Daily Reference Evapotranspiration Based on Temperature for Brazilian Meteorological Stations

Reference evapotranspiration data (ET0) are essential for certain classes of agrarian and environmental science studies. The standard model for calculating ET0 is the FAO Penman-Monteith (FPM), but its application may be difficult when meteorological data are scarce. The objective of this study was to evaluate alternative models to estimate ET0 when only air temperature data are available by using daily data from 22 meteorological stations in Brazil under different climate classifications. The data set was divided for model calibration and validation. In addition to the Hargreaves-Samani (HS) model in its original and locally calibrated (HSc) forms, one model based on the HS model (HSb), and two other models (PE and FPMead) were proposed. The values of performance statistics for the calibrated models were similar. In general, the FPMead model (mean absolute error between 0.39 and 0.79 mm day-1) was the best according to a Friedman test at a 5% significance level, followed by the PE, HSb, and HSc models. The best performances for the calibrated models were obtained for the stations in the humid tropical zone (Koppen climate classifications Cfa, Cfb, and Cwa) according to the statistical dimensionless measures.