Sudan's geography: a clay plain built by the Blue Nile's flood

How the two Niles divide Sudan's water

Every stream and river in Sudan drains into the Nile or towards it, in Britannica's phrasing. The Geography of Sudan article on Wikipedia makes one exception, a small area in the north-east where wadis empty sporadic runoff into the Red Sea and rivers from Eritrea end in shallow evaporating ponds west of the Red Sea Hills. Britannica adds that across much of the country the water never arrives, because the seasonal watercourses are lost in the plains on the way.

The White Nile enters Sudan about 100 kilometres south of Kusti, carrying water from Lake Victoria and the highlands of Uganda, Rwanda and Burundi, and runs north on an extremely low gradient. At Khartoum, around Tuti Island, it meets the Blue Nile, which rises on the Ethiopian Plateau and runs for nearly 800 kilometres through Sudan.

The two rivers keep different seasons. For most of the year the Blue Nile is the smaller, with about a sixth of the combined flow; in August the rain on the Ethiopian highlands swells it until it carries 90% of the Nile's water. Its tributaries the Dinder and the Rahad, which join it between Sennar and Khartoum, flow only in the summer high water.

Below Khartoum the single river runs slowly through the desert in a wide S-shaped course to Lake Nasser behind the Aswan High Dam, past five cataracts that hinder boats at low water.

Sudan has built dams to regulate the flow. The Sennar Dam, 40 metres high, went up on the Blue Nile in 1925 and the Roseires Dam stands about 100 kilometres from the Ethiopian border. South of Khartoum the British built the Jebel Aulia Dam on the White Nile in 1937 to hold its water back until the autumn, when the Blue Nile slackens. About 18,900 square kilometres were irrigated in 2012, by the Geography of Sudan's count.

In November 2023 the Jebel Aulia Dam became a river crossing in the war. With the Shambat Bridge destroyed, the Rapid Support Forces fought a week-long battle for a path over the Nile that could not be destroyed without flooding Khartoum, and took the dam on 20 and 21 November.

What the Blue Nile built between the two rivers

The central clay plains run east from the Nuba Mountains to the Ethiopian border, broken only by the Ingessana Hills, and south from Khartoum. The Geography of Sudan calls them the backbone of the economy, because their water has drawn large numbers of settlements.

At their heart lies the jazirah, Arabic for "peninsula", the land between the Blue Nile and the White Nile. Britannica describes its soil as a deep-cracking uniform clay deposited by the Blue Nile's annual inundations. The Gezira Scheme was developed here to grow cotton for export, and Wikipedia records that it has historically produced more than half of Sudan's revenue and export earnings.

The cracking clays extend from west of Kassala to southern Kordofan, named for the practice of letting them dry and split in the dry months to restore their permeability. They carry the irrigated land of Al Jazirah and Khashm al Qirbah, mechanised rain-fed farming east of the Blue Nile, and the sorghum, sesame and peanuts that traditional cultivators grow west of the White Nile.

The war reached the plain on 15 December 2023, when the Rapid Support Forces moved into Gezira State. After several days of fighting they crossed the Blue Nile at the Hantoob Bridge into Wad Madani, the state capital, and the army retook the city on 11 January 2025. Of the approximately 2,249,163 returnees that the IOM's Displacement Tracking Matrix recorded between November 2024 and August 2025, 43% were in Aj Jazirah and 36% in Khartoum. The IPC expected returnees there to gain little from the 2025 harvest, because they had lost their assets.

When the summer rain reaches each part of Sudan

Sudan lies inside the tropics, and its seasons are set by rain; temperature varies little through the year at any one place. From January to March dry north-easterlies off the Sahara and Arabia hold the whole country, and only a small area in the north-west gets occasional light rain from winds that have crossed the Mediterranean.

Moist south-westerly air reaches the south by early April, Khartoum by July and its usual northern limit around Abu Hamad in August, in some years the Egyptian border. From September the north-easterlies push it back, and by the end of December they cover the country again. Presenting its seasonal forecast at Port Sudan on 3 June 2024, the Sudan Meteorological Authority put the June to September season at more than 80% of the country's annual rainfall, and more than 95% in the centre and north, against a base period of 1991 to 2020.

Britannica's own range runs from almost nothing in the north and centre to 500 to 750 mm a year in the south. The Climate Centre's 2022 climate fact sheet on Sudan adds that the yearly total falls in a few extremely heavy events.

