Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 5 2 2009 10.5194/cpd-5-853-2009 http://www.clim-past-discuss.net/5/853/2009/ http://www.clim-past-discuss.net/5/853/2009/cpd-5-853-2009.html http://www.clim-past-discuss.net/5/853/2009/cpd-5-853-2009.pdf 853 878 2009-03-10 Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa C. Cassignat E. S. Gritti O. Flores R. Bonnefille F. Chalié J. Guiot D. Jolly CEREGE, UMR 6635 CNRS/Aix-Marseille Université, Europôle Méditerranéen de l'Arbois BP80, 13545 Aix en Provence cedex 4, France CEFE, UMR 5175 CNRS/Université Montpellier II, 1919, route de Mende, 34293, Montpellier cedex 5, France ISEM, UMR 5554 CNRS/Université Montpellier II, Case 61, 34095 Montpellier cedex 5, France These authors contributed equally to the work 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. 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