The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

Composite rainfall data over the 35-year period 1951-1985 from seven Nigerian synoptic stations, all around latitude I2"N, have been used to examine the 'correlation, or otherwise, between global-scale sea-surface temperature (SST) anomalies and rainfall characteristics on the fringe of the Sahel. Results show that SST anomalies of the Indian, North Atlantic and South Atlantic Oceans are correlated with total rainfall and number of rain days while the anomalies of the tropical East Pacific may have influence on rainfall intensity at the beginning of the rainy season. It is indicated that Pacific El Nifio events may affect the frequency of occurrence of the main rain-producing mechanism in the Sahel; namely, squall lines. Extraordinary warmings in the South Atlantic are also shown to cause considerable shortfalls in expected mean monthly distribution of rainfall, especially in August, the main rainy month in the Sahel.

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