Incorporation of CO2 Exchange Processes into a Multilayer Atmosphere–Soil–Vegetation Model

Abstract

Carbon dioxide (CO2) exchange processes were incorporated into a multilayer atmosphere?soil?vegetation model known as SOLVEG, and its performance was examined using measurements obtained from a grassland site. It was also applied for the CO2 budget calculation in the surface ecosystem. The characteristic feature of this model is that it is multilayered for the atmosphere, soil, and vegetation and includes sophisticated processes involving transmission of the solar and longwave radiation fluxes in the canopy. The model framework for the heat and water exchanges between the atmosphere and ground surface was validated by comparisons of ground surface heat fluxes between the calculated and observed values in the previous papers. In this study, a new model framework that includes the exchange process of CO2 along with those of heat, water, and momentum, which interact with each other, has been developed. The performance of the model was examined by comparing the calculated and observed values for surface fluxes of heat, water, and CO2. Because no measurements are available for the direct evaluation of the CO2 calculation in the soil, the calculation has been examined by drawing comparisons between the CO2 fluxes above the ground in the period lacking active vegetation. Vegetation parameters were tuned using measurements of 2 months, and the model satisfactorily simulated measured fluxes for the 8-month-long test period. Moreover, the CO2 budget in the surface ecosystem was examined using the model simulation. The result indicates the necessity of the incorporated CO2 process for the CO2 budget in the surface ecosystem.