A biosphere model based on the Biosphere Atmosphere Transfer Scheme (BATS) suitable for coupling with a simple climate model is described. In this model the equations of BATS are adapted to the energy flux formulations of the statistical-dynamical model developed by Franchito & Rao (Climatic Change, 22:1-34; 1992). In this work the land surface model was run to perfom sensitivity tests regarding the behaviour of the model variables with respect to prescribed model parameters and contrasting vegetation types, such as evergreen broadleaf forest and short grass. The results show that the soil surface temperature increases with the decrease of the fractional area of vegetation cover due to the lower surface solar radiation flux absorption in both types of vegetation. As the water interception increases the wet foliage air layer prevents the evaporation of the soil water, so that there is an increase of the ground surface temperature. The surface temperature is lower in the forest than in the case of short grass due to the surface roughness effect. In the case of dry soil the available energy increases with the increase of the fractional area of vegetation cover because the latent heat flux increases quickly and the sensible heat flux decreases slowly. In the situation of fully wet soil the available energy dependence on the interception is reduced due to the effect of water evaporation at the ground surface that increases the latent heat flux, even if the interception is small or nil. A factor <FONT FACE="Symbol">z</font> is inserted in the expression that gives the fractional area of the leaf canopy cover by water in order to take into account the effect of the part of vegetation predominantly porous. The lower values of <FONT FACE="Symbol">z </font>give better results regarding the component terms of the evapotranspiration. However, the total flux of water vapor to atmosphere does not change with <FONT FACE="Symbol">z</font>. Sensitivity tests are made with respect to the factor Y introduced in the expression of the water vapor flux to the atmosphere in order to adjust the partitioning of the available energy into latent and sensible heat. The results show that the latent (sensible) heat increases (decreases) with the increase in Y. Although the variation of Y modifies the Bowen’s ratio there is no change of the evapotranspiration partitioning into its components.
Biosphere model based on BATS; Statistical-dynamical model; Sensitivity tests with a biosphere model
