Comparison of methods for calculating reference crop evapotranspiration in Haihe River basin of China

There are a lot of estimation methods for reference crop evapotranspiration (ET0)-, however, different parameters are required. Therefore, it is particularly important to find accurate alternative methods. Based on the data of ten weather stations in Haihe River basin for 30 years, ET0 was estimated with six methods, such as FAO-56 Penman-Monteith (PM), Hargreaves and Irmark-Allen etc. taking PM equation as the standard, the other methods were evaluated. The results showed that for stations except Wutaishan station in Haihe River basin, the estimated ET0 by the Hargreaves and the FAO-24 Radiation equations were closer to the values of ET0 estimated by the PM method than. by other methods. Therefore, it is concluded that Hargreaves methods can replace the PM method at these stations which are short of radiation and wind speed data; whereas, in Wutaishan Mountain area, the empirical parameters of the Hargreaves equations should be changed before being used in given local stations.