2.4 Reference evapotranspiration models
A total of 13 often-used ET0 models were selected for comparison, including three combination models (1963 Penman, FAO24 Penman and FAO-56 PM), seven radiation models, (Priestley-Taylor, De Bruin-Keijman, Makkink, Makkink (1957), Makkink (1967), IRMAK1 and IRMAK2) and three temperature-based models (Hargreaves, Hargreaves1, Hargreaves2), to compare their performance by using lysimeter measurement. The specific equations and parameters of these models are listed in Table 1.