Analysis and evaluation of important models for estimating the potential evapotranspiration

Evapotranspiration (consumptive use) is a key factor for estimating irrigation requirements and this depends on the climatic circumstance. Evapotranspiration (ETP) can be determined by direct measurements, empirical climatic formulas or by using evaporation measurements as indices. Direct measurement will give the best evaluation of ETP if it is available. In this research, 12 well-known climatic empirical methods have been selected from literature and used for estimating potential ETP under semi-arid areas which is similar to the northern part of Syria. The original data were derived and adapted from the meteorological station (Tel hadya, Jindiress and Breda), thus the purpose of this research is to select a few of the most popular methods for estimating the potential ETP in semi-arid areas. The methods used in this study were compared with the direct measurement methods (Class A Pan, Lysimeter). Daily and monthly potential ETP values were calculated and used for the statistical analysis which showed significant differences between the observed and expected values. The latter were calculated from the formulas of both Thornthwaite and Meyer. In conclusion, these two formulas were not applicable for the semiarid areas such as those prevailing in northern Syria. The other ten formulas were not significant and proved to be correct.