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www.clim-past-discuss.net/5/853/2009/
doi:10.5194/cpd-5-853-2009
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Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa
1CEREGE, UMR 6635 CNRS/Aix-Marseille Université, Europôle Méditerranéen de l'Arbois BP80, 13545 Aix en Provence cedex 4, France
2CEFE, UMR 5175 CNRS/Université Montpellier II, 1919, route de Mende, 34293, Montpellier cedex 5, France
3ISEM, UMR 5554 CNRS/Université Montpellier II, Case 61, 34095 Montpellier cedex 5, France
*These authors contributed equally to the work
Abstract. Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Lake Victoria; Ngamakala, pond, Congo) showed that after 6 ky Before Present (BP), pollen of deciduous trees increase their relative percentage, thus suggesting the beginning of a drier climate and/or an increase of the dry season length. Until now, pollen-climate transfer functions only investigated mean annual precipitation, hence omitting the potential effect of a change in precipitation seasonality. In the present study, we use an equilibrium biosphere model (i.e. BIOME3.5) to estimate the sensitivity of equatorial African vegetation to such changes, at specific sites. Climatic scenarios, differing only by the monthly distribution of the current annual amount of precipitations, are tested at the above three locations in equatorial Africa. Soil nature, monthly temperatures and cloudiness are kept constant at their present day values. A good agreement is shown between model simulations and current biomes assemblages, as reconstructed from pollen data. To date, the increase of the deciduous forest component in the palaeodata around 6 ky has been interpreted as the beginning of the drier climate period. However, our results demonstrate that a seasonal change of the precipitation distribution should likely induce such reconstructed changes toward drier vegetation types. This study confirms the necessity of taking into account seasonal changes in the hydrological balance when palaeoecologists wish to reconstruct vegetation composition or to infer quantitative climate parameters, such as temperature and precipitation, from pollen or vegetation proxy.
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Notice on Discussion StatusCitation: Cassignat, C., Gritti, E. S., Flores, O., Bonnefille, R., Chalié, F., Guiot, J., and Jolly, D.: Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa, Clim. Past Discuss., 5, 853-878, doi:10.5194/cpd-5-853-2009, 2009. Bibtex EndNote Reference Manager XML
