What landform in Africa might have influenced the Bantu people to migrate south instead of north?

The landform that may have influenced the Bantu people to migrate south is the Sahara Desert. The Sahara receives very little rainfall each year. In fact, less that 10 inches per year is normal. This makes water sources very scarce in the area. Also, because of the lack of water and rich soil, vegetation is sparse. These factors would have made it an easy decision for the Bantu's to head Southward.