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Rainfall and drought in equatorial east Africa during the past 1,100 years

Abstract

Knowledge of natural long-term rainfall variability is essential for water-resource and land-use management in sub-humid regions of the world. In tropical Africa, data relevant to determining this variability are scarce because of the lack of long instrumental climate records and the limited potential of standard high-resolution proxy records such as tree rings and ice cores1,2,3. Here we present a decade-scale reconstruction of rainfall and drought in equatorial east Africa over the past 1,100 years, based on lake-level and salinity fluctuations of Lake Naivasha (Kenya) inferred from three different palaeolimnological proxies: sediment stratigraphy and the species compositions of fossil diatom and midge assemblages. Our data indicate that, over the past millennium, equatorial east Africa has alternated between contrasting climate conditions, with significantly drier climate than today during the ‘Medieval Warm Period’ ( ad 1000–1270) and a relatively wet climate during the ‘Little Ice Age’ ( ad 1270–1850) which was interrupted by three prolonged dry episodes. We also find strong chronological links between the reconstructed history of natural long-term rainfall variation and the pre-colonial cultural history of east Africa4, highlighting the importance of a detailed knowledge of natural long-term rainfall fluctuations for sustainable socio-economic development.

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Figure 1: Sedimentological and biological evidence for past lake-depth and salinity fluctuations in the Crescent Island Crater basin of Lake Naivasha.
Figure 2: Comparison of Crescent Island Crater history with documented and reconstructed climate-proxy data.

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Acknowledgements

We thank K. Mavuti, B. Ammann, F. Janssen and H. E. Wright for field assistance; the Lake Naivasha Riparian Association for lake access; F. Gasse for use of the African diatom reference and calibration data sets; and S. Fritz, F. Gasse, K. Kelts, F. Oldfield, J. P. Smol, B. Tinsley and H. E. Wright for comments on the manuscript. This work was supported by NSF, the Quaternary Paleoecology Program at the University of Minnesota, and by fellowships from NOAA and FWO-Vlaanderen (D.V.) The fieldwork was conducted with permission from the Office of the President of the Republic of Kenya to K. Mavuti.

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Correspondence to Dirk Verschuren.

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The data presented here are archived at the World Data Center-A for Paleoclimatology.

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Figure 1

Fossil diatom taxa in the sediment record of Crescent Island Crater (Lake Naivasha, Kenya) (DOC 783 kb)

Figure 2

Fossil chironomid taxa in the sediment record of Crescent Island Crater (Lake Naivasha, Kenya) (DOC 764 kb)

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Verschuren, D., Laird, K. & Cumming, B. Rainfall and drought in equatorial east Africa during the past 1,100 years. Nature 403, 410–414 (2000). https://doi.org/10.1038/35000179

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