Which of the following has the highest mean annual rainfall?

Freetown, the capital of Sierra Leone, has the highest mean annual rainfall among these cities, receiving approximately 3,600 mm per year. It ranks among the wettest capital cities in Africa.

Freetown's exceptionally high rainfall is explained by its location and relief:

• It sits on the coast of West Africa directly in the path of the moisture-laden south-west monsoon winds blowing from the Atlantic Ocean.
• The Freetown Peninsula mountains (rising to about 900 m) force these moist winds upward, producing intense orographic (relief) rainfall in addition to the convectional rainfall common to the region.

By comparison, Lagos receives about 1,600 mm annually, while Accra and Lome are notably drier (around 800 mm each) because they lie in a rain shadow zone along the Gulf of Guinea coast where the coastline runs parallel to the prevailing winds, reducing moisture uplift.

When comparing rainfall totals for West African cities, remember that orographic factors can greatly amplify rainfall where highland terrain faces onshore winds.