Using remote sensing and in situ network observations to evaluate and improve the performance of the Biome-BGC terrestrial carbon cycle model at regional and global scales

Summary

Our primary goal is to evaluate and improve the ability of the Biome-BGC model to represent the seasonal, interannual, and multi-decadal dynamics of the terrestrial carbon system, which control net ecosystem exchange of carbon (NEE) with the atmosphere. This requires close examination of the processes contributing to NEE: gross photosynthesis, autotrophic (plant) respiration, and heterotrophic respiration (decomposition by microorganisms), and the environmental controls on these processes. We are particularly concerned with terrestrial carbon cycle dynamics that have important interactions with the atmosphere through the surface energy and hydrologic budgets, and with the effects of disturbance history on these interactions. We are using a series of focused investigations to evaluate and improve model components that we have previously identified as critical determinants of terrestrial NEE. In parallel with these detailed process studies, we are producing a global model implementation and analysis designed to assess model behavior as integrated by daily carbon cycle flux components. We focus our efforts in the project on model components and outputs that are especially conducive to study using an innovative combination of remote sensing observations and in situ network observations.

These advances should improve our ability to predict future terrestrial carbon cycle dynamics, especially as they relate to potential future changes in climate, atmospheric chemistry, and land management practices. Objectives 1 (improved phenology) and 2 (improved surface resistance parameterization) are critical to the community-wide effort to link terrestrial and atmospheric components as complete carbon system models. Objective 3 (investigation of disturbance effects) is a necessary step in identifying and explaining the spatial and temporal patterns of terrestrial sources and sinks of carbon. Objective 4 will be pursued in collaboration with researchers at Scripps Institute of Oceanography, providing additional constraints on the seasonal cycle and interannual variability of NEE at the global scale and over coarse latitudinal and longitudinal zones. Improvements to the model identified under Objectives 1-3 will be tested at the global scale under Objective 4. We have already made substantial progress toward each of these objectives, and we expect that these new investigations will result in a measurably improved description of important processes in the Biome-BGC model.