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Variability and recent trends in the African carbon balance
P. Ciais1, S.-L. Piao2, P. Cadule1, P. Friedlingstein1, and A. Chédin3
1LSCE, UMR CEA-CNRS, CE, L'Orme des Merisiers, Gif-sur-Yvette, France
2Department of Ecology, College of Urban and Environmental Sciences, Peking University, Beijing, China
3Groupe Analyse du Rayonnement Atmospherique, Laboratoire de Meteorologie Dynamique, Institut Pierre Simon Laplace, ARA/LMD/IPSL, Ecole Polytechnique RD 36, Palaiseau, France
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Abstract. We modeled the African carbon balance over the past century using the
process based ORCHIDEE model, forced by changing climate and human induced
changes in land use. The model includes a simple parameterization of natural
fires, but the natural vegetation dynamics was ignored. The period analyzed
is 1901–2002. Overall, we found that the African net carbon balance (Net
Biome Productivity, NBP) increased from a net carbon source of −0.14 Pg C yr−1
in the 1980s to a net carbon sink of 0.15 Pg C yr−1 in the 1990s.
Deforestation is estimated to be a source of 0.13 Pg C yr−1, implying a
compensating effect of climate trends (mainly increasing precipitation) plus
CO2 fertilization, causing a sink of 0.28 Pg C yr−1. We found that
the interannual variability of NBP is mostly driven by photosynthesis
changes. Over savannas, photosynthesis changes from one year to the next are
strongly correlated with rainfall changes (R2=0.77 in northern
Africa, and R2=0.42 in southern African savannas). Over forests, such
a control by rainfall is not found. The main spatial pattern of interannual
variability in NBP and in gross carbon fluxes is related with ENSO, with
dryer conditions prevailing over savannas during El Niño and wetter
conditions over forests. Climate induced variations in fire emissions
respond to this ENSO forcing, but they do not determine strongly the NBP
variations. Finally, we model that ecosystem respiration variations (mostly
due to autotrophic respiration) are tailing with those of photosynthesis, on
interannual as well as on decadal time scales, but this result is uncertain
given the potential for acclimation for autotrophic respiration processes.
Discussion Paper (PDF, 1488 KB) Interactive Discussion (Closed, 3 Comments) Final Revised Paper (BG)
Citation: Ciais, P., Piao, S.-L., Cadule, P., Friedlingstein, P., and Chédin, A.: Variability and recent trends in the African carbon balance, Biogeosciences Discuss., 5, 3497-3532, 2008. Bibtex EndNote Reference Manager
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