Above-belowground Carbon Allocation in Earth System Models

Tuesday, 16 December 2014
Xia Song1, Forrest M Hoffman2, Xiaofeng Xu1, Colleen M. Iversen3 and Jitendra Kumar3, (1)University of Texas at El Paso, El Paso, TX, United States, (2)University of California Irvine, Department of Earth System Science, Irvine, CA, United States, (3)Oak Ridge National Laboratory, Oak Ridge, TN, United States
Above-belowground carbon allocation is a critical mechanism for vegetation growth and its adaptation to the changing environment. The model representation of carbon allocation mechanisms significantly influence the simulated carbon stock and land-atmosphere exchange in Earth System Models (ESMs). Few previous studies, however, have investigated and evaluated the above-belowground carbon allocation in ESMs. In this study, we analyzed carbon density in belowground, total vegetation (above + belowground), and belowground:vegetation ratios of eleven ESMs from the Coupled Model Inter-comparison Project Phase 5 (CMIP5), which were used for the latest IPCC Assessment Report (AR5).

Overall, results of ESMs are not consistent with observational data; both the belowground and total vegetation carbon density are underestimated in tropical/subtropical and temperate regions, while overestimated in arctic/subarctic regions. Moreover, the ratios of belowground:total vegetation carbon are underestimated in all three climate zones. The model-data discrepancies in carbon density vary substantially among biomes, while the ratios of belowground:total vegetation carbon are consistently underestimated across all major biomes expect tropical moist forests. This study indicates that the carbon allocation algorithms in current ESMs need to be improved to better simulate vegetation growth and its responses to global change.