Alternative Methods of Reference Evapotranspiration for Brazilian Climate Types

Abstract The choice of consistent alternative methods is essential for the improvement of reference evapotranspiration (ETo) estimation for different climatic regions. Due to a critical gap in knowledge concerning the most adequate alternative ETo methods for the climatic conditions in Paraná, Brazil, this study aimed to test and to evaluate the main estimation alternative methods (Thornthwaite - EToTH; Camargo - EToC; Hargreaves and Samani - EToHS; Linacre - EToL; and, Budyko - EToB) for the subtropical (Cfb) and semi-arid (Bsh) climate types in Brazil. We compared our results with standard EToPM (Penman-Monteith) estimated between 1970 and 2015, using the minimum and maximum air temperature (T), sunshine hours (n), relative humidity (RH) and wind speed (U2). Least square regression analysis of ETo estimated by alternative methods vs EToPM were used to calibrate the methods for each analyzed climate type. The performance of calibrated and noncalibrated methods was evaluated by index of agreement “d” and performance “c”, root mean square error (RMSE) and mean error (ME). Our results showed the importance of calibration process of alternative methods for the improvement of ETo estimations in Brazil. The Hargreaves and Samani and Linacre calibrated methods showed better performance in the subtropical and semi-arid climates, respectively. Also, the Linacre and Budyko calibrated methods were particularly robust in subtropical and semi-arid climates, outlining the importance of continuous measurements of T used in the EToL and EToB modeling effort. The results presented here showed the importance to calibrate the alternative methods on ETo estimations and outlined the need for improvement and proposition of new ETo methods based on a limited number of climatic variables commonly available in subtropical and semi-arid climates in Brazil.