AVALIAÇÃO E APLICABILIDADE DO COEFICIENTE DO TANQUE CLASSE “A” NO MÉDIO PAJEÚ, PERNAMBUCO

Abstract

The objective of this study was to propose monthly average values of Class “A” pan (Kp) for the Pajeu Middle region, as well as analyze the theirs effects in the estimate of agricultural crop evapotranspira- tion (ETc). Evaporation values of class "A" pan and daily weather data from a series of 1999 to 2011 were used. From the daily values of odd-numbered years were obtained monthly values of reference Kp (Kpref). That series was used in the implementation of six methods of estimation of the Kp. The values found have been sub- jected to an analysis of variance and t-test (p > 0.05). The performance of the Kp values was done by estima- tion of the accumulated ETc values of the six agricultural crops. It was verified that the Kpref provided the best statistical indexes and minor errors in the estimate of ETc. The methods of Pereira et al. and the FAO case A should the best estimates among those evaluated. On the other hand, the Snyder and FAO case B methods were those of the worst performances. The performance of the estimation of the ETc in the Middle Pajeu, using the evaporation values of Class "A" pan, is conditioned by the time of year and crop to be explored.