Estimativa da evapotranspiração de referência a partir da equação de Penman-Monteith, de medidas lisimétricas e de equações empíricas, em Paraipaba, CE. / Reference evapotranspiration estimated by penman-monteith equation, lysimetric measures and empirical equations in Paraipaba, state of Ceará, Brazil.

AUTOR(ES)

Almiro Tavares Medeiros

DATA DE PUBLICAÇÃO

2002

RESUMO

The irregular distribuition of rain in the Brazil’s northeast region become irrigation very important, being the main rational alternative to produce food. In an irrigation project the crop evapotranspiration (ETc) is the most important variable, which determine how much water is necessary to be applied to maintain the yield at high levels. Being ETc funcion of reference evapotranspiration (ETo), the determination of this variabel is fundamental in irrigation projects and schedule. In this context, this study aimed to evaluate ETo estimates from lysimetric measures and other methods, which were compaired with the ETo values obtained by Penman-Monteith equation (Allen et al., 1998). The methods used were: Thornthwaite (1948), Thornthwaite modified by Camargo et al. (1999), Class A pan (Allen et al., 1998), Hargreaves &Samani (1985) and Priestley-Taylor (1972). The data were analysed during the period from march to june, in 1997 and 1998. The meteorological data were collected in an automatic weather station located at Vale do Curu Experimental Station, in the Tropical Agroindustry National Research Center, belonged to EMBRAPA, in Paraipaba, State of Ceará, Brazil, where a weighing lysimeter using strain gauge was installed (area = 2,205m2). The data analysis were based on daily, quinquidial and decendial time scale, and were done utilizing regression analysis, agreement (Willmott, 1981) and performance (Camargo &Sentelhas, 1997) indexes, and the following errors: absolute mean error (EMA), maximum error (EM), sistematic error (Es) and random error (Ea). The results obtained showed that ETo lysimeric measures did not fit well with ETo estimated by Penman-Monteith equation in all time scales evaluated, what problably is related to the problems in the operation and maintenance of this equipament. In relation to the other methods to estimate ETo, the best fits were obtained with Priestley-Taylor (1972), for daily and decendial data, and with Thornthwaite modified by Camargo et al. (1999), for quinquidial data. Howerer, these methods presented sistematic errors, being proposed adjusts in the parameters f for the Thornthwaite modified by Camargo et al. (1999) and α for the Priestley-Taylor methods, which were modified, recpectively, to 0.379 and 1.19. With these modifications these methods improved the ETo estimation, increasing the accuracy and decreasing the errors, being classified by the performance index as good and very good, indicating their potenciality for be used in similar climatic conditions of this study, where complete set of weather data are not available.

ASSUNTO(S)

modelo penman-monteith irrigação estimativa vapotranspiration evapotranspiração irrigation soil-water-plant-atmosphere relationship lisimetro relação solo-água-planta-atmosfera estimation lysimeter penman-monteith s model

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