Abstract:
Extreme climate events, either being linked to dry spells or extreme
precipitation, are of major concern in Africa, a region in which the economy
and population are highly vulnerable to climate hazards. However, recent
trends in climate events are not often documented in this poorly surveyed
continent. Changes in surface temperature gradients and associated changes in
wind shear have been found to be important for MCS intensification in recent
decades. This analysis was extended to Southern West Africa (SWA) by
combining 34 years of cloud-top temperatures with rainfall and reanalysis
data. This study makes use of a large set of daily rain gauge data covering
Southern West Africa (extending from 10° W to 10° E and from 4° N to 12°
N) from 1950 to 2014. The evolution of the number and the intensity of daily
rainfall events, especially the most extremes, were analyzed at the annual and
seasonal scales. The north-south seasonal changes exhibit an increase in mean
annual rainfall over the last decade during the second rainy season
(September-November) linked by both an increase in the frequency of
occurrence of rainy days as well as an increase in the mean intensity and
extreme events over the last decade. Over the south-north gradient of West
Africa, mesoscale convective systems (MCSs) tend to be responsible for the
majority -of annual rainfall. Trends in intense MCS correlate well with intense
rainfall in both rainfall seasons over Southern West Africa. Coldest cloud tops
(intense MCSs) tend to be modulated by positive trends in wind shear during
the first rainy season and by the availability of moisture in the second rainy
season, although both rainy seasons occur mainly under similar conditions.
