Abstract: The reference evapotranspiration of the Alpine Meadows in the Haibei area was estimated by using the FAO P-M equation,Penman equation and Irmark-Allen equation.Calculations from the first method was considered as the standard to compare with those from other two methods.Results showed that the reference evapotranspiration was about 812.0mm in the Haibei alpine meadow,while it was 500.9mm in plant growing season from May to September.The comparison also suggested that the calculated reference evapotranspiration by FAO P-M was more reasonable,for there might be deviations by using the other 2 methods due to the influence of radiation and soil heat flux.Furthermore,the actual evapotranspiration was calculated by water balance,which was 425.5mm in plant growing season.Crop coefficient was the ratio between the actual and the reference evapotranspiration(by FAO P-M method),which was 0.51,0.96 and 0.87 in the beginning,middle and end of the growing season,respectively.

Key words: Reference evapotranspiration, Reference evapotranspiration, Crop coefficient, FAO P-M equation, Penman equation, Irmark-Allen equation