Flipping Book | Africa's Giants | Salini Impregilo Library

of climatic changes, such as desertification, flooding and glaciation. That humans can adapt, and that we possess the mechanisms to face up to these large-scale changes, is the result of an anthropic journey which has borne witness to transformations affecting the entire planet, bringing new forms to continents and oceans. Tracing landscape transformations necessitates, therefore, an understanding of geographical changes, as well as of resources and the limits for human survival. Geography works on its own timescale, one which precedes human history and bears influence on it in many different ways. The great periods of migration, which began after the desertification of the Sahara, around the fourth millennium B.C.E., gave rise to stable, populated areas along the two main geographical axes: the Rift Valley and the southern border of the Sahara desert. Climate instability, biological diversity and physical changes fostered the first forms of steady settlement between the Rift Valley, the Great Lakes Region and the Nile; by exploiting this great natural corridor, which dissects Africa from south to north, man was able to begin his exploration of the planet, gradually approaching the Mediterranean and the Middle East. The southern border of the Sahara desert, which stretches for more than 6,000 kilometres from the Atlantic Ocean to the Red Sea, has for thousands of years been a “dynamic frontier”. Man’s ability to exploit the few resources available here has transformed the landscape, allowing the formation of an extraordinarily densely populated area. From the 12 th to the 10 th century B.C.E., some of the most important African civilisations developed along the Rift Valley and the southern border of the Sahara desert. The history of Africa unfolded along these two continental axes which, according to Basil Davidson, provided the ideal geographical and climatic conditions for an “ecological society”, maintaining a balance between available resources. Such an “ecological society” can perhaps be seen as a prelude to a future landscape, able to resist the present demographic and climatic challenges. The importance of the Rift Valley and of the southern border of the Sahara desert is still evident today. The Africa Water Atlas , published in 2010 by the United Nations Environmental Programme, brings to the fore the opportunities presented by a sustainable and responsible use of the continent’s water resources. Within this framework, the Rift Valley and the southern border of the Sahara desert play a fundamental role: they are largely characterised by semi-arid climates and a widespread, dense population (over 20 inhabitants per km 2 ). In Senegal, Burkina Faso, Mali, Niger, Nigeria, Chad, Sudan, Ethiopia, Somalia, Kenya, Malawi, Tanzania, Zambia, Zimbabwe, Mozambique and South Africa more than one hundred million people still live in rural environments where the annual rainfall is, for the most part, insufficient and food insecurity is becoming ever more palpable. While confirming the major role played by these areas in the continent’s ecological balance, the data highlights a series of basic questions concerning the regulation of a sustainable water balance. If we compare data on land use, vegetation, rainfall, evapotranspiration and population in Sahelian inland areas, we notice that large water-deficit areas sit side-by-side with surplus regions. In water surplus areas the annual rainfall is quite remarkable: the quantity of water not subject to infiltration and evapotranspiration generates a consistent runoff, which represents an important resource. Along the sub- Saharan border, between Senegal and Ethiopia, the annual water runoff is equal to a stock of 20 to 30 thousand cubic metres for each square kilometre. A smaller, though no less remarkable, quantity of run-off is observed along the north-south axis, between Tanzania and South Africa. This data provides the basis for a large-scale hydro-political strategy, uniting small interventions (vital for local economies) and large transnational projects.