# Potential evaporation

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.

${\displaystyle PET=16\left({\frac {L}{12}}\right)\left({\frac {N}{30}}\right)\left({\frac {10\,T_{a}}{I}}\right)^{\alpha }}$

Where

${\displaystyle PET}$ is the estimated potential evaporation (mm/month)

${\displaystyle T_{a}}$ is the average daily temperature (degrees Celsius; if this is negative, use ${\displaystyle 0}$) of the month being calculated

• Penman, H.L. (1948). "Natural evaporation from open water, bare soil, and grass". Proc. Roy. Soc. London, U.K. A193 (1032): 120–145. Bibcode:1948RSPSA.193..120P. doi:10.1098/rspa.1948.0037.
• Brutsaert, W.H. (1982). Evaporation into the Atmosphere: theory, history, and applications. Dordrecht, Holland: D. Reidel. ISBN .
• Bonan, Gordon (2002). Ecological Climatology. Cambridge, U.K.: CUP. ISBN .
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