A modified Hargreaves equation by free search and its application in Harbin

摘要

The reference crop evapotranspiration (ET0) calculated from Hargreaves equation will be negative as the fixed parameters when mean air temperature is lower than −17.8°C. To improve the application of Hargreaves equation, Free Search was employed to solve the parameters of modifying Hargreaves equations based on 48-year daily meteorological data of Harbin, and the evaluation of the modified Hargreaves equations were verified by three time steps of daily, ten-day and monthly. The research results showed that the modified Hargreaves equations could solve the problem on the negative ET0, and its accuracy is identical with the verified Hargreaves equations recommended by FAO,when ET0 values calculated from Penman-Monteith equation was taken as standard. And what's more, a simple method for developing Hargreaves equation was developed then.