Physical Geography

Most of Sudan occupies a great plain rimmed by hills and mountains everywhere but on the north. From elevations of 2,000 to 3,000 feet (610 to 915 m) above sea level along its edges, the plain drops gradually toward the north.

Northern Sudan lies within the Sahara, and includes part of the sandy, almost uninhabited Libyan Desert and all of the Nubian Desert. Separating the desert plains from the coast are the barren Red Sea Hills, whose highest peaks rise to slightly more than 7,400 feet (2,260 m). At about the latitude of Khartoum, Sudan's capital, the desert begins to merge with the grassland that covers much of the central part of the country. Breaking this monotonous expanse of plain are the low Nuba Mountains and other hilly areas. Farther west, near the Chad border, are the Marra Mountains, whose peaks reach 10,000 feet (3,000 m).

Southern Sudan is largely a region of swamps, savannas, and tropical forests. Centered on the southern White Nile valley is the Sudd, an enormous swampy area cut by shifting water channels. Far to the south are hills and mountains. They are dotted with woodlands on their lower slopes, thickly forested at higher elevations. Near the Uganda border rises Kinyeti, at 10,456 feet (3,187 m) the highest peak in Sudan.

The Nile River system is the lifeline of Sudan, extending the length of the country and providing water for people and crops. The main stream of the Nile is formed at Khartoum by the merging of the Blue Nile and the White Nile. Fed by torrential summer rains in Ethiopia's mountains, the Blue Nile rises annually in a great flood that supplies most of the irrigation water used in Sudan. The White Nile, flowing out of Uganda, is considerably longer than the Blue Nile, but loses much of its initial volume through evaporation in the Sudd. Although large tributaries such as the Sobat and the Bahr el Ghazal make up part of the loss, the waters of the White Nile reaching Khartoum make up less than half of the main Nile's annual flow.

Beyond Khartoum, the Nile receives only one tributary, the Atbara, before winding its way across the desert. In the far north, Egypt's Lake Nasser—formed by the Aswan High Dam—extends more than 100 miles (160 km) into Sudan.

Lying entirely within the tropics, and having few areas of high elevation. Sudan has warm to hot weather all year. In the equatorial south, temperatures vary only slightly during the year, with averages of about 80° F. (27° C.) the year round. For seven or eight months of the year, central and northern Sudan have extremely hot weather, with daytime highs often well above 100° F. (38° C.). The rest of the year is somewhat less severe, but hot spells may occur at any time. Great dust storms, known locally as haboobs, often sweep across the drier parts of the country.

Rainfall is low nearly everywhere. Almost no rain falls in the north, but elsewhere a rainy season occurs, increasing in intensity southward. Khartoum, with rain only about two months of the year, receives 6 inches (150 mm) a year. Farther south, the season is longer, bringing 35 inches (890 mm) to Malakal and 50 inches (1,270 mm) to regions near the southern border.