The North American Carbon Program Multi-Scale Synthesis and Terrestrial Model Intercomparison Project – Part 1: Overview and experimental design
D.N. Huntzinger, C. Schwalm, A.M. Michalak, K. Schaefer, A.W. King, Y. Wei, A. Jacobson, S. Liu, R.B. Cook, W.M. Post, G. Berthier, D. Hayes, M. Huang, A. Ito, H. Lei, C. Lu, J. Mao, C.H. Peng, S. Peng, B. Poulter, D. Riccuito, X. Shi, H. Tian, W. Wang, N. Zeng, F. Zhao and Q. Zhu
Terrestrial biosphere models are often used to represent the land-atmosphere exchange of carbon at regional to global scales, but estimates vary greatly across existing models. These differences stem from specific choices in environmental driver data used to run the models, how the models are spun-up and run, as well as structural differences in how individual models represent biospheric processes. The Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP) is designed to isolate the impact of model structural differences, by prescribing a detailed protocol that all participating models follow. This manuscript gives an overview of this protocol and initial results.
Terrestrial biosphere models (TBMs) have become an integral tool for extrapolating local observations and understanding of land–atmosphere carbon exchange to larger regions. The North American Carbon Program (NACP) Multi-scale synthesis and Terrestrial Model Intercomparison Project (MsTMIP) is a formal model intercomparison and evaluation effort focused on improving the diagnosis and attribution of carbon exchange at regional and global scales. MsTMIP builds upon current and past synthesis activities, and has a unique framework designed to isolate, interpret, and inform understanding of how model structural differences impact estimates of carbon uptake and release. Here we provide an overview of the MsTMIP effort and describe how the MsTMIP experimental design enables the assessment and quantification of TBM structural uncertainty. Model structure refers to the types of processes considered (e.g., nutrient cycling, disturbance, lateral transport of carbon), and how these processes are represented (e.g., photosynthetic formulation, temperature sensitivity, respiration) in the models. By prescribing a common experimental protocol with standard spin-up procedures and driver data sets, we isolate any biases and variability in TBM estimates of regional and global carbon budgets resulting from differences in the models themselves (i.e., model structure) and model-specific parameter values. An initial intercomparison of model structural differences is represented using hierarchical cluster diagrams (a.k.a. dendrograms), which highlight similarities and differences in how models account for carbon cycle, vegetation, energy, and nitrogen cycle dynamics. We show that, despite the standardized protocol used to derive initial conditions, models show a high degree of variation for GPP, total living biomass, and total soil carbon, underscoring the influence of differences in model structure and parameterization on model estimates.
Huntzinger, D.N., C. Schwalm, A.M. Michalak, K. Schaefer, A.W. King, Y. Wei, A. Jacobson, S. Liu, R.B. Cook, W.M. Post, G. Berthier, D. Hayes, M. Huang, A. Ito, H. Lei, C. Lu, J. Mao, C.H. Peng, S. Peng, B. Poulter, D. Riccuito, X. Shi, H. Tian, W. Wang, N. Zeng, F. Zhao, Q. Zhu (2013) "The North American Carbon Program Multi-Scale Synthesis and Terrestrial Model Intercomparison Project – Part 1: Overview and experimental design", Geoscientific Model Development, 6, 2121-2133, doi:10.5194/gmd-6-2121-2013.