Evaluation of Reference Evapotranspiration Calculation Methods Applied to the Climatic Conditions of Turkey

This study was carried out to determine the possible use of evapotranspiration estimation (combination) methods under different climatic conditions of Turkey. Reference evapotranspiration values were calculated according to Penman (1963; Original wind function), FAO-24 Corrected Penman, Penman (Daytime wind speed), Kimberly–Penman (1972), Kimberly–Penman (1982), FAO-PPP-17, Penman (Merva-Fernandez), Penman–Monteith and Penman–Monteith (FAO) for selected 20 locations with different climatic conditions. Reference evapotranspiration (ET0) assessments were analyzed according to their annually, 8 monthly (March–October) and 3 monthly (June–August) values. In all periods evaluated, almost the same significant differences (P<0.01) were found between locations and methods. High ET0 values were obtained in the locations with high wind speed and low relative humidity. Low ET0 values were observed in the locations with low daily sunshine duration. In conclusion, FAO-PPP-17, Penman (Merva-Fernandez), Penman-Monteith and Penman-Monteith (FAO) could be more efficiently used. Penman (Daytime wind speed) and FAO-24 Corrected Penman over-predicted ET0 values as compared to other methods.