ABSTRACT
Evaporation begins with the movement of molecules of water. Inside a mass of liquid water, the molecules vibrate and circulate in random fashion. This movement is related to the temperature: the higher the temperature, the more the movement is amplified and the more energy there is to allow the molecules to escape and enter the atmosphere. After studying this process, Dalton (1802) put forward a law that expresses the rate of evaporation from a waterbody as a function of a deficit in the saturation of the air (a quantity of water eS – ea that the air can store expressed in pascal[Pa], millibars [mb] or millimeters of mercury [mm Hg]) and a wind speed u. This law is expressed:
(5.2)
where E is the rate of evaporation (or evaporation flux) ea is the effective or actual
vapor pressure of water in the air, es is the saturated water vapor pressure at the temperature of the evaporating surface, and f(u) is a proportionality constant for the wind speed u.
