Quantitative reconstructions of annual rainfall in Africa 6000 years ago: Model‐data comparison

Peyron, Odile; Jolly, Dominique; Braconnot, Pascale; Bonnefille, Raymonde; Guiot, Joël; Wirrmann, Denis; Chalié, Françoise

doi:10.1029/2006jd007396

Cited by 55 publications

(52 citation statements)

References 61 publications

(94 reference statements)

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“…Our simulations demonstrate that we have to take into account the seasonal distribution of precipitation when reconstructing past climates. Reconstruction of mean annual climatic variables Peyron et al, 2000;Bonnefille and Chalié, 2000;Peyron et al, 2006) in tropical areas must be completed by considering the precipitation seasonal distribution. If BIOME3.5 output correctly matches palaeodata, the next step will consist in developing an objective and automatic procedure to determine which climatic scenario are the most reliable.…”

Section: Discussionmentioning

confidence: 99%

Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

et al. 2010

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Abstract. Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Victoria, lake, Uganda; Ngamakala, pond, Congo) showed that after 6 ky before present (BP), pollen of deciduous trees increase their relative percentage, suggesting thus the reduction of the annual amount of precipitation and/or an increase of in the length of the dry season. Until now, pollen-climate transfer functions only investigated mean annual precipitation, due to the absence of modern pollen-assemblage analogs under diversified precipitation regimes. Hence these functions omit the potential effect of a change in precipitation seasonality modifying thus the length of the dry season. In the present study, we use an equilibrium biosphere model (i.e. BIOME3.5) to estimate the sensitivity of equatorial African vegetation, at specific sites, to such changes. Climatic scenarios, differing only in the monthly distribution of the current annual amount of precipitation, are examined at the above three locations in equatorial Africa. Soil characteristics, monthly temperatures and cloudiness are kept constant at their present-day values. Good agreement is shown between model simulations and current biomes assemblages, as inferred from pollen data. To date, the increase of the deciduous forest component in the palaeodata around 6 ky BP has been interpreted as the beginning of a drier climate period. However, our results demonstrate that a change in the seasonal distribution of precipitation could also induce the observed changes in vegetation types. This study confirms the importance of taking into account seasonal changes in the hydrological balance. Palaeoecologists can greatly benefit from the use of dynamic process based vegetation modCorrespondence to: E. S. Gritti (emmanuel.gritti@cefe.cnrs.fr) els to acccount for modification of the length of the dry season when they 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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Section: Discussionmentioning

confidence: 99%

Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

et al. 2010

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“…For this reason we adopted a multi-method approach that would allow us to better assess reconstruction error and provide more precise and robust climate estimates than those based on only one method (e.g. Klotz et al, 2003;Peyron et al, 2005Peyron et al, , 2006Kühl et al, 2010). Such an approach has been successfully tested for the Holocene from Mediterranean marine and terrestrial pollen records Peyron et al, 2011, although see Birks et al, 2010.…”

Section: Climate Reconstruction Methodsmentioning

confidence: 99%

Contrasting patterns of climatic changes during the Holocene across the Italian Peninsula reconstructed from pollen data

et al. 2013

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Lake-level records from Italy suggest that patterns of precipitation in the central Mediterranean during the Holocene were divided between the north and south, but a scarcity of reliable palaeoclimatic records in the north and central-southern Mediterranean means new evidence is needed to validate this hypothesis. We provide robust quantitative estimates of Holocene climate in the Mediterranean region using four high-resolution pollen records from northern (Lakes Ledro and Accesa) and southern (Lakes Trifoglietti and Pergusa) Italy. Multiple methods are used to provide an improved assessment of the palaeoclimatic reconstruction uncertainty. The multi-method approach uses the pollenbased weighted averaging, weighted-average partial leastsquares regression, modern analogue technique, and the nonmetric multidimensional scaling/generalized additive model methods. We use independent lake-level data to validate the precipitation reconstructions. Our results support a climatic partition between northern and southern Italy during the Holocene, confirming the hypothesis of opposing mid-Holocene summer precipitation regimes in the Mediterranean. The northern sites (Ledro, Accesa) are characterized by minima for summer precipitation and lake levels during the early to midHolocene, while the southern sites (Trifoglietti, Pergusa) are marked by maxima for precipitation and lake levels at the same time. Both pollen-inferred precipitation and lake levels indicate the opposite pattern during the late Holocene, a maximum in northern Italy and a minimum in southern Italy/Sicily. Summer temperatures show the same partitioning, with warm conditions in northern Italy and cool conditions in Sicily during the early/mid-Holocene, and a reversal during the late Holocene. Comparison with marine cores from the Aegean Sea suggests that climate trends and gradients observed in Italy show strong similarities with those recognized from the Aegean Sea, and more generally speaking in the eastern Mediterranean

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“…), paleoclimate proxy data consistently show a northward extension of grass and low-shrubs into the Sahel/Sahara region (Jolly et al 1998;Gasse 2000;Prentice and Jolly 2000;Peyron et al 2006;Garcin et al 2007) that was accompanied by significant changes of the hydrological conditions over northern Africa (Overpeck et al 1996;deMenocal et al 2000;Morrill et al 2003;Fleitmann et al 2003;Peck et al 2004; Shanahan et al 2006;Weldeab et al 2007;Fleitmann et al 2007). While numerous paleoproxy (e.g.…”

Section: Introductionmentioning

confidence: 95%

Mechanisms for the Onset of the African Humid Period and Sahara Greening 14.5–11 ka BP*

et al. 2010

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The mechanisms leading to the onset of the African Humid Period (AHP) 14,500 to 11,000 years ago are elucidated using two different climate-vegetation models in a suite of transient glacialinterglacial simulations covering the last 21,000 years. A series of sensitivity experiments investigated three key mechanisms (local summer insolation and ice sheet evolution, vegetationalbedo-precipitation feedback, CO 2 increase via radiative forcing and fertilization) that control the climate-vegetation history over North Africa during the last glacial termination. The simulations showed that neither orbital forcing nor the remote forcing from the retreating ice-sheets alone were able to trigger the rapid formation of the AHP. Only both forcing factors together can effectively lead to the formation of the AHP. The vegetation-albedo-precipitation feedback enhances the intensity of the monsoon and further accelerates the onset of the AHP. The experiments indicate that orbital forcing and vegetation-albedo-precipitation feedback alone are insufficient to trigger the rapid onset of the AHP. The sensitivity experiments further show that the increasing radiative forcing from rising CO 2 concentrations had no significant impact on the temporal evolution of the African monsoon during the last deglaciation. However, the fertilization effect of CO 2 is important for the terrestrial carbon storage. The modeling results are discussed and compared with paleo proxy records of the African monsoon system. It is concluded that the model results presented here do not lend support to the notion that simple insolation thresholds govern the abrupt transitions of North African vegetation during the early to middle Holocene.1

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Quantitative reconstructions of annual rainfall in Africa 6000 years ago: Model‐data comparison

Cited by 55 publications

References 61 publications

Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

Contrasting patterns of climatic changes during the Holocene across the Italian Peninsula reconstructed from pollen data

Mechanisms for the Onset of the African Humid Period and Sahara Greening 14.5–11 ka BP*

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