Variability and Predictability of Sub-Seasonal to Seasonal Rainfall over Africa

While North Africa receives most of the annual rainfall during the summer (June – September; JJAS), equatorial Africa within 10oN/S, receives annual rainfall two-three times a year; during March-May, September-November, and/or December-February. It is well documented that rainfall features high variability both in time and in space. Past studies noted that Sahelian Africa is recovering from droughts of the 1980s and 1990s well into the 2000s. Although preliminary analysis shows an increase in Sahelian rainfall, there is no consensus on “recovery”. Also, the nature of this “observed” change in rainfall is not well documented. Some studies relate the rainfall increase to an increasing Sahelian storms and frequent convective systems associated with north-south temperature gradients and increasing wind shear. But the details of the variability of intense convective systems is lacking. It is not established that increasing frequency of intense rain-bearing systems are contributing to the decade long positive trend in rainfall. We revisit the spatio-temporal variability of rainfall and investigate the extended dry and wet periods during the rain seasons and their contribution to the annual rainfall. The interaction between local and remote mechanisms that determine these variabilities will also be explored. We will attempt to shed light as to whether there has been an increase in “few instances of heavy rainfall or increasing wet periods that make up or exceed the total expected rainfall but are less evenly distributed in time”, as suggested in past studies.