The influence of the spatial heterogeneity of vegetation cover and surface topography on vertical CO2 fluxes within the atmospheric surface layer

The influence of the spatial heterogeneity of vegetation cover and topography on CO2 fluxes in the atmospheric surface layer is estimated using a two-dimensional (2D) hydrodynamic model of turbulent exchange. A similar to 4.5-km-long profile that crossed a hilly area with a mosaic vegetation cover in Tula region was selected for model experiments. During the first experiment, a wind field and vertical fluxes were calculated by the 2D model for the entire selected profile with respect to the horizontal heterogeneity of the vegetation cover and surface topography. In the second experiment, the profile was considered an assemblage of elementary independent homogeneous segments; for each of them, vertical fluxes were calculated by the 2D model with the assumption of 'zero' horizontal advection, i.e., the required functions are independent of the horizontal coordinates. The influences of any boundary effects that appear at the interface between the different vegetation communities and at topographical irregularities on the turbulent regime are ignored in this case. For the profile selected, ignoring the horizontal advection, disturbances in the wind field that appeared at surface topography irregularities, and boundaries between different vegetation communities can lead to a 26% underestimation of the total CD2 absorption by the ground surface on a clear sunny day under summer weather conditions.