Evapotranspiracao de referencia; validacao de metodologias de calculo para Portugal Continental

For a good water management in agriculture, a correct knowledge of the water consumption by the crops is needed. In the last decades, crop evapotranspiration (ET_c) was determined based on a two-step approach, using a reference evapotranspiration (ET_o) and a crop coefficient, that is a function of the crop itself and its development stage. FAO, in collaboration with I CID, has recommended the revision of methodologies for estimating crop water requirements. Grass reference evapotranspiration (ET_o) is now defined as the rate of evapotranspiration from a hypothetical reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 s m"-"1 and an albedo of 0.23, closely resembling the evapotranspiration from a extensive surface of green grass of uniform height, actively growing and with adequate water. The new ET_o definition provides for using a standardized Penman-Monteith equation to represent the hypothetical reference. All calculations and parameters have been revised. All these methods have been tested. Alternative processor's are proposed, but requiring local calibration. The main problem for a good implementation of this procedures is the reliability of the available meteorological data. This was confirmed for Coruche and, later, at national level. Several correction procedures have been successfully tested. At last, general results confirm the validity of the new concept of ET_o as a good instrument to obtain reliable data of evapotranspiration at reference conditions. Great efforts must be done to improve the quality of the meteorological data for agricultural proposes in PortugalAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga