EQUAÇÃO DE HARGREAVES-SAMANI CALIBRADA EM DIFERENTES BASES TEMPORAIS PARA SETE LAGOAS, MG/HARGREAVES-SAMANI EQUATION CALIBRATED IN DIFFERENT TIME BASES FOR SETE LAGOAS, MG, BRAZIL

Reference evapotranspiration (ETo) data are required in several analysis related to the use of water resources, such as irrigation management, rainfall water balance, watershed management, etc. The FAO Penman-Monteith method (FAO-PM) is considered the standard for calculating ETo. However, the application of this method may be restricted by the lack of meteorological data. One of the alternative methods with the lowest data requirement is Hargreaves-Samani (HS), which usually needs local calibration for greater accuracy in the application. This study aimed to evaluate the performance of the Hargreaves-Samani method in its original form and calibrated in an annual, semester, quarterly and monthly basis, in comparison to the FAO-PM standard method, based on an extensive historical series of daily meteorological data (86 years) collected in the city of Sete Lagoas, MG. The coefficients and the exponent of the HS equation were calibrated by minimizing the mean absolute error (MAE). The KolmogorovSmirnov and Mann-Whitney tests, respectively, were used to evaluate the suitability of comparative tests and to determine the ETo probability distribution adjustments. The calibration of the HS method nullified the trend of systematic overestimation of the daily ETo values, compared to FAO-PM, reducing the MAE. Calibration at different time bases led to the approximation of the probability distributions of ETo calculated using the HS method. These data did not differ significantly from each other in comparison to that obtained with the FAO-PM method.