Abstract

TREZZA, Ricardo. Estimation of monthly reference evapotranspiration in Venezuela: Which method to be used?. Bioagro [online]. 2008, vol.20, n.2, pp.89-95. ISSN 1316-3361.

The calculation of crop water needs is based on accurate estimate of reference evapotranspiration (ET_o) for each particular zone, and in turn, the possible alternatives for estimations are subject to the limitation of meteorological information in each country. The purpose of this work was to analyze several available methodologies for the estimation of monthly reference evapotranspiration in Venezuela using meteorological data from different weather stations located in the country. It was found that the methodologies included in the publication FAO-56, particularly the Penman-Monteith, are the most applicable for the climatic conditions of the country. The Thornthwaite equation was not appropriate, nor the equations of the publication of FAO-24 such as Radiation and modified Penman, because they notably overestimate ET_o. The method of Blaney-Criddle could be considered for low altitude regions when just mean air temperature data are available. The FAO-56 Hargreaves method has a potential for application due to it just needs minimum and maximum air temperature data, although requires the calculation of adjusting parameters for each region.

Keywords : FAO-56, FAO-24; Penman-Monteith; Hargreaves.