Estimate of potential evapotranspiration from energy balance method compared to evaporation pan and FAO Penman-Monteith methods

The purpose of this study was to determine the potential evapotranspiration (ETo) using energy balance and evaporation pan methods compared to the FAO Penman-Monteith method. The study area is located in West Azerbaijan province, approximately 37 km north of Urmia. In this research, the data of the Kahriz synoptic meteorological station data was used for a period of 7 months from April to October 2006 through 2008. After analyzing the data, the potential evapotranspiration was determined daily and monthly in all three methods. The results showed that ETo estimation in energy balance method was more accurate than evaporation pan method. The maximum and minimum ETo three-year average in the energy balance method (calculated with a reflection coefficient of α =25%) was 8.5 and 2.7 mm per day, respectively. While these values were 6.5 and 0.9 in the evaporation pan method, respectively, and FAO Penman-Monteith method was 11.3 and 2.9 mm per day, respectively. In the energy balance method, the mean three-year values of the Bowen ratio (β) and solar net radiation (Rn calculated with a reflection coefficient of 25%) were between -0.4134 to -0.2443 and 7.1 to 8.4 mm per day, respectively. In the pan evaporation method, the coefficient of Pan (KP) was calculated to be between 0.45 and 0.82.