What is ETo?

ET: Evapotranspiration (ET) is the loss of water into the atmosphere by the combined processes of evaporation from soil and plant surfaces and transpiration from plants. ETo is evapotranspiration from standardized vegetation (grass or alfalfa) with known biophysical characteristics. Standardized vegetation, commonly known as reference vegetation or reference crop, is required because different plants have different biophysical characteristics and it is not practical to formulate equations for each plant type under different sets of conditions. The standard reference surface for ETo estimation at most CIMIS stations is a well-irrigated clipped grass.