Physical context

Geology

Central Africa is formed mainly of an enormous bloc of Precambrian rocks that crop out in an arc around a central sedimentary basin, separating it from the sedimentary Chad Basin to the north and the coastal sedimentary basin to the west.

Geological formations of Central Africa
Soil Atlas of Africa

The Soil Atlas of Africa was published on 29 April 2013. The Atlas explains the origin and functions of the soils, describes the different types of soil and the usefulness for addressing local and global problems. It describes the main threats to the soils and the measure taken to protect Africa's soil resources.

The Soil Atlas of Africa is the result of collaboration between the European Union, the African Union, and the United Nations FAO, to support and encourage sustainable use of soil resources in Africa, and the Global Soil Partnership for Food Security.

To find the Atlas and download the data:
http://esdac.jrc.ec.europa.eu/content/soil-map-soil-atlas-africa

Hydrography

Central Africa is part of five major river basins or groups of river basins.

River Length (km) Basin area(km2) Flow rate (m3/sec)
1 Congo 4374 3600000 41000
2 Nile 6670 3349000 5100
3 Chad (Chari) 949
4 Niger (Bénoué) 1400 870
The coastal rivers of the Gulf of Guinea
5 Cross 75000 569
6 Wouri 11700 308
7 Sanaga 1043 133000 2060
8 Nyong 27800 443
9 Ntem 31000 348
10 Wele
11 Muni
12 Komo
13 Ogooué 1200 205000 4400
14 Nyanga 25000 450
15 Kouilou-Niari 60000 700

Source: WRI-OFAC

The Congo River Basin, where annual renewable water resources amount to about 1.3 billion m3 is the biggest of these basins and the biggest in Africa. It accounts for close to 30% of Africa's water resources and covers 4 million km2. The Congo River has an average annual flow rate of 41,000 m3/sec (Nkounkou and Probst, 2017). The basin covers parts of ten countries but 85.3% of the Congo River Basin is located in largely forested areas of four countries : Cameroon, Central African Republic, Democratic Republic of Congo and Republic of Congo. The Congo basin's stream network is very dense and consists of a complex network of rivers, vast freshwater swamp forests, and lakes.

GIS Data     Geoportal

For more information on the stream network, particularly its relationship to the forest and to ecosystem goods and services, see Chapter 9 of the State of the Forests 2008.

Rainfall

Annual average rainfall in Central Africa is highest in the area closest to the Gulf of Guinea: 3000 mm in Libreville, 3200 mm in Bata, 3400 in Douala, 6000 mm in the southern part of Bioko Island and close to 12,000 mm in Debunscha in the southwestern foothills of Mount Cameroon. Towards the south, precipitation declines rapidly: at the mouth of the Congo River, it is less than 1000 mm.

Further from the coast, the Congo basin's rainforests receive between 1700 and 2000 mm of rain. The areas with the highest rainfall are located close to the equator on the Chaillu mountains and on the centre and eastern edge of the central basin. Further from the equator, rainfall drops to under 1000 mm in the north of Cameroon near Lake Chad, the northeast of the Central African Republic and in certain parts of southeast DRC. The Albertine Rift valley also has some very arid areas near lakes Albert and Edward and in Tanganyika.

Topography

The forests of Central Africa mainly cover the vast alluvial plain of the Congo, lying at an altitude of between 300 and 600 m and surrounded by generally tabular plateaux with altitudes between 600 and 1000 m. To the north and south, these plateaux (which separate the Congo basin from the Chad and Zambesi basins) cover areas that are almost completely outside the rainforest zone.

To the east, forests cover the plateaux that form the foothills of the mountain range along the Albertine rift. This range is close to 1000 km long from north to south, peaking at 5100 m in the Ruwenzori range and 4500 m in the Virunga Mountains.

To the west, the Congolese plain is separated from the alluvial coastal plain which extends over 150 km where it reaches Gabon, by a series of plateaux and mountain ranges barely over 1000 m high that separate the waters of the Congo from those of the numerous coastal rivers.

GIS Data     Geoportal

In Cameroon, these plateaux spread over a large part of the country, punctuated to the northwest and the north by high volcanoes forming an arc from Bioko Island and Mount Cameroon to the Bamenda and Adamawa plateaux and even the Yade plateau in Central African Republic.

About 65% of Central Africa's tropical rainforests are located at altitudes of 300-600 m, 30% at altitudes between 600 and 1650 m and 5% between 0 and 300 m. Only 1% of these forests are composed of montane forests at altitudes over 1650 m.