Estimating Daily Alfalfa to Grass Reference Evapotranspiration Ratios and Determining the Aerodynamic and Energy Balance Components Contribution in Evapotranspiration (Case study: East Azerbaijan Province)

Evapotranspiration (ET), as a major component of the hydrologic cycle, is important in water resources management and irrigation scheduling. Nowadays, due to the lack of the lysimetric data in weather stations, the ET values calculated by the standard FAO Penman-Monteith model ( ) are used for grass reference crop. Also, the Penman- Kimberly model is widely applied for computing the alfalfa-reference crop ET (ETr). In the present study, the meteorological data from 6 weather stations located in the East Azarbayjan Province covering a period of 10 years were used to calculate the and ETr values. Then, the ETr to ratios were computed for all six stations during the study period. Finally, the contributions of the energy balance and aerodynamic components on the final ET values were determined using the Penman- Kimberly model, which showed the important influence of the both components on the ET process. Consequently, the use of radiation-based models e.g. Priestly- Taylor model in these stations should be carried out by special care.