Comparison among methods of estimate of evapotranspiration of reference in the north area of Bahia

To determine the water needs of a culture in conditions no-pattern, it is fundamental the knowledge of the reference evapotranspiration (ETo). The method of Penman-Monteith is considered by FAO, as pattern for estimate of ETo. However, in function of the number of meteorological variables used in that method, it has been using several other methods in the irrigation handling. The present work had as objective compares, through dear daily values for the method of Penman-Monteith, the acting of the method of the Class A pan and the methods of Hargreaves-Samani and Makkink for the north area of Bahia. The data used to esteem ETo were obtained in the automatic meteorological station of DTCS/UNEB, Juazeiro, BA. The results showed that the methods of Hargreaves-Samani and Makkink, that use as entrance variable the air temperature and global solar radiation, presented good acting, both with coefficient "c" = 0.76. The method of the Class A pan, although very used in the handling of the irrigation, it showed acting just to regulate, with coefficient "c" = 0.62.