How does rainfall vary from northern to southern parts of the western Sudan?

In the context of western Africa, rainfall patterns are primarily dictated by the north-south oscillation of the intertropical convergence, the boundary where moist, maritime tropical air meets dry, continental air.123

As one moves from northern to southern latitudes, the duration and reliability of the rainy season increase significantly:

• Northern Regions: Areas farther north experience a shorter, more erratic rainy season. At 16° N, the rainy season may last only two to three months, while at 20° N, the region is largely dry throughout the year, with only occasional rains during the high-sun season.2
• Central Regions: As you move south, the drought period becomes shorter and less complete. At 12° N, the dry season lasts approximately half the year.2
• Southern Regions: The rainy season lengthens considerably toward the south. At 8° N, the dry season disappears, and the region may experience up to eight months of rain.2

Generally, precipitation totals increase as the influence of the moist southwest monsoon becomes more dominant and persistent.23