Namibia (formerly South West Africa) is situated in the south west of the continent of Africa, bordered by the Atlantic Ocean on the west, Angola and Zambia to the north, Botswana to the east and the Republic of South Africa to the south . With a mean annual rainfall of approximately 270 mm, Namibia is rated to have the driest climate in sub-Saharan Africa. The only perennial rivers flow along parts of the northern and southern borders, and the country is almost entirely dependent upon ephemeral rivers and groundwater.