Estimate of evapotranspiration of reference on the northern Brazil

The aimed of this study was to evaluate the performance and the calibration methods contained in Sevap software for estimating reference evapotranspiration (ET0) for the Northern region of Brazil. The methodologies tested were Hargreaves-Samani, Jensen-Haise, Linacre, Makkink, Priestley & Taylor and Thornthwaite. The meteorological data needed to perform this work were taken from normal climatic (1961-1990) of 47 localities in northern Brazil, provided by the National Institute of Meteorology. The method taken as the standard was the Penman-Monteith FAO-56 and were realized regression analysis between the values obtained with the tested methodologies and values estimated by Sevap software. The calibration equations were performed by using coefficients "a" and "b" of the respective simple linear regression. The comparison of the results was by the coefficient of determination (r2), the coefficients "a" and "b" of the linear regression equations, standard error of estimate (SEE), concordance index of Willmott (d), the Pearson correlation coefficient (r) and confidence coefficient (c). Were analyzed the simple correlations between the values of ET0 obtained by the different methods and the measured climatic elements. It was found that the ET0 obtained by Penman-Monteith FAO-56, Jensen-Haise and Makkink were positively correlated with solar radiation. The Hargreaves-Samani and Priestley and Taylor were not showed correlated with any climatic element. The Linacre and Thornthwaite methods were positively correlated with the average and maximum air temperatures. After the calibration of the studied equations, the estimates of different methods were closer to ET0 values by Penman-Monteith. The method of Priestley & Taylor showed better performance than the other methods and can be used for reliable estimation of ET0 in northern Brazil. After being calibrated, the methodologies of Makkink and Jensen-Haise can be used in the estimation of ET0 on the Northern region of Brazil