The three climate zones of West Africa are Sahelian (rainy season does not exceed three months; irregular rainfall not exceeding 500 mm); Sudanian (precipitations between less than 88 mm in the north of Nigeria and 1 000 mm in the north of Mali); tropical humid (annual mean rainfall approximately 1 500 mm); and equatorial (essentially localized along the Gulf of Guinea, with annual rainfall above 2000 mm).