FAROUK EL-BAZ AWARD for DESERT Research: Late Quaternary Environments in the Nile Basin

The Nile Basin occupies the northeast quadrant of Africa and contains a generous slice of global climatic history. The White Nile rises in the equatorial lake plateau of Uganda and flows across the bed of a former lake to join the Blue Nile at Khartoum. The Blue Nile flows from the volcanic uplands of Ethiopia to emerge onto a mega-fan. The main Nile flows through the eastern Sahara desert northwards into the Mediterranean Sea after a waterless journey of 2 689 km. With a total length of 6 670 km, the Nile is the longest river in the world. The White Nile provides 83% of Nile discharge during the month of lowest flow. The Blue Nile provides 68% of peak flow and 72% of the annual sediment load.

The White Nile, with a flood gradient of only one cm per km, has an unusually well preserved depositional record. During the last 15 ka times of high flow in the Blue Nile and main Nile were synchronous with those in the White Nile. Not all the White Nile flood deposits have been preserved but calibrated radiocarbon dates obtained on fossil freshwater shells and fish bones indicate that high White Nile flood levels at 15-13, 10-9, 8-7.5, 6.5 and 3.2-2.8 ka. Strontium isotopic analysis of these shells shows that the present hydrological regime of the Nile dates back to 15 ka, when overflow resumed from the Ugandan lakes with the abrupt return of the summer monsoon. A severe drought at 4.2 ka caused widespread famine in Egypt. The Meroitic empire flourished during the 3-2 ka wet phase, when cattle-rustling was rife in the Red Sea Hills, and Nero's centurions were foiled in their attempt to find the source of the White Nile by swamps that have since dried out.