Abstract
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.
Highlights
The reference evapotranspiration (ETo) has fundamental role in the study and determination of water relations in the activities of rural engineering
Several authors have been demonstrating the influence of climate type on the estimated ETo, as well as on the performance of alternative methods (Lemos Filho et al, 2010; Silva et al, 2011)
The results showed that the evaluation of performance of alternative methods estimating ETo for different climate types is essential when climatic data required for estimada como o método de Penman-Monteith American Society of Civil Engineers (ASCE) (EToPM) are unavailable or unreliable
Summary
The reference evapotranspiration (ETo) has fundamental role in the study and determination of water relations in the activities of rural engineering. Besides that, it is one of the most important hydrological variables for crop evapotranspiration, estimation and interpretation of agricultural water balances and irrigation management (Blaney and Criddle, 1950; Xu and Singh, 2005). Even considering the different climate database of meteorological data around world, as World Climate Database (Hijmans et al, 2005), the complete set of data needed to estimate ETo by Penman-Monteith method is not available, because key variables such as wind speed, solar radiation, daily insolation and relative humidity are still missing or not consistent
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