Sahel - Savanna and Runs from the Atlantic Ocean to the Horn of Africa

Term

The term was first used as a phyto-geographical term, referring to the band of land between 75 and 450 isohyets (bands of precipitation). Subsequent researchers have referred to a wide range of isohyets in determining the location of the Sahel. It has also been used to refer to the countries of West Africa.

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Geography

The Sahel is primarily savanna and runs from the Atlantic Ocean to the Horn of Africa, changing from semi-arid grasslands to thorn savanna. Over the history of Africa the region has been home to some of the most advanced kingdoms benefiting from trade across the desert. Collectively these states are known as the Sahelian kingdoms.

The countries of the Sahel today include Senegal, Mauritania, Mali, Burkina Faso, Niger, Nigeria, Chad, Sudan, Ethiopia, Eritrea, Djibouti, and Somalia.

A map of the region can be viewed here.

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Environment

About 12,500 years ago, the Sahel was a part of the Saharan desert, and was covered in sand dunes which have shaped the landscape that we see today. The Sahel receives 150-500 mm (6-20 in) of rainfall a year, primarily in the monsoon season. The rainfall is characterized by year to year and decadal variability. The two largest determinants of land productivity in the Sahel are water and micro-nutrients, mostly nitrogen and phosphate.

There is a strong correlation between rainfall in the Sahel and intense hurricane activity in the Atlantic.

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Transhumance

Traditionally, most of the people in the Sahel have been semi-nomads, farming and raising cattle in a system of transhumance, which is probably the most sustainable way of utilizing the Sahel. The difference between the dry north with higher levels of soil-nutrients and the wetter south is utilized so that the herds graze on high quality feed in the North during the wet season, and trek several hundred