CALIBRAÇÃO DA EQUAÇÃO DE HARGREAVES-SAMANI PARA ESTIMAR A EVAPOTRANSPIRAÇÃO DE REFERÊNCIA NO ESTADO DO ESPÍRITO SANTO

Abstract

Most Brazilian localities do not have available meteorological data to estimate reference evapotranspiration (ET 0 ) by the standard Penman-Monteith (PM) method. Thus, methods that allow estimation of ET 0 using limited data become important. The present study consisted in calibrating the Hargreaves-Samani equation (HS) by different methods to estimate daily ET 0 in the state of Espírito Santo. Meteorological data from nine INMET automatic stations located in the state of Espírito Santo were used, being ET 0 calculated by the PM method used as reference for the calibration of the HS equation. The calibration was performed using the data from each meteorological station individually, by three different methods: adjust only the parameter H c of the HS equation; adjustment of the three parameters simultaneously (H c , H e and H t ); and ET 0 adjustment using simple linear regression. The adjusted equations obtained were evaluated through the coefficient of determination (r 2 ) of the simple linear regression and the root mean square error (RQME). Although calibration by simultaneous adjustment of the three parameters of the HS equation gave better results, its efficiency did not differ significantly from the other methods. Thus, considering the limitations of this method, it is concluded that the calibration using linear regression is the most indicated method. As a second option, calibration using the adjustment of the H c parameter of the Hargreaves-Samani equation is considered.