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Multidecadal variability in East African hydroclimate controlled by the Indian Ocean

Nature volume 493, pages 389–392 (2013)Cite this article

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Abstract

The recent decades-long decline in East African rainfall1 suggests that multidecadal variability is an important component of the climate of this vulnerable region. Prior work based on analysing the instrumental record implicates both Indian2 and Pacific1 ocean sea surface temperatures (SSTs) as possible drivers of East African multidecadal climate variability, but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms. Here we show that on timescales beyond the decadal, the Indian Ocean drives East African rainfall variability by altering the local Walker circulation, whereas the influence of the Pacific Ocean is minimal. Our results, based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models, reveal that moist conditions in coastal East Africa are associated with cool SSTs (and related descending circulation) in the eastern Indian Ocean and ascending circulation over East Africa. The most prominent event identified in the proxy record—a coastal pluvial from 1680 to 1765—occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium. Taken together, the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales.

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Figure 1: Results of the MCEOF proxy synthesis.
Figure 2: Field correlations between simulated East African precipitation and SSTs.
Figure 3: Field correlations between simulated East African precipitation and vertical velocity.
Figure 4: Comparison between East Africa MCEOF1 (blue) and an SST reconstruction from the Makassar strait in the western Pacific warm pool (orange)17.

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Acknowledgements

J.E.T. acknowledges the US NOAA Climate and Global Change Postdoctoral Fellowship and NSF OCE-1203892 for support. J.E.S. and R.S. were supported by the NOAA award Global Decadal Hydroclimate Variability and Change (NA10OAR431037). We thank the National Center for Atmospheric Research, who made the CCSM4 control simulation available through the US Earth System Grid (ESG) Center. Support for the ESG is provided by the Office of Science, US Department of Energy, with co-sponsorship from the US NSF. Thanks also to NOAA GFDL for providing the multimillennial control simulation output from the GFDL CM2.1 model, to N. Naik for her on-site support at LDEO and to J. Jungclaus of the Max Planck Institute for providing output from the MPI COSMOS control simulation. This is LDEO contribution number 7641.

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Authors and Affiliations

  1. Woods Hole Oceanographic Institution, Woods Hole, 02543, Massachusetts, USA

    Jessica E. Tierney & Kevin J. Anchukaitis

  2. Lamont-Doherty Earth Observatory of Columbia University, Palisades, 10964, New York, USA

    Jessica E. Tierney, Jason E. Smerdon, Kevin J. Anchukaitis & Richard Seager

Authors
  1. Jessica E. Tierney
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Contributions

J.E.T. designed the study and interpreted the palaeoclimate results. J.E.S. provided the climate modelling results. K.J.A. and J.E.T. designed and implemented the MCEOF method. J.E.S. and R.S. interpreted the dynamical implications of the climate model output. All authors collaborated on the synthesis of the proxy and model data and the writing of the manuscript.

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Correspondence to Jessica E. Tierney.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text 1-4, Supplementary References, Supplementary Tables 1- 2, and Supplementary Figures 1-6. (PDF 3796 kb)

Supplementary Data

This file contains the proxy data used in the East African synthesis. It includes the associated chronological information and the MCEOF1 time series and spatial loadings. (XLS 325 kb)

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Tierney, J., Smerdon, J., Anchukaitis, K. et al. Multidecadal variability in East African hydroclimate controlled by the Indian Ocean. Nature 493, 389–392 (2013). https://doi.org/10.1038/nature11785

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