapotranspiration of the reference plant that in this study, experimental methods in three general categories based on temperature, radiation and mass transfer and five different models of Valiantzas method by comparison with the FAO-Penman-Mantith method as reference method have evaluated. For this purpose, meteorological data of 10 synoptic stations of Mazandaran province in a 15-year period (2004-2018) were used. The results showed that between experimental methods based on temperature, Hargreaves-Samani method in six stations, Trajkovic method in two stations and Blaney-Kridel method in one station perform the best performance. Among the experimental methods based on radiation, Jensen-Hayes method in seven stations and Abtiv method in three stations have the best performance. The results indicated under-estimate for the estimation of the reference plant evapotranspiration by all three experimental methods based on mass transfer compared to the FAO-Penman-Monteith reference method. In all of the 10 stations investigated, the Trabert method was more accurate than the WMO and Maheringer methods and was closer to the FAO-Penman-Monteith reference method. All 5 different models of the Valiantzas method have under-estimates compared to the FAO-Penman-Monteith reference method. Valiantzas 4 model in six stations, Valiantzas 5 and 2 models each in two stations provided the best performance.