How hot Sudan gets before the rains

Heat peaks at the end of the dry season. In Khartoum May and June are the warmest months, with average highs of 41 °C and readings up to 48 °C, while January lows average 15 °C. In the deserts of the centre and north average highs pass 40 °C for four to nearly six months a year, and the sun shines for more than 4,000 hours in a year. The Climate Centre gives mean annual temperatures of 23 °C to 32 °C across the country, rising by about 0.3 °C a decade between 1961 and 2015.

The haboob, a violent dust storm, comes with the rains. Between May and July, when the moist air first reaches central Sudan, afternoon thunderstorms push ahead of them a yellow or red wall of sand and clay that can cut visibility to zero.

What happens when the rains fail or flood

In some years the south-westerlies reach central Sudan late or not at all, and drought and famine follow; through the 1970s and 1980s they failed often. The Climate Centre dates the most severe recent droughts to 1967 to 1973 and 1980 to 1984, with successive dry years from 1985 to 1993, and cites EM-DAT for more than 27 million people in Sudan affected by drought between 1970 and 2020. The Meteorological Authority ties the dry years to El Niño and a negative Indian Ocean Dipole, and a 2026 World Bank economic brief on Sudan names a possible strong El Niño as a risk to crops and livestock in the central and western regions.

Floods are the other hazard. The Nile and its tributaries rise with rain inside Sudan and upstream in Ethiopia and South Sudan, and flash floods hit low ground that is dry most of the year. In 2020 extreme rainfall set off floods and landslides that affected about 830,000 people.

How the Nile crosses the northern desert

North of Khartoum the river runs between the Nubian Desert to the east and the Libyan Desert to the west, both stony, with drifting dunes and virtually no rain. Britannica describes sand or gravel broken by flat-topped mesas of Nubian sandstone and steep-sided granite hills standing up like islands. The Nubian Desert has no oases. In the Libyan Desert water is limited to a few holes such as Bir an Natrun, where wells serve nomads, caravans and patrols but cannot support an oasis or a settled population.

Between the two, the habitable strip of the Nile valley is alluvium no more than two kilometres wide, and its yield depends on the annual flood. Around Wadi Halfa, the Geography of Sudan records, years and sometimes decades pass without rain.

The semi-desert between the Nile and the Atbara carries a name of its own. UNESCO calls it the Island of Meroe and inscribed its archaeological sites in 2011 as the heartland of the Kingdom of Kush. Two of the three components, Musawwarat es-Sufra and Naqa, lie far from the Nile in an arid zone now devoid of permanent settlement, and the sites' water reservoirs help explain the area's climate and hydrology in the last centuries BCE and the first centuries CE.

Much of Sudan's gold comes from this desert and the hills east of it. Reporting the Sudanese Mineral Resources Company's figures in April 2026, Sudan Tribune put artisanal mining at about 80% of output, concentrated in River Nile, Northern and Red Sea states, and Central Bank of Sudan data counted 14.7 tonnes exported through official channels in 2025.

How Darfur and Kordofan live without perennial streams

West of the White Nile, Darfur and Kordofan have traditionally been treated as one region, and what they share is an absence of perennial streams. People and animals stay within reach of permanent wells, so the population is sparse and unevenly spread across a plateau of Nubian sandstone worn into mesas and buttes.

Western Darfur is an undulating plain dominated by the volcanic massif of Jebel Marra, which towers about 900 metres above it. Britannica makes the Marrah Mountains the watershed between the Nile and the Congo. Their summit, Deriba Caldera, stands at 3,042 metres, the highest point in Sudan. Drainage off the massif supports a settled population and a range of wildlife on the plain below.

Northern and eastern Darfur are semi-desert, with wells that normally go dry in winter. In the jizzu, north-west of Darfur and running on into Chad, sporadic winter rains from the Mediterranean often keep the grazing good into January or February. To the south lies the qoz, sand dunes that the rainy season covers with grass, watered more reliably by bore holes and hafri.

Where the Nuba Mountains rise from the plain

In south-east Kordofan, near the middle of the country, the Nuba Mountains are a cluster of isolated dome-shaped hills rising steeply and abruptly from the plain. Many cover only a few square kilometres, and several larger masses hold internal valleys high above the surrounding ground. The IPC's September 2025 snapshot expected the harvest to bring little relief in the western Nuba Mountains or in North Darfur because of the fighting there.

How the qoz sands grow gum arabic

The qoz is the principal source of gum arabic, tapped from Acacia senegal, known locally as hashab. The tree grows readily on the sands, and cultivators sometimes plant it when they return land to fallow; the belt's other crops are pearl millet, peanuts and sesame, and livestock is its main activity.

