Avaliação do coeficiente do tanque classe “A” na estimativa da evapotranspiração de referência no baixo São Francisco, SE

Abstract

The scientific technical literature cites several methods to estimate the Class “a”tank coefficient (Kp) in order to obtain the reference evapotranspiration (ETo), which is vitally important in water management in agriculture. Most of these methods takes into account the relative humidity, the area surround and wind speed. The Class "A"tank methodis simple and consists in using a direct evaporation tank full of water, where measurements are made in millimeters of water evaporated from a reading toanother. A (ETo) is an important factor for those who use irrigation as a means to supply the water needs of crops, particularly in semi-arid regions. This study aimed to determine "A"class tank coefficients (Kp) through Snyder methods (1992), Pereira et al. (1995), Cuenca (1989), and Allen et al. (1998).Then,an estimate (ETo)was madeby using data from the evaporation of Class "A" (ACE), for the conditions of the lower São Francisco River region inthe State of Sergipe. The methods were evaluated in the annual wet and dry seasons for the year 2014. Later a correlation analysis was performed (ETo),estimated by each method front (ETo),estimated bythePemann-Montheith model. The coefficients of determination (r2), correlation (r), agreement (d) of Willmott (1982) and performance (c)were also determined. The results showed that along the annual dry and rainy season, all methods showed great performance. In the correlations performed by using thePenamn-Monteithmodel as a standard versus the methods used, the results were not satisfactory, with a low correlation.