Based on the long data series of six weather stations in North China,three
temperature-based ET_0(estimating) methods,namely
the Hargreaves,the McCloud and the
Thornthwaite,were evaluated by comparing their results with that of the FAO56-PM.Three indicators,namely mean deviation,correlation coefficient and(t-statistics),were used to compare yearly and monthly series estimated by the FAO56-PM and the
temperature-based methods.Results show that the Hargreaves agrees best with FAO56-PM,followed by the McCloud,and then the Thornthwaite.In terms of yearly value,the temperature-based methods significantly underestimate the FAO56-PM in most stations of North China,with the Hargreaves by 53.2~200.2 mm/year or 4.6%~15.1%,the Thornthwaite by 269.7~468.1 mm/year or 24.8%~35.8%,and the McCloud by 90.5~435.7 mm/year or 8.2%~40.5%.The agreement between the temperature-based and the FAO56-PM method varies with months,overestimating the latter in summer,and underestimating it in other seasons,particularly in winter.The Hargreaves reaches peak value in June,which agrees with that of the FAO56-PM.The Thornthwaite and the McCloud reach peak value in July,the month with the highest temperature,and apparently lag behind that of the FAO56-PM.The Hargreaves can be chosen preferably in North China where only air temperature is available.