What causes the seasonal rainy and dry periods in Africa’s savanna climate regions?

The seasonal rainy and dry periods in Africa’s savanna, or tropical wet-and-dry, climatic regions are primarily driven by the seasonal migration of the intertropical convergence zone (ITCZ).12

The ITCZ is the area where northern and southern air masses converge and air is forced aloft, resulting in intense precipitation. The movement of this zone follows the seasonal path of the Sun.1

• Rainy Season: During the period of high sun, the ITCZ moves into a region, bringing maritime air masses that produce rainfall. The duration of this rainy season depends on the region's proximity to the Equator, with areas closer to the Equator experiencing longer periods of rain.12
• Dry Season: During the period of low sun, the ITCZ shifts away, leaving the region under the influence of dry continental tropical air masses. In some areas, such as western Africa, this dry period is also associated with the harmattan, a warm, dry, and dusty northeasterly wind blowing from the Sahara.123

While these broad patterns define the savanna climate, local variations can occur due to factors like altitude, proximity to the sea, and the influence of cool ocean currents.12