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.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
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.
Extended data figures
About this article