Avaliação do método de Penman Monteith FAO 56 com dados faltosos e de métodos alternativos na estimativa da evapotranspiração de referência no Submédio Vale do São Francisco

Objective to evaluate the performance of the Penman Monteith method parameterized on the 56 FAO Bulletin (PMFAO56) with the absence of data and of alternative methods for the estimation of reference evapotranspiration in the Submedium Valley of San Francisco. Weather variables for the period March 2003 to April 2008 were used of five automatic stations belonging to the network of Embrapa semi-arid. In the evaluation of this method were considered to be different combinations as the lack of measurement of meteorological variables (radiation balance, global solar radiation, temperature and relative humidity, and wind speed), and alternative methods of Hargreaves and Samani, Jensen and Haise and Makkink. The performance was analyzed by means of indices and statistical errors. The results revealed that the PM-FAO56 has good estimates of ETo values when the absence of data is limited to the variables of relative humidity, for the estimation of the water vapor partial pressure, and, or, the wind speed, as soon as the square root of the square of the average error was less than 0.65 mm day -1 , when there is no data of these two variables at the same time. The estimation of the radiation balance values despite the good precision and accuracy in most weather stations (r 2 > 0.93 and angular coefficient < 1.19) raises the miscalculation of ETo in the region. Alternative methods of