Comparison of Reference Crop Evapotranspiration Computing Methods on Manasi Basin

Based on the daily observation meteorological data on mosuowai、paotai、shihezi and wulanwusu weather station,daily reference crop evapotranspiration were calculated and compared by Penman-Monteith、Hargreaves,Priestley-Taylor methods from SWAT2000.Results showed that the result of Hargreaves is greater than Penman-Monteith and Priestley-Taylor is less than Penman-Monteith on mosuowai and paotai.Hargreaves is less than Penman-Monteith and Priestley-Taylor is close to Penman-Monteith on shihezi and wulanwusu.Hargreaves is no significant difference with Penman-Monteith by t-test on paotai,thus can substitute Hargreaves for Penman-Monteith;Priestley-Taylor is no significant difference with Penman-Monteith on mosuowai,shihezi and wulanwusu,can substitute Priestley-Taylor for Penman-Monteith.Three methods calculating reference crop evapotranspiration were remarkable relativity with evaporation,correlation coefficient were greater than 0.95 and can estimate ET0 by evaporation using regression formula.