The present research aimed to accomplish a comparison between the reference method of estimation of evapotranspiration, Penman-Monteith, considered as the standard method by FAO, with Penman-Piché method, which uses measurements of the evaporation from the Piché's evaporimeter. The period from January 2003 to December 2008 was analyzed considering daily data of air temperature, solar radiation, relative humidity of air and wind speed, which were collected with an automatic weather station, located in the Experimental Farm of University of Uberaba, in Uberaba, in the State of Minas Gerais, Brazil. Correlation coefficient (r), Willmott agreement index (d) and confidence index (c), which is the product between "r" and "d", were used in the comparison between reference evapotranspiration estimated by Penman-Monteith (ETpm) and Penman-Piche (ETpi). It was concluded that it is possible to estimate the reference evapotranspiration in a satisfactory manner through the evaporation measured by the Piche's evaporimeter. In the months of low relative humidity of air, the evapotranspiration estimated by the method which considers the measures of Piche's evaporimeter shows reduction in precision, with "r" values of 0,70; 0,78 and 0,70, respectively for the months of June, August and September of the studied series.
evaporimeter; irrigation; atmometer
