Analysis of reference evapotranspiration of Janaúba, Minas Gerais

Abstract

Knowledge of the reference evapotranspiration (ETo) is essential for the irrigation management of agricultural crops worldwide. The Penman Monteith demand different weather variables, which hinders its application in areas with few weather stations such as the north of Minas Gerais. This work, compare the method of Hargreaves Samani with Penman Monteith and determine the frequency of occurrence of the reference evapotranspiration in the city of Janaúba, MG. To assess the fit of Hargreaves Samani equation with Penman Monteith used the coefficient of determination (r2), the coefficient of correlation (r), the standard error of estimate (SEE), the index agreement (d) and the index performance (c). Kimball’s method was used for determining the frequency of occurrence. The results indicate that the Hargreaves Samani method overestimates the values of Penman Monteith at 8%, but in the monthly analysis, it is observed that between the months April to August Penman values were superior to Hargreaves. All statistical criteria used showed Hargreaves Samani fitted equation with a better assessment when compared with the Penman Monteith. The higher frequency of occurrence was between 4.5 and 4.7 mm day−1 (6.62%) and the equation that indicates the probability of being equaled or exceeded evaporation showed an r2 equal to 0.9676.