Relief

The country’s major topographical features include a large river basin, a major valley, highplateaus, three mountain ranges, and a low coastal plain. Most of the country is composed of the centralCongo basin, a vast rolling plain with an average elevation of about 1,700 feet (520 meters) abovesea level. The lowest point of 1,109 feet (338 meters) occurs at LakeMai-Ndombe (formerly Lake Leopold II), and the highest point of 2,296 feet (700 meters) is reached in the hills of Mobayi-Mbongo and Zongo in the north. The basin may once have been an inland sea whose only vestiges are LakesTumba and Mai-Ndombe in the west-central region.

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The north-southWestern Rift Valley, the western arm of theEast African Rift System, forms the country’s eastern border and includes LakesAlbert,Edward,Kivu,Tanganyika, andMweru. This part of the country is the highest and most rugged, with striking chains of mountains. TheMitumba Mountains stretch along the WesternRift Valley, rising to an elevation of 9,800 feet (2,990 meters). The snow-covered peaks of theRuwenzori Range between Lakes Albert and Edward lie astride the Ugandan border and mark the country’s highest elevation of 16,763 feet (5,109 meters) atMargherita Peak. The volcanicVirunga Mountains stretch across the Western Rift Valley north ofLake Kivu.

High plateaus border almost every other side of the central basin. In the north theUbangi-Uele plateaus form the divide between the Nile and Congo river basins. Rising to between 3,000 and 4,000 feet (915 and 1,220 meters), these plateaus also separate the central basin from the vast plains of theLake Chad system. In the south the plateaus begin at the lower terraces of the Lulua and Lunda river valleys and rise gradually toward the east. In the southeast the ridges of the plateaus ofKatanga (Shaba) province tower over the region; they include Kundelungu at 5,250 feet (1,600 meters), Mitumba at 4,920 feet (1,500 meters), and Hakansson at 3,610 feet (1,100 meters). The Katanga plateaus reach as far north as theLukuga River and contain the Manika Plateau, the Kibara and the Bia mountains, and the high plains of Marungu.

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The northern escarpment of the AngolaPlateau rises in the southwest, while in the far west a coastalplateau zone includes the hill country of Mayumbe and theCristal Mountains. A narrow coastal plain lies between the Cristal Mountains and the Atlantic Ocean.

Drainage and soils

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The Congo River, including its 1,336,000-square-mile (3,460,000-square-km) basin, is the country’s main drainage system. The river rises in the high Katanga plateaus and flows north and then south in a great arc, crossing theEquator twice. The lower river flows southwestward to empty into the Atlantic Ocean belowMatadi. Along its course, the Congo passes through alluvial lands and swamps and is fed by the waters of many lakes and tributaries. The most important lakes are Mai-Ndombe and Tumba; the major tributaries are theLomami, Aruwimi, andUbangi rivers and those of the greatKasai River system. In addition, the Lukuga River links the basin to the Western Rift Valley.

Soils are of two types: those of the equatorial areas and those of the driersavanna (grassland) regions. Equatorial soils occur in the warm, humid lowlands of the central basin, which receive abundant precipitation throughout the year and are covered mainly with thick forests. This soil is almost fixed in place because of the lack of erosion in the forests. In swampy areas the very thick soil is constantly nourished by humus, the organic material resulting from the decomposition of plant or animal matter. Savanna soils are threatened by erosion, but the river valleys contain rich and fertile alluvial soils. The highlands of theGreat Lakes region in eastern Congo are partly covered with rich soilderived from volcanic lava. This is the country’s most productive agricultural area.

Climate

Most of Congo lies within the inner humid tropical, or equatorial, climatic region extending five degrees north and south of the Equator. Southern Congo and the far north have somewhat drier subequatorial climates.

The seasonally mobileintertropical convergence zone (ITCZ) is a major determinant of the climate. Along this zone the trade winds originating in the Northern and Southern hemispheres meet, forcing unstable tropical air aloft. The air that is forced upward is cooled, and the resulting condensation produces prolonged and heavy precipitation. In July and August this zone of maximum precipitation occurs in the north; it then shifts into central Congo in September and October. Between November and February the southern parts of the country receive maximum precipitation. Thereafter the ITCZ moves northward again, crossing central Congo in March and April, so this zone has two rainfall maxima. The extreme eastern highlands lie outside the path of the ITCZ and are subject to the influence of the southeastern trade winds alone. In addition to the ITCZ, elevation andproximity to the Atlantic Ocean and its maritime influences also act as factors of climatic differentiation.

The country is divided into four major climatic regions. In the equatorial climate zone, temperatures are hot, the average monthly temperature rarely dropping below the mid-70s F (low to mid-20s C). Humidity is high, and it rains throughout the year. Annual precipitation at Eala, for example, averages 71 inches (1,800 mm). The tropical or subequatorial climate zone, marked by distinct dry and rainy seasons, is found north and south of the equatorial region. The dry season lasts from four to seven months (usually April to October), depending largely on distance from the Equator. InKananga about 63 inches (1,600 mm) of precipitation falls annually. Short dry spells of several weeks’duration may occur during the rainy season.

The Atlantic climate zone is confined to the west coast. The low elevation and the coldBenguela Current are the major influences. AtBanana the average annual temperature is in the high 70s F (mid-20s C), and precipitation averages about 30 inches (760 mm) yearly. Themountain climate occurs in the eastern high plateaus and mountains. InBukavu, for example, the average annual temperature is in the mid-60s F (high 10s C), and annual precipitation levels measure about 52 inches (1,320 mm).