Longest river on earth
The Nile meanders through a watershed that is more than 30% arid. The longer of two branches, the White Nile, extends from the mountains east of Lake Tanganyika, through Lake Victoria, to the Nile delta at the Mediterranean Sea. The shorter branch, the Blue Nile, springs from the Ethiopian Highlands, joining the longer branch in central Sudan, and contributes the majority of water entering Egypt.
Most of the population of Egypt and all of its cities, with the exception of those near the coast, lie along those parts of the Nile valley north of Aswan; and nearly all the cultural and historical sites of Ancient Egypt are found along the banks of the river.
People have been farming intensively in the Nile river basin for more than 5,000 years. Today, there are 25 large cities with more than 100,000 people. The Nile delta is home to virtually all of Egypt's 78 million people, where the average population density ranges from 1,000 person/Km2 to much higher in major cities, such as Cairo.
Although the water supply per person is currently ample, the Nile is 1 of 6 river basins in the world with a projected population exceeding 10 million that is predicted to face water scarcity by 2025.
Current threats
Due to heavy human extraction and high evaporation, the Nile river basin and its inhabitants are especially sensitive to climate change. Current water withdrawal for irrigation is so high, that despite its size, in dry periods, the river does not reach the sea.
Climate warming models provide diverging pictures of future river flows in the Nile from a 30% increase to a 78% decrease. In addition, saltwater intrusion into coastal freshwater resources (including aquifers) is likely to increase as a result of sea-level rise due to climate warming and would further reduce the availability of freshwater in the delta region.
The Nile basin traverses the largest number of countries of any basin in Africa; changes in the timing and availability of water under climate change may lead to tension, insecurity and management problems.
