Extreme Sahelian Rainfall Continues to Rise Despite Stable Storm Frequency

Since the 1980s, Sahel rainfall totals, extreme rainfall, and the share of rainfall from extreme events have all trended upward. In observational and reanalysis data sets, these increases are linked to trends in mesoscale convective systems (MCSs) and extreme deep convection (cold clusters). Throughout this period, precipitation metrics have increased first via increases in MCS frequency and the relative increase in cold clusters, and later via an increase in storm precipitation intensity. Until the late 2000s, increases in the frequency of strong storms were supported by increased vertical shear of the zonal wind, as the African easterly jet intensified in response to the strengthening meridional temperature gradient over the Sahel. Afterward, the storm frequency and vertical wind shear stopped increasing. Yet, extreme precipitation continued to increase, as the storms' precipitation intensity increased. We link the higher precipitation intensity to an increase in atmospheric moisture in both the boundary layer and aloft.