Abstract
The turbulent heat fluxes near the ground surface are strongly affected by the ability of the surface to redistribute the radiative energy absorbed from the sun and the atmosphere into sensible and latent heat. On a bare dry land, the absorption of this energy results in a relatively strong heating of the surface, which usually generates a strong turbulent sensible heat flux in the atmospheric surface layer and a large soil heat flux. In that case, there is no evaporation (i.e., no latent heat flux) and the Bowen ratio (i.e., the ratio of sensible to latent heat flux) is infinite. By contrast, in wet land, as is common in irrigated agricultural areas and/or after rain events, the incoming radiation is mostly used for evaporation. In that case, the turbulent sensible heat flux and the soil heat flux are usually much smaller than the latent heat flux. As a result, the Bowen ratio is close to zero. When the ground is covered by a dense vegetation, water is extracted mostly from the plant root zone by transpiration. Thus, latent heat flux is dominant even if the soil surface is dry, but as long as there is enough water available in the root zone and plants are not under stress conditions.
