What is reference crop evapotranspiration and how is it determined?
Reference crop evapotranspiration is the rate of evapotranspiration from a large uniform area, covered by green grass, 8 to 15 cm tall, which grows actively, completely shades the ground and which is not short of water (http://www.fao.org/docrep/S2022E/s2022e07.htm). In humid and semi-humid areas where water usually is not a limiting factor, grass is used as a reference ET crop. In arid or semiarid areas, alfalfa is often used as a reference crop.
