ABSTRACT
Weather station data are increasingly being used to calculate reference evapotranspiration (ETref), for purposes of irrigation system planning, design, scheduling, and management. There is a range of methods used to calculate ETref. The Food and Agricultural Organization (FAO) of the United Nations, in collaboration with the International Commission for Irrigation and Drainage (ICID) and the World Meteorological Organization (WMO), has recommended the Penman-Monteith method (referred to as FAO56-PM) to calculate ETref.
