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How can longer droughts change savannas into grasslands or deserts?

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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.

Longer and more intense droughts, driven by anthropogenic climate change, can fundamentally alter the structure of savannas. These shifts occur through several ecological mechanisms:

Direct Vegetation Loss: Sustained droughts can lead to the direct die-off of trees, which are essential components of the savanna landscape. As woody plant cover declines, the ecosystem may transition toward a grassland state.1
Altered Fire Dynamics: Droughts impact the frequency and severity of wildfires. Because savannas rely on a balance between grass and woody plants, changes in fire patterns can destroy saplings or alter plant community dynamics, further pushing the environment away from its historical state.12
Desertification: In densely settled regions, the combination of drought and human-induced pressures—such as overgrazing by livestock and the overuse of woody plants for fuel—accelerates soil erosion. This degradation can lead to desertification, effectively transforming the savanna into a desert.1

Because savannas act as transition zones between rainforests and deserts, they are highly dynamic; these environmental stressors can shift the balance of vegetation along this continuum.2