The broad, mostly level valleys of the Niger and Benue rivers form Nigeria’s largest physical region. The Niger enters the country from the northwest, the Benue from the northeast; they join at the city of Lokoja in the south central region and continue south, where they empty into the Atlantic at the Niger Delta. Together, they form the shape of a Y. Population densities and agricultural development are generally lower in the Niger and Benue valleys than in other areas.
CLIMATE AND VEGETATION: Nigeria has a tropical climate with sharp regional variances depending on rainfall. Nigerian seasons are governed by the movement of the intertropical discontinuity, a zone where warm, moist air from the Atlantic converges with hot, dry, and often dust-laden air from the Sahara known locally as the harmattan. Temperatures are high throughout the year, averaging from 25° to 28°C (77° to 82°F). In the higher elevations of the Jos Plateau, temperatures average 22°C (72°F). Vegetation also varies dramatically at both the national and local level in relation to climate, soil, elevation, and human impact on the environment. In the low-lying coastal region, mangroves line the brackish lagoons and creeks, while swamp forest grows where the water is fresh. This vegetation has species of tropical hardwoods like mahogany, iroko, and obeche.
RIVERS AND LAKES: About two-thirds of Nigeria lies in the watershed of the Niger River, which empties in to the Atlantic at the Niger Delta, and its major tributaries: the Benue in the northeast, the Kaduna in the west, the Sokoto in the northwest, and the Anambra in the southeast. The Niger is Africa’s third longest river and fifth largest in terms of discharge. Nigeria’s rivers and lakes have not fared well under development. Sensitive wetland habitats, home to many species of birds and other animals, have been cleared for irrigation, and their flood-dependent ecosystems have been damaged by dam construction.
NATURAL RESOURCES: The rural economy that supports most Nigerians is based on the productivity of the land, 33 percent of which is cultivated. Soil fertility varies considerably but is generally poor. Trees, which help prevent erosion, are often used for fuel, lumber, material for tools, fodder for animals, and herbal medicines. As a result, the landscape is becoming increasingly barren of trees, especially in densely populated areas and near larger cities. Petroleum and natural gas, the source of most of Nigeria’s export earnings, are concentrated in large amounts in the Niger Delta.
ENVIRONMENTAL ISSUES: Desertification is a major problem in Nigeria, made worse by massive water impoundment and irrigation schemes. Uncontrolled grazing and livestock migration put tremendous pressure on the environment in some areas. Other environmental threats are settlement within protected areas, brushfires, increasing demand for fuelwood and timber, road expansion, and oil extraction activities. Nigeria has an organized system of nature preserves, game reserves, and national parks in addition to a forest management system.