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Leaf Area and Land Cover Output of CMIP5 Earth System Models

Paper Reviewed
Bao, Y., Gao, Y., Lu, S., Wang, Q., Zhang, S., Xu, J., Li, R., Li, S., Ma, D., Meng, X., Chen, H. and Chang, Y. 2014. Evaluation of CMIP5 earth system models in reproducing leaf area index and vegetation cover over the Tibetan Plateau. Journal of Meteorological Research 28: 1041-1060.

In setting the stage for their study, Bao et al. (2014) write that "in a modeling system changes in vegetation biomass and coverage affect the simulated climate in future climate projections through biophysical and biogeochemical effects," while noting that "in the Earth system models (ESMs) as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5), a dynamic global vegetation model (DGVM) is often included, which calculates interactive vegetation variation (biomass and coverage) due to climate change simulated by the atmospheric model component," citing the work of Collins et al. (2011) and Watanabe et al. (2011). But they further note in this regard that "since DGVMs are driven by atmospheric models, and simulated biases inevitably exist in these atmospheric components, the subsequent simulations of vegetation dynamics are also far from perfect," which fact they then proceed to demonstrate for us.

As described in their paper's abstract, the 12 Chinese researchers assessed the abilities of a dozen ESMs from the CMIP5 program "to reproduce satellite-derived vegetation biological variables over the Tibetan Plateau (TP)." And in doing so, they discovered a number of ways in which the models failed to produce that which they had hoped to have them do.

Very briefly, Bao et al. found that "most of the models tend to [1] overestimate the observed leaf area index (LAI) and [2] vegetation carbon above ground, with the possible reasons being [3] overestimation of photosynthesis and [4] precipitation." In addition, they say that the models (5) "fail to reproduce the downward trend around the headstream of the Yellow River shown in the observations due to their [6] coarse resolutions," while also noting that the model ensemble (7) "overestimated land coverage" and (8) "underestimated tree fraction."

And so it was that the models experienced what Bao et al. describe as "bad performance in reproducing the mean values of observed [9] leaf area index and [10] net primary production," which results seem to be about par for the course of new climate model developments nowadays.

Collins, W., Bellouin, N., Doutriaux-Boucher, M., Gedney, N., Halloran, P., Hinton, T., Hughes, J., Jones, C.D., Joshi, M., Liddicoat, S., Martin, G., O'Connor, F., Rae, J., Senior, C., Sitch, S., Totterdell, I., Wiltshire, A. and Woodward, S. 2011. Development and evaluation of an earth-system model - HadGEM2. Geoscientific Model Development Discussions 4: 997-1062.

Watanabe, S., Hajima, T., Sudo, K., Nagashima, T., Takemura, T., Okajima, H., Nozawa, T., Kawase, H., Abe, M., Yokohata, T., Ise, T., Sato, H., Kato1, E., Takata, K., Emori1, S. and Kawamiya, M. 2011. MIROC-ESM: Model description and basic results of CMIP5-20c3m experiments. Geoscientific Model Development Discussions 4: 1063-1128.

Posted 12 May 2015