<P> To the south , the Sahara is bounded by the Sahel , a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west . The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha ( a drought - tolerant member of the Chenopodiaceae ) , or northern limit of Cenchrus biflorus , a grass typical of the Sahel . According to climatic criteria , the southern limit of the Sahara corresponds to the 150 mm ( 5.9 in ) isohyet of annual precipitation ( this is a long - term average , since precipitation varies annually ) . </P>
<P> To the south , the Sahara is bounded by the Sahel , a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west . The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha ( a drought - tolerant member of the Chenopodiaceae ) , or northern limit of Cenchrus biflorus , a grass typical of the Sahel . According to climatic criteria , the southern limit of the Sahara corresponds to the 150 mm ( 5.9 in ) isohyet of annual precipitation ( this is a long - term average , since precipitation varies annually ) . </P>
the southern border of the sahara desert is known as the
the southern border of the sahara desert is known as the
the Sahel
the Sahel