Soil evaporation from sparse natural vegetation estimated from Sherwood numbers
1997
Jacobs, A.F.G. | Verhoef, A.
For various purposes and applications it is convenient to have a simple technique available that produces reliable estimates about the contribution of the soil sensible and latent heat of a crop canopy or natural vegetation to the total fluxes. This is especially of importance in the case of a sparse vegetation where the bare soil is the major component. Under low wind conditions a free convective state often occurs which offers an opportunity to make a simple assessment of the soil sensible heat contribution to the total sensible heat flux. In this case there exists a unique relation between the surface Rayleigh number and the surface Nusselt number. The same technique can be applied to the vapour flux by using a unique relation between the surface Rayleigh number and the surface Sherwood number, if the soil surface is wet. The last condition occurs after a rainy period. Mostly, however, the upper soil layer is dry and the soil evaporation will be limited by the surface resistance to evaporation. If the relation between soil moisture and the so-called 'soil Bowen ratio coefficient', cw, as proposed by Massman (1992) is known, a simple correction to the potential soil evaporation can be applied. During the HAPEX-Sahel experiment the above-mentioned technique has been applied to a natural vegetation under semi-arid conditions. Moreover, the modelled soil evaporation has been verified by micro-lysimeter data. It appeared that the proposed technique is promising and is in agreement with the measurement results.
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