Applicability of simple estimating method for reference crop evapotranspiration in Loess Plateau

Some methods for estimating reference crop evapotranspiration (ET0) are widely used in regions with insufficient meteorological data, but their applicabilities should be evaluated. The performances of six simple methods for estimating ET0 (i.e. FAO-24 Rad, FAO-24 BC, Hargreaves, Priestley-Taylor, Makkink and Turc) are evaluated based on the meteorological data from 48 stations during 1961－2009 in the Loess Plateau. Results showed that FAO-24 BC and Hargreaves equations were satisfactory to estimate annual ET0 while Makkink and Priestley-Taylor methods are not. The estimation errors of annual ET0 mainly come from those in November to March, while in April to October were very small. Spatial variability exist in the applicability of the six methods. FAO-24 BC and Hargreaves performs better at most stations while the other methods, especially for Makkink and Priestley-Taylor, provide unsatisfactory results. Most methods are not suitable for estimating ET0 in the southwest region except for Priestley-Taylor. Overall, FAO-24 BC and Hargreaves are recommended as the priority simple methods for calculating ET0 in the Loess Plateau.