There are roughly two types of methods of observing the movement of substances (flux) between the air and land areas: ground-based observation and satellite observation. In ground-based observation, climate data such as carbon dioxide balances, temperature and precipitation are measured by instruments installed in a flux tower, but ground-based observations cannot cover all areas. In addition to climate data, land cover and vegetation over a wide range of temporal scales can be monitored by satellite observation at high resolution, but it cannot measure carbon balances.

Therefore, model simulation is employed to determine the carbon balance in a wide area. Ground-based data are used to develop models and to conduct validation, and satellite observation data are used to simulate carbon dioxide balances in a wide area.

Fig.1 Model Overview

The BEAMS model (Biosphere model integrating Eco-physiological And Mechanistic approaches using Satellite data, Sasai et al., 2005, 2007) developed by Nagoya University is employed for this calculation. BEAMS was developed to simulate carbon, water and energy processes on the earth surface and their interaction on the basis of ground-based and satellite observational data, and to estimate the amount of exchange and storage.

Spatial data (such as temperature and wind velocity) obtained from ground-based monitoring, satellite observational data (such as precipitation, leaf area index [LAI]), and geographical data (such as vegetation classification, soil classification, soil depth, altitude etc) are used as input data. The estimations of spatial variations of carbon, water and energy fluxes, as well as carbon and water storage in the Far East Asian region from 2001 to 2006 are shown at 1-km grid resolution in monthly time increments.

Fig.2 Model input/output

The carbon, water, and energy processes between air-vegetation-soil are simulated, and each process interacts in the BEAMS model.
In the carbon process, photosynthesis, breathing, withering speed of vegetation and the speed of soil organic matter decomposition are calculated (Fig. 3).
In the water and energy processes, evapotranspiration from vegetation and soil, latent heat and the amount of net radiation are calculated (Fig. 4).
The water and heat stress to vegetation is also calculated simultaneously, and it influences the carbon cycle process as a photosynthesis control factor.

Fig.3 Schematic diagram of carbon cycle process in model
GPP (gross primary production), Ra (autotrophic respiration), LF (litter fall), SD (soil decomposition)

Fig.4 Schematic diagram of the water-energy process in the model
LE (latent heat), Rn (net radiation), H (sensible heat), Inter P. (canopy intercepted precipitation), Inter E. (intercepted evaporation), Evp. (evaporation), Trans. (transpiration), Perc. (percolation) , Gsoil (ground heat flux)

The estimated results of GPP (gross primary production), NEE (net primary production), LE (latent heat), and Rn (net radiation) by the model were validated with flux measurements at six towers around Japan. Since the differences in seasonal patterns and summer peaks etc at every observation point showed a good consistency, it is feasible to use BEAMS to estimate fluxes in a broad area.

Fig. 5 Overview of the Model Validation Process