Penman-Monteith with missing data and Hargreaves-Samani for ETo estimation in Espirito Santo state, Brazil/Penman-Monteith com dados faltantes e Hargreaves-Samani para estimativa da ETo no estado do Espirito Santo, Brasil

The Penman-Monteith method (PM-FAO) is recommended as standard for calculation of reference evapotranspiration (ETo). However, its use requires a series of meteorological variables that is not normally available, restricting its application in many locations. A solution to the problem of unavailability of meteorological data was presented in FAO Bulletin 56, which contains methodologies for estimating wind speed, solar radiation and relative humidity. The objective of the present study was to evaluate the performance of the PM-FAO methodologies for missing data and Hargreaves-Samani as alternatives to the PM-FAO standard method at different time scales and seasons for the municipalities of Linhares and Sao Mateus, located in the northern region of the state of Espirito Santo. The comparison was performed using linear regression parameters ([[beta].sub.0] and [[beta].sub.1]), coefficient of determination, standard error of estimation (SEE) and coefficient of performance. The best alternative to the standard PM-FAO standard method for estimating ETo in the studied area was the Penman-Monteith method with missing wind speed data, since the [R.sup.2] for this method always remained above 0.94 and the confidence coefficient was classified as great, for all seasons and scales. The Hargreaves-Samani method did not present satisfactory performance, with [R.sup.2] below 0.7, regardless of the time scale and time of the year, and it yielded the greatest SEE (1.0 mm [d.sup.-1]) at spring on a two-day scale. Thus, its use in the northern region of the Espirito Santo state is not recommended. Key words: data scarcity, time scale, seasons RESUMO: O metodo de Penman-Monteith (PM-FAO) e recomendado como padrao para calculo da evapotranspiracao de referencia (ETo). Contudo, a sua utilizacao requer uma serie de variaveis meteorologicas que normalmente nao estao disponiveis, restringindo sua aplicacao em muitos locais. Uma solucao para o problema de indisponibilidade de dados meteorologicos, foi apresentado no boletim no. 56 da FAO, o qual contem metodologias para estimar velocidade do vento, radiacao solar e umidade relativa. O objetivo do presente estudo foi avaliar o desempenho das metodologias PM-FAO para dados faltantes e Hargreaves-Samani como alternativas ao metodo PM-FAO em diferentes escalas de tempo e estacoes do ano para as cidades de Linhares e Sao Mateus, localizadas na regiao norte do estado do Espirito Santo. A comparacao foi realizada utilizando os parametros