Monitoring Lake Chad Basin Water Quality Using Earth Observation Satellite Observations

The surface waters of the Lake Chad Basin are under threat from climate change and anthropogenic influence. Access to reliable information on the status and evolution of water resources and of their multiple uses is a major challenge for sustainable water resource management. Indeed, water quality monitoring has become one of the most important element of environmental management of the basin's aquatic ecosystems and is essential to provide information and rapid response on its impacts on human health, food production, ecosystem functioning, biodiversity and economic growth. This monitoring has been made possible by the Copernicus program, which has opened up new avenues for satellite applications and services through its free, full and open access basis to high-resolution sensors such as those on-board the two Sentinel-2 (A and B) optical satellites. Thus, the use of remote sensing data from these two satellites allows for addressing and informing communities and stakeholders about water quality changes. A joint effort by CBLT and UNESCO with the support of a French consortium (CNES, INRAE, IRD, OFB, and Magellium as a contractor) has made possible to process a large dataset of Sentinel-2 images over the Lake Chad Basin. The satellite data revealed that the region experiences high variability in water quality as a function of climatic conditions that control the water body's surface area, water turbidity, and productivity. Indeed, a change in turbidity affects the amount of light that can penetrate through the water column, with consequences for photosynthetic processes. Eutrophication in Lake Chad, monitored by the Chlorophyll-a pigment associated with phytoplankton, showed seasonal variability with low eutrophication (Chlorophyll-a content of about 10 ug/L) during the winter and high eutrophication at the end of the dry season (June) with Chlorophyll-a content up to 85 µg/L locally.