Africa’s Sahel region is primarily experiencing desertification, which is the process of land degradation in arid and semi-arid areas. This is often caused by a combination of factors, including climate change, unsustainable agricultural practices, overgrazing, and deforestation. As a result, the already fragile environment of the Sahel is becoming increasingly arid, leading to a decrease in size and productivity of this ecosystem.
While a growing population can contribute to environmental pressure, it is desertification that directly relates to the Sahel's decrease in size and viability. In contrast, increasing rainfall is generally not associated with a decrease in the Sahel region.