Glossary
Evapotranspiration (ET)
The combined loss of water to the atmosphere from evaporation (off soil and water surfaces) and transpiration (from plants). It is the standard measure of total water loss from vegetated land surfaces.
ET equations such as Penman-Monteith were developed for vegetated land and reference crops. Applied directly to open water they tend to over-predict loss unless they are adapted, because open water has no stomatal (plant) resistance and different surface energy behavior.