Transport processes in the soil-vegetation-lower atmosphere system
The interaction of the land surface and the atmosphere may be summarised as follows: interaction of vegetation with radiation, evaporation from bare soil, evapotranspiration which includes transpiration and evaporation of intercepted precipitation and dew, conduction of soil water through the vegetation layer, vertical movement water in the soil, run-off, heat conduction in the soil, momentum transport, effects of snow presence and freezing or melting of soil moisture. Consequently, the processes parametrized in the land surface schemes can be divided into three parts: thermal and hydraulic processes, bare soil transfer processes and canopy transport processes. The chapter shortly describes these processes through a land surface scheme capturing the main processes in the soil-vegetation-lower atmosphere system. The biophysical processes in vegetation are elaborated using so-called “sandwich” representation where the vegetation is treated as a block of constant-density porous material “sandwiched” between two constant-stress layers with an upper boundary (the height of the canopy top) and a lower boundary (the height of the canopy bottom). For description of the transport processes in the soil, the three-soil layer approach is used. The chapter also includes a detailed description and explanation of governing equations, the representation of energy fluxes and radiation, the parameterization of aerodynamic characteristics, resistances and model hydrology. A special attention will be devoted to consideration of “K”- theory within and above canopy.