Land-Atmosphere interactions for climate system Models: coupling biophysical, biogeochemical, and ecosystem dynamical processes

The biogeographical distribution of different vegetation types and the physiological status of vegetation are significant controls of energy, water, and C02 exchanges between land surfaces and the atmosphere. These exchanges affect local, regional, and global climates, which feedback to affect the biogeography and physiology of the vegetation. Consequently, there is interest in developing a comprehensive land surface scheme that integrates bio-physical, biogeochernical, and ecosystem dynamical processes. Land surface process models of energy and moisture exchanges, ecosystem biogeochemistry models, and ecosystem dynamics models share many features. However, these models have been developed independently by groups interested in their respective field not in the integration across fields. Thus, there are important discrepancies among models that will have to be reconciled if an integrative land-atmosphere interaction package is to be developed. In particular, the temporal resolution and biophysical rigor of land surface process models and the links among energy, water, and C02 exchange make these models the logical model to calculate land-atmosphere CO2 exchange at diurnal to annual time scales. Longer-term exchanges can be simulated by including plant demography and nutrient cycling. Models that combine the biophysical and biogeochemical controls of C02 exchange help define remote sensing applications important to modeling the seasonal and annual carbon balance of terrestrial ecosystems. Sensitivity analyses with such a model show that the annual production of biomass and the seasonal cycle of C02 exchange in boreal forests are well approximated merely by knowing the beginning and end of the growing season, absorbed photosynthetically active radiation, foliage nitrogen concentration, and vegetation type.