Study on the variability of flooded-areas in Lake Fitri in Chad
Etude de la variabilité des superficies inondées dans le lac Fitri au Tchad
Résumé
Located in the heart of Chad, Lake Fitri is the second largest lake in the country just after Lake Chad. With an area of 800 km2 on average, it is one of the most important sahelian wetlands. Its importance as a refuge area both for humans and for wildlife has been clearly demonstrated during the great droughts like that of 1984-1985. Despite the importance of Lake Fitri, its situation is becoming increasingly alarming. The lake and its surroundings are increasingly solicited because of population growth, the expansion of cultivated areas, increasing fishing effort and overgrazing. Complementarities between activities are challenged and disruption of local governance of resources leads to the multiplication of conflicts. In order to think public policies adapted to the lacustrine environment in the Sahel, it is essential to better understand the contemporary landscape dynamics and their relationship to climate variations. Surface waters in the region of Fitri are characterized by a very strong endorheism and an extreme irregularity of resources due to climate variability. To track the spatial and temporal evolution of the lake, we conducted a diachronic analysis of satellite images and climate data. Results based on multispectral Landsat images show the intra-annual variability of the flood for one year (2015), and the inter-annual variability between 1986 (the last episode of total drying up of the lake) and 2016. After a correlation analysis with climate data, we also show that the flow of the Batha River, precipitation and temperature are the three main driving forces of the spatial and temporal variations of flooded areas in the basin of Lake Fitri. If the extension of open water is more important today than in the 1980s, that of flood recession land used for agriculture and animal husbandry is more difficult to assess. Nevertheless, the images clearly show a shifting of exploited sectors outward of Lake, also mentioned by residents of the lake.