The Nile Basin has been a reliable haven for prehistoric human groups for more than a million years. Early, Middle and Late Stone Age artefacts can be seen scattered throughout the Nile Basin, including in areas that are now waterless and inhospitable for all but the hardiest of present-day human communities. Another feature of the Nile Basin is the abundant evidence that the climate has been very much wetter than today on innumerable occasions in the past. All of this prompts us to ask what caused these dramatic changes in climate.

The Nile Basin covers the northeast quadrant of Africa and contains a generous slice of the climatic history of the Earth. It falls under the influence of three major climate systems. In the far north the westerly winds that blow across the eastern Mediterranean in winter bring sporadic rain today to northern Egypt. At intervals in the recent past the influence of these winter rains extended much farther south, bringing precipitation to the Red Sea Hills in the east and, possibly, to the great sandstone plateau of the Gilf Kebir in the west.

In the equatorial south of the Basin the seasonal migrations of the Intertropical Convergence Zone (ITCZ) bring summer rain to the centre of the Basin and to the valleys of the Blue and White Nile Rivers in central Sudan. Here again, there is strong evidence that the influence of the ITCZ once extended much farther north, well into Nubia and the now hyperarid eastern Sahara adjoining the Nile Valley. The most recent northward excursion of the ITCZ was during the Early to Middle Holocene, when groups of Mesolithic people made a living from fishing, hunting and gathering wild plant foods. By about 8,000–7,000 years ago we see the inception of plant and animal domestication in the Nile Valley, several thousand years after its adoption by Neolithic communities in the Fertile Crescent of the Levant and Anatolia. Why was the onset of the Neolithic so late in the Nile Basin compared to farther north?

The African summer monsoon is the third main climate system. The summer floods in the Nile that so intrigued the great Greek traveller and historian Herodotus (484–425 BC) some 2,500 years ago depend on the African summer monsoon in the Ethiopian headwaters of the Nile. During the Early Holocene, the summer monsoon was considerably stronger than today so that the Blue Nile and Atbara Rivers contributed far more water and sediment to the main Nile than they do today. The result was widespread flooding in northern Sudan and Egypt, and the progressive build-up of the Nile flood plain and Nile Delta. These alluvial sediments, when appropriately deciphered, can tell us a great deal not only about both the flood history of the Nile during the last 15,000 and more years, but also about the timing and significance of local contributions to the Nile sediment load from local wadi systems and, later, as the climate became drier, from wind-blown sand and dust.

There is also good evidence that the regional climate has become progressively drier during the last several hundred thousand years. The eastern Sahara was studded with large lakes, including in the region between Bir Sahara and Bir Tarfawi in the presently arid desert west of Aswan at intervals during the Early and Middle Stone Age. The valley of the White Nile was filled with a vast lake during the Last Interglacial. This lake had attained an elevation of 386 m by 110,000 years ago and was more than 500 km long from north to south and up to 80 km wide. A second big lake that refilled the White Nile Valley with the abrupt return of the summer monsoon 14,500 years ago attained an elevation of only 382 m, and although still vast, was much smaller than the Last Interglacial mega-lake. Whether or not these lakes facilitated northward movement through the Nile Valley remains an open question.

The aim of this book is to explore the issues mentioned here in appropriate detail and to seek answers to some of the questions raised. The approach adopted is geographical rather than chronological, allowing the evidence from each of the fifteen or so major physical regions in the Nile Basin to be assessed according to the local geological and geomorphic contexts. Our focus is on the reconstruction of past environmental changes in the Nile Basin, thereby allowing archaeologists to see their work in a more rounded context. We conclude with a review of the uniquely important contributions that marine sediment cores recovered from the submarine Nile Cone have provided to our understanding of Nile flood history and changing patterns of sediment sources and delivery.

Some chapters in this book are quite long and detailed, others less so. By way of defence I can do no better than quote from the introduction to L. C. Beadle (1974), The Inland Waters of Tropical Africa: An Introduction to Tropical Limnology: