Engenharia Agrícola (Aug 2004)

Média diária do déficit de pressão de saturação do vapor d'água do ar e sua influência na vapotranspiração de referência pelo modelo de penman-monteith (FAO 56) em Piracicaba - SP Daily average of the saturation-vapor-pressure deficit of the air and its influence upon the reference evapotranspiration by penman-monteith model (FAO56) in Piracicaba, SP, Brazil

  • Gustavo B. Lyra,
  • Antonio R. Pereira,
  • Gilberto C. Sediyama,
  • Guilherme B. Lyra,
  • Alailson V. Santiago,
  • Marcos V. Folegatti

DOI
https://doi.org/10.1590/S0100-69162004000200011
Journal volume & issue
Vol. 24, no. 2
pp. 328 – 337

Abstract

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Utilizando-se como padrão as medidas lisimétricas de um gramado, avaliaram-se os resultados de estimativas de ETo obtidas com Dar_méd oriundos de 14 métodos para seu cálculo. Tais comparações permitiram separar os métodos de cálculo de Dar_méd em três grupos, ou seja: um grupo resultou sempre em superestimativa de ETo; em outro, a tendência foi de sempre subestimar, e no último a tendência foi de superestimar valores baixos (The results of the evapotranspiration obtained with the Dair_avg proceeding from 14 methods were evaluated, by using the lysimetric measures of a sward. These comparisons allowed to separate the Dar_avg calculating methods into three groups: a group always resulted into an overestimate ETo; in other one always tended to underestimating the ETo; and in the last tended to overestimating the low values (<4.5 mm day-1), while underestimating the high values of ETo. No significant statistical differences were observed (t test; p <0.05) in ETo as a function of the Dair_avg methods, when using the hourly average of the temperature and/or the air relative humidity in relation to those determined with the average of the maximum and minimum values of these elements. Among the methods proposed by paper FAO56, just the one using the average relative humidity to calculate the actual pressure (e a) showed a satisfactory estimate. The best estimates of ETo were obtained with the Dair_avg methods using the average of the air temperature in the determination of the saturation pressure (e s) and the average of the relative humidity for the actual pressure (e a). The use of saturation-vapor-pressure deficit of the air at a single time (from 9 or 10 a.m. local) as a representative of Dair_avg showed to be a satisfactory alternative in estimating the ETo under the climatic conditions of Piracicaba, SP, Brazil.

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