A Coupled Soil-Vegetation Scheme: Description, Parameters, Validation, and, Sensitivity Studies

A coupled soil-vegetation scheme is presented. A one-layer canopy and a three-layer soil representation is used. The impact of canopy morphological properties on radiation and momentum transfer in the vegetation is modeled as simply as possible. The impact of the plant physiology on water transport through the vegetation layer is elaborated on in detail. The canopy resistance is calculated as the product of the fractional relative stomatal conductances of different governing factors. The scheme is tested using point micrometerological and biophysical data. It is shown that the agreement between simulated and measured turbulent fluxes is fairly good. Some sensitivity analyses are also made. The sensitivity of latent and sensible heal flux distribution is investigated with respect to the variations in the leaf drag coefficient Cd, the root density in the soil surface layer Rdes, and various formulations of the relative stomatal conductance for expressing the effect of vegetation moisture availability F(vm). The following main results are obtained. The latent and sensible heat flux distribution above a closed canopy is sensitive to the specific choice of F(vm) and to the variations of Rdes. The sensitivity of turbulent fluxes to Rdes is not as great as that to F(vm) functions. Above sparse canopy the turbulent fluxes are not sensitive to changes to F(vm) and Rdes The latent and sensible heat flux distribution above both closed and sparse canopy is sensitive to the variations of Cd. The variations of Cd affect the turbulent fluxes from the soil surface but have no impact on the transpiration rate. The parameterization of transpiration is already of no importance when the canopy is sparse. The scheme is suitable for the calculation of turbulent fluxes provided that global radiation, cloudiness air temperature, humidity, and wind velocity at screen height are available. It can also be applied in atmospheric models of different scales.