The FAO 56 Penman-Monteith (PM) equation for reference evapotranspiration (ETo) estimation requires climatic data that are often not available at most weather stations. To overcome the problem of climate data availability, the FAO-56 report describes several procedures to estimate ETo in the absence of solar radiation, relative humidity and wind speed data with their subsequent replacement. Based on this, this study aimed to compare the ETo estimated with the lack of wind speed or relative humidity or solar radiation data and the estimations using complete data for diverse locations within Minas Gerais State, Brazil. The comparison was performed using coefficient of linear regression and determination, the Willmott’s index of agreement and each method errors. As a result, it was found that in the absence of relative humidity and wind speed, the PM equation had small estimation errors. In contrast, for radiation data absence, errors were larger in relation to the other variables. With only maximum and minimum temperatures, the FAO 56-PM method outperformed the Hargreaves-Samani one.
missing data; reference evapotranspiration; penman-monteith method
