Calibration Methods for Estimation of Reference Evapotranspiration in Morro Do Chapéu, Bahia, Brazil

The objective of this work was to calibrate and to validate the methods of Camargo, Hargreaves and Samani, and Priestley and Taylor, according to the Penman-Monteith model, for the estimation of reference evapotranspiration (ETo), in the four seasons of the year for the municipality of Morro do Chapéu, Bahia. Climatological data from the conventional meteorological station belonging to the National Institute of Meteorology (INMET) were used, in the period of 18 years (2000-2018). The first 16 years were considered to adjust the parameters. The years of 2016 and 2017 were assigned as independent data to validate the adjustments. To analyze the results, it was used the root mean square error (RMSE in mm d-1), coefficient of determination (R2), systematic error (BIAS in mm d-1), and Willmott's concordance index. After adjusting the parameters, the three methods improved their performance in the estimation of ETo, however, the Camargo method presented high values of RMSE, reaching 0.41 mm d-1 during the spring. It is concluded that the calibrated methods of Hargreaves and Samani, and, Priestley and Taylor can be recommended for the estimation of the reference evapotranspiration, for planning and execution of irrigation projects in the municipality, regardless of the season.