The flows of Logone and Chari allow to highlight successive hydro-climatic conditions in the Sahelian zone of Cameroon over the study period. In Bongor, the Qmin experienced three successive breaks, in 1971–72, 1998–99 and 2010–11. In N'Djamena, only one break occurred in 1982–83. From 2000, conditions became particularly contrasted. Only 23 % of catastrophic floods registered in the study area occurred during wet years. This shows the important role played by other factors.