The sub-Sahelian sector represents the transition zone , receives an average annual rainfall of 400 -- 600 millimetres ( 16 -- 24 in ) .
The sub-Sahelian sector represents the transition between the Sahelian and Sudanian bioclimatic zones .
The sub-Sahelian sector represents the transition zone , receives an average annual rainfall of 400 -- 600 millimetres ( 16 -- 24 in ) and represents the transition between the Sahelian and Sudanian bioclimatic zones .