East African aridification during the past 8 million years is frequently invoked as a driver of large-scale shifts in vegetation1 and the evolution of new animal lineages, including hominins2,3,4. However, evidence for increasing aridity is debated5 and, crucially, the mechanisms leading to dry conditions are unclear6. Here, numerical model experiments show that valleys punctuating the 6,000-km-long East African Rift System (EARS) are central to the development of dry conditions in East Africa. These valleys, including the Turkana Basin in Kenya, cause East Africa to dry by channelling water vapour towards Central Africa, a process that simultaneously enhances rainfall in the Congo Basin rainforest. Without the valleys, the uplift of the rift system leads to a wetter climate in East Africa and a drier climate in the Congo Basin. Results from climate model experiments demonstrate that the detailed tectonic development of Africa has shaped the rainfall distribution, with profound implications for the evolution of African plant and animal lineages.
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Model data arising from this paper used in plotting and the edited high-resolution GLOBE dataset orography files for each experiment are available on publication at https://doi.org/10.5281/zenodo.6956995. ERA5 data were downloaded from https://cds.climate.copernicus.eu/cdsapp#!/home. CHIRPS data are available at https://data.chc.ucsb.edu/products/CHIRPS-2.0/. GPCP data are from https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00979. Data used in base maps for figures are publicly available from https://www.naturalearthdata.com/ and plotted with Cartopy (https://github.com/SciTools/cartopy/archive/v0.11.2.tar.gz). The UK Met Office Unified Model is available for use under license. For further information on how to apply for a license, see http://www.metoffice.gov.uk/research/modelling-systems/unified-model.
Code for producing figures is available on publication at https://doi.org/10.5281/zenodo.6956995.
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We acknowledge the input from and useful discussions with J. Lee-Thorp and R. Bobé (both Oxford University). This article is an output from the REACH programme, financed by UK Aid from the UK Foreign, Commonwealth and Development Office (FCDO) for the benefit of developing countries (programme code 201880). However, the views expressed and information contained in it are not necessarily those of or endorsed by the FCDO, which can accept no responsibility for such views or information or for any reliance placed on them.
The authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Water vapour transport in control and reanalysis data.
The arrows show the direction and strength at which atmospheric-column integrated water vapour is being transported (kg m−1 s−1) in the control experiment (a) and ERA5 (b). Shading gives the IWVT magnitude (kg m−1 s−1) (see Methods). The East African region we use to evaluate the moisture budget is bounded by the red line in a. ERA5 data42 are available at https://cds.climate.copernicus.eu/cdsapp#!/home.
Extended Data Fig. 2 Evaluation of rainfall in the control simulation.
Annual rainfall (mm year−1) in the control (a), CHIRPS (b) and GPCP version 2.2 (c). CHIRPS38 data are available at https://data.chc.ucsb.edu/products/CHIRPS-2.0/. GPCP data39 are from https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00979.
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Munday, C., Savage, N., Jones, R.G. et al. Valley formation aridifies East Africa and elevates Congo Basin rainfall. Nature 615, 276–279 (2023). https://doi.org/10.1038/s41586-022-05662-5
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