CP Climate of the Past CP Clim. Past 1814-9332 Copernicus Publications Göttingen, Germany 10.5194/cp-7-1351-2011 Late Holocene plant and climate evolution at Lake Yoa, northern Chad: pollen data and climate simulations Lézine A.-M. 1 Zheng W. 2 Braconnot P. 1 Krinner G. 3 Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CNRS-CEA-UVSQ, Orme des Merisiers, Bâtiment 701, 91191 Gif-sur-Yvette cedex, France LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, P.O. Box 9804, 100029 Beijing, China Laboratoire de Glaciologie et Géophysique de l'Environnement, UMR5183, CNRS-UJF Grenoble, Domaine Universitaire, 54 Rue Molière, BP 96, 38402 St Martin d'Hères cedex, France 09 12 2011 7 4 1351 1362 Copyright: © 2011 A.-M. Lézine et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://cp.copernicus.org/articles/7/1351/2011/cp-7-1351-2011.html The full text article is available as a PDF file from https://cp.copernicus.org/articles/7/1351/2011/cp-7-1351-2011.pdf

The discovery of groundwater-fed Lake Yoa (19.03° N, 20.31° E) in the hyperarid desert of northern Chad by the German research team ACACIA headed by S. Kröpelin provides a unique, continuous sedimentary sequence of late Holocene age available in the entire Saharan desert. Here we present pollen data and climate simulations using the LMDZ atmospheric model with a module representing the climatologically-relevant thermal and hydrological processes occurring above and beneath inland water surfaces to document past environmental and climate changes during the last 6000 cal yr BP. Special attention is paid to wind strength and direction, length and amplitude of the rainy season, and dry spell occurrence, all of which are of primary importance for plant distribution and pollen transport. In addition to climate changes and their impact on the natural environment, anthropogenic changes are also discussed. Two main features can be highlighted: (1) the shift from an earlier predominantly monsoonal climate regime to one dominated by northern Mediterranean fluxes that occurred after 4000 cal yr BP. The direct consequence of this was the establishment of the modern desert environment at Yoa at 2700 cal yr BP. (2) Changes in climate parameters (simulated rainfall amount and dry spell length) between 6 and 4000 cal yr BP were comparatively minor. However, changes in the seasonal distribution of precipitation during this time interval dramatically affected the vegetation composition and were at the origin of the retreat of tropical plant communities from Lake Yoa.

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