Letter

Frequency of extreme Sahelian storms tripled since 1982 in satellite observations

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Accepted:
Published online:

Abstract

The hydrological cycle is expected to intensify under global warming1, with studies reporting more frequent extreme rain events in many regions of the world2,3,4, and predicting increases in future flood frequency5. Such early, predominantly mid-latitude observations are essential because of shortcomings within climate models in their depiction of convective rainfall6,7. A globally important group of intense storms—mesoscale convective systems (MCSs)8—poses a particular challenge, because they organize dynamically on spatial scales that cannot be resolved by conventional climate models. Here, we use 35 years of satellite observations from the West African Sahel to reveal a persistent increase in the frequency of the most intense MCSs. Sahelian storms are some of the most powerful on the planet9, and rain gauges in this region have recorded a rise in ‘extreme’17 daily rainfall totals. We find that intense MCS frequency is only weakly related to the multidecadal recovery of Sahel annual rainfall, but is highly correlated with global land temperatures. Analysis of trends across Africa reveals that MCS intensification is limited to a narrow band south of the Sahara desert. During this period, wet-season Sahelian temperatures have not risen, ruling out the possibility that rainfall has intensified in response to locally warmer conditions. On the other hand, the meridional temperature gradient spanning the Sahel has increased in recent decades, consistent with anthropogenic forcing driving enhanced Saharan warming10. We argue that Saharan warming intensifies convection within Sahelian MCSs through increased wind shear and changes to the Saharan air layer. The meridional gradient is projected to strengthen throughout the twenty-first century, suggesting that the Sahel will experience particularly marked increases in extreme rain. The remarkably rapid intensification of Sahelian MCSs since the 1980s sheds new light on the response of organized tropical convection to global warming, and challenges conventional projections made by general circulation models.

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Acknowledgements

The research leading to these results received funding from the UK’s National Environment Research Council (NERC)/Department for International Development (DFID) Future Climate For Africa programme, under the AMMA-2050 project (grant numbers NE/M020428/1, NE/M019969/1, NE/M019950/1, NE/M020126/1 and NE/M019934/1). D.J.P. is supported by a Royal Society Wolfson Research Merit Award. We thank K. Knapp, J. Marsham and D. Kniveton for helpful comments; J. Griffin for assistance in preparing the figures; the providers of key data sets used here (Eumetsat; the US National Oceanic and Atmospheric Administration (NOAA); NASA; the European Centre for Mid-Range Weather Forecasts (ECMWF); the meteorological services of Mali, Burkina Faso, Niger and Benin; the World Climate Research Programme’s Working Group on Coupled Modelling); and the centres that provided modelling data.

Author information

Affiliations

  1. Centre for Ecology and Hydrology, Wallingford OX10 8BB, UK

    • Christopher M. Taylor
    • , Danijel Belušić
    • , Phil P. Harris
    •  & Cornelia Klein
  2. National Centre for Earth Observation, Wallingford OX10 8BB, UK

    • Christopher M. Taylor
    •  & Phil P. Harris
  3. Swedish Meteorological and Hydrological Institute, Norrköping SE-601 76, Sweden

    • Danijel Belušić
  4. Centre National de Recherches Météorologique (CNRM), UMR 3589, Centre National de la Recherche Scientifique (CNRS) & Météo-France, 31057 Toulouse Cedex, France

    • Françoise Guichard
  5. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

    • Douglas J. Parker
  6. Univ. Grenoble Alpes, l’Institut de Recherche pour le Développement (IRD), CNRS, Institute of Engineering Univ. Grenoble Alpes (G-INP), Institut des Géosciences de l’Environnement (IGE), F-38000 Grenoble, France

    • Théo Vischel
    •  & Gérémy Panthou
  7. Institut national de l’information géographique et forestière (IGN) Laboratoire de Recherche en Géodésie (LAREG), Université Paris Diderot, Sorbonne Paris Cité, 75205 Paris, France

    • Olivier Bock
  8. UMR7159, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numérique (LOCEAN), Sorbonne Universités, l’Université Pierre et Marie Curie (UPMC)-CNRS-l’Institut de Recherche pour le Développement (IRD)-Muséum National d’Histoire Naturelle (MNHN), 75252 Paris, France

    • Serge Janicot

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Contributions

This study was conceived by C.M.T. and T.V.; C.M.T., D.B., F.G., D.J.P., T.V. and S.J. designed the research; C.M.T., D.B., F.G., P.P.H., C.K. and G.P. analysed the data; and O.B. provided expertise on the GPS analysis. C.M.T. wrote the manuscript, which all authors commented on.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Christopher M. Taylor.

RReviewer Information Nature thanks C. Liu and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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