The UN human rights office reported in July 2026 that before the war Sudan supplied roughly 70 to 80% of global exports of crude gum arabic. Much of the harvest now comes from conflict-affected areas held by armed actors, and rising exports from neighbouring countries suggested to the office that some of it leaves through illicit channels.

How eastern Sudan climbs to the Red Sea Hills

North-east of the clay plains lies the Butana, undulating land between Khartoum and Kassala with good grazing for cattle, sheep and goats. East of it the flash floods of the Qash River have filled a depression with sand and silt until it stands above the plain as a delta. The land the Qash waters extends 100 kilometres north of Kassala and stays rich grassland, cultivated long after the river has spent itself, and its trees and bushes feed camels from the north.

Beyond the Qash rise the Red Sea Hills, an uplifted escarpment whose seaward face streams have cut into rugged hills. They run north into Egypt and stay cooler than the land around them in the Sudanese summer. Britannica places the Beja here, pastoral nomads who kept their own Bedawi language.

What lies along the Sudanese Red Sea coast

Below the escarpment the coastal plain is dry and barren, rock on the landward side and coral reef on the seaward. The Geography of Sudan gives its width as about 56 kilometres near Tawkar in the south and about 24 near the Egyptian border, against Britannica's 16 to 40 kilometres, and the Sudan article measures the coastline at 853 kilometres. Since the war began the government and its ministries have worked from Port Sudan, the BTI's 2026 report records.

Why UNESCO listed the reefs off Port Sudan

UNESCO inscribed two marine parks as one property in 2016. Sanganeb, 25 kilometres offshore and ringed by water 800 metres deep, is an isolated reef that UNESCO describes as the only atoll-like feature in the Red Sea, with 13 reef zones and more than 300 fish species. Dungonab Bay and Mukkawar Island, 125 kilometres north of Port Sudan, hold coral reefs, mangroves, seagrass beds and a dugong population UNESCO calls globally significant. At inscription the serial site covered 260,700 hectares, and UNESCO noted corals, seagrass and mangroves there at the limits of their global range.

What desertification and war have done to the land

Britannica sorts Sudan's plants into five belts that follow the rain southward, from desert through semi-desert and two kinds of savanna to mountain vegetation. It blames centuries of cultivation, and grass fires that may sweep across more than half the country in a year, for the loss of large areas of natural vegetation, and names overstocking, soil erosion, a falling water table and the advancing desert as further dangers.

The Geography of Sudan puts the desert's advance at 50 to 200 kilometres since rainfall and vegetation records began in the 1930s, most noticeably in North Darfur and North Kordofan, and estimates that Sudan may have lost nearly 12% of its forest cover between 1990 and 2005, about 8.8 million hectares. The Climate Centre's 2022 profile calls desertification the country's greatest environmental problem. The Sudan article, using figures from 2001, counts 21 mammal and nine bird species as endangered and records the Sahara oryx as extinct in the wild.

Six months after the present war began on 15 April 2023, the IOM's Displacement Tracking Matrix had recorded displaced people in 167 of Sudan's 189 localities, across all 18 states, and in August 2026 it monitored 8,583,274 internally displaced people. The Geography of Sudan describes the residents of displacement camps scouring the land around them for water, fuel and food. The BTI's 2026 report says that since the war began environmental rules have been ignored, and that bombardment has destroyed forests, farm projects and water networks.

Which borders Sudan kept after the south left

South Sudan became independent on 9 July 2011, and since then Sudan has had seven land neighbours. Britannica sets them out by direction, with Egypt to the north, Eritrea and Ethiopia to the east beside the Red Sea, South Sudan to the south, the Central African Republic and Chad to the west and Libya to the north-west. The Geography of Sudan gives the land boundaries as 6,819 kilometres in all.

The area after 2011 depends on the source. This catalogue's record carries 1,886,068 square kilometres, the figure in Wikipedia's Sudan article; the Geography of Sudan gives 1,861,484, of which 1,731,671 is land, and Britannica gives 1,840,687.

Two stretches of the frontier are disputed and a third piece of ground is claimed by nobody, and this catalogue records all three without taking a position. The Abyei Area, on the border with South Sudan, received special administrative status under the Comprehensive Peace Agreement of 2005 and is contested by the two states. The Hala'ib Triangle is disputed between Sudan and Egypt and administered by Egypt, and Bir Tawil, on the same border, is claimed by neither.