Potential evaporation
Encyclopedia
Potential evaporation or potential evapotranspiration (PET) is defined as the amount of evaporation that would occur if a sufficient water source were available. If the actual evapotranspiration
is considered the net result of atmospheric demand for moisture from a surface and the ability of the surface to supply moisture, then PET is a measure of the demand side. Surface and air temperatures, insolation, and wind all affect this. A dryland is a place where annual potential evaporation exceeds annual precipitation.
Thornthwaite
Where
is the estimated potential evapotranspiration (cm/month)
is the average daily temperature (degrees Celsius; if this is negative, use 
) of the month being calculated
is the number of days in the month being calculated
is the average day length (hours) of the month being calculated
is a heat index which depends on the 12 monthly mean temperatures 
.
Somewhat modified forms of this equation appear in later publications (1955 and 1957) by Thornthwaite and Mather.
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
is considered the net result of atmospheric demand for moisture from a surface and the ability of the surface to supply moisture, then PET is a measure of the demand side. Surface and air temperatures, insolation, and wind all affect this. A dryland is a place where annual potential evaporation exceeds annual precipitation.
ThornthwaiteC. W. ThornthwaiteCharles Warren Thornthwaite was an American geographer and climatologist. He is best known for devising a climate classification system, published in 1948, that is still in use around the world, and also for his detailed water budget computations of potential evapotranspiration...
equation (1948)
Where
is the estimated potential evapotranspiration (cm/month) is the average daily temperature (degrees Celsius; if this is negative, use ) of the month being calculated is the number of days in the month being calculated is the average day length (hours) of the month being calculated is a heat index which depends on the 12 monthly mean temperatures .Somewhat modified forms of this equation appear in later publications (1955 and 1957) by Thornthwaite and Mather.
See also
- EvaporationEvaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
- Water vaporWater vaporWater vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
- Water cycleWater cycleThe water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...
- Köppen climate classificationKöppen climate classificationThe Köppen climate classification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936...
External links
- ag.arizona.edu Global map of potential evaporation.