Estimation of wet surface evaporation from sensible heat flux measurements

A new method is proposed to estimate wet surface evaporation by means of measurements of sensible heat flux and of air temperature, relative humidity, and wind speed at one level only. This formulation is made possible by the linearization of the Bowen ratio, a common assumption in other methods, such as Penman’s model and its derivatives. The method will be useful in those cases where the sensible heat flux is more reliably acquired at field scales than the net radiation and the ground heat flux, which are needed in many operational methods because of energy budget considerations. Indeed, the ground heat flux is a notoriously difficult variable to measure on wet surfaces, such as lakes or wetlands, especially at the appropriate length scales, whereas sensible heat flux can be obtained from standard temperature variance methods or other instruments such as scintillometers. The proposed method was tested with field experimental data taken over Lake Geneva in Switzerland, where it showed excellent agreement with evaporation rates measured using eddy covariance techniques.