1Lake Chad is a water expanse with no access to the sea, subject to evaporation, which however is not saline. In the 1950s, this peculiarity prompted hydrologists, soil scientists and biologists to undertake research on the lake which, at the time, extended over 20,000 square kilometres. They analysed the system’s hydrological mechanics and showed that, at depth, salt seeps into the aquifer, forming saline water tables which underpin the fresh water layer. This research stopped abruptly in the 1970s because of the war, and only resumed in the late 1990s. By that time, the lake had shrunk considerably. A satellite image taken in 2001 estimates its surface area at 3,000 square kilometres. Nevertheless, scientists were unsure how to interpret this variation in terms of functioning or future evolution. A number of studies were undertaken. Remote detection and field work made it possible to determine past variations of Lake Chad, showing that 8,000 years ago, during a particularly hot climatic period, the lake’s surface area was 350,000 square kilometres. Therefore, the fluctuations of Lake Chad are not new.

Drying up of Lake Chad.

2Meanwhile, hydrologists made the most of new technologies to clarify current water stratification in the aquifer. Water on the surface is fresh yet rich in bacteria and non-potable, whereas deeper water layers are salty but potable. Improving knowledge of water body structures can help optimise the quality of freshwater boreholes.

Hydrology measurement, Lake Chad.

3In 2010 however, field research was halted once again due to security issues, before resuming by recovering data accumulated since the 1990s, which forms a baseline for supporting Lake Chad’s development and planning programmes. It is notably used to document the various water transfer scenarios from the Congo basin to the Lake Chad basin, which are largely based on data collected by Orstom and IRD over several decades.