ABSTRACT
Water vapor loss from land surfaces depends on meteorological factors that provide the energy required to transform liquid into vapor and disperse the free water molecules into the atmosphere. The process can occur only if continuity in the gaseous phase between the liquid water and the atmosphere is established. More specifically, it depends also on the availability of liquid water in the vegetation and in the soil. The purpose of the potential and reference evapotranspiration concepts is to standardize liquid water availability.
