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What weather patterns create wet and dry seasons in savannas?

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Flat savanna plain with scattered acacia trees under a partly cloudy sky in Serengeti National Park, Tanzania. — Savanna A savanna marked with acacia trees in Serengeti National Park, Tanzania. Africa's Serengeti Plain is commonly used as an example of the savanna biome—a hot, seasonally dry ecological region characterized by an open tree canopy (i.e., scattered trees) above an understory of continuous grasses.

The alternating wet and dry seasons in savannas are primarily driven by the seasonal movement of the intertropical convergence zone (ITCZ).1

The ITCZ is a belt of converging trade winds and rising air that circles the Earth near the Equator. As this zone shifts north and south throughout the year following the Sun, it brings heavy rainfall and thunderstorms to the regions it passes over, creating the wet season. Conversely, when the ITCZ moves away, the area experiences a dry season characterized by significantly reduced precipitation.12

Because savannas are located in tropical regions roughly 8° to 20° from the Equator, their climate is defined by these predictable shifts. The length of the dry season varies by location, typically lasting anywhere from 2 to 11 months, which dictates the specific type of savanna vegetation that develops in a given area.2