Evaporation from a Drying Soil.

A combination formula for evaporation that uses the surface temperature measured by infrared thermometers as a boundary condition is successfully tested against the evaporation obtained from a detailed energy balance and Bowen ratio measurements. The transfer coefficients used in the combination formula are obtained from aerodynamic similarity and include the effect of the diabatic turbulence. Two simple resistive models which attempt to account for the reduction of evaporation due to the water vapor desaturation of the soil surface are analyzed, but fail to describe correctly the transfer processes through the dry upper layer of the soil.