Performance of different methods to estimate reference evapotranspiration in Cruz Alta - RS

The objective of this work was to evaluate the performance of different methods to estimate reference evapotran­spiration (ETo) in the municipality of Cruz Alta - RS, using the Penman-Monteith method as standard. Daily mete­orological data were collected from the Automatic Meteorological Station of the National Meteorological Institute (INMET), located in the municipality of Cruz Alta - RS, for a 10-year period. ETo was determined using the meth­ods of Penman-Monteith, Priestley-Taylor, Hargreaves-Samani, Benevides-Lopes and Jensen-Haise, comparing the standard method with the other methods used for three subgroups of data: analysis of the average of 10 years of observations and periods of high and low solar radiation. In order to establish the best methods for estimating ETo, we used: linear regression analysis, root mean square error (RMSE), mean absolute error (MAE), agree­ment index (d), and performance index (c), with classes established by Camargo and Sentelhas. Among the methods evaluated for the climatic conditions of Cruz Alta - RS, the Priestley-Taylor method is the one that pre­sents the best performance in ETo estimation, followed by the Hargreaves-Samani method, which can be used in daily and annual determinations, and in periods of high solar radiation. Due to the poor performance presented by the Jensen-Haise method, its use is not recommended.