Introduction. Perspectives on water and land in the Sahel: facing polycrisis

This volume is the result of two different research paces. The first, a slower one, began in the early 1990s by geographers at the University of Padua—Marina and Andrea—and has continued developing research for over 30 years within the Sahelian countries from the Atlantic Ocean to the Red Sea. The research focal points have been the Nile River Valley in Sudan, the Senegal River Valley between Senegal and Mauritania, the Sourou Valley in Burkina Faso, the Office du Niger zone in Mali and, with special intensity, the Lake Chad region between Cameroon, Nigeria, Niger and Chad (Bertoncin & Pase, 2012). Constantly returning to these places, several times and in different years and seasons, has made it possible to observe transformations that are sometimes silent and barely visible but also profound (Jullien, 2009).