A biosphere-atmosphere interaction model (BAIM) and its primary verifications using grassland data

A Biosphere-Atmosphere Interaction Model (BAIM) for use within physical climate models was developed. BAIM has two vegetation layers and three soil layers, and predicts the temperature of each layer and moisture stored for each layer. In the presence of snow on the ground, the snow layer is divided into a maximum of three layers, and the temperature and the amount of snow and water stored in each layer are predicted. BAIM can estimate not only the energy fluxes but also the carbon dioxide flux between the land surface ecosystem and the atmosphere. The photosynthesis processes for C3 plants and C4 plants are adopted in the model. BAIM can also predict the accumulation and melting of snow on the ground, and the freezing and melting of water in the soil.   Primary off-line verifications of BAIM in a snowless condition were made using point micrometeorological data observed at grassland. In general, fluxes simulated by the model agreed well with those observed. In particular, clear differences between results using the parameters for C3 plants and those using the parameters for C4 plants appeared in the net carbon dioxide fluxes.   Sensitivity tests were conducted for the model to study the influence of variations in the values of parameters related to the property of vegetation. By changing the values of the parameters by ±50%, the maximum variations in the time-averaged fluxes were obtained. The values for net radiation flux, sensible heat flux, latent heat flux, and soil heat flux were about ±15W m-2, ±8W m-2, ±9W m-2, and ±1W m-2, respectively. The maximum variations in the time-averaged value of net carbon dioxide flux were about±5μmol m-2 s-1 for C3 parameters and±7μmol m-2 s-1 for C4 parameters. These maximum variation values are comparable to observation errors.