The Mfoundi Watershed at Yaounde in the Humid Tropical Zone of Cameroon: A Case Study of Urban Flood Susceptibility Mapping

Most of the world's major cities currently face the risk of flooding, which is becoming more frequent. Floods often leave behind enormous material damage and, worse still, loss of human life. With this in mind, this paper proposes a conceptual approach to modeling flood risk-sensitive areas in the Mfoundi watershed (95.6 km(2)) that drains Yaounde town, the political capital located in the humid tropical zone of the southern plateau of Cameroon. The multi-criteria decision analysis (MCDA) approach coupled with the analytical hierarchy process (AHP) and the geographical information system (GIS) environment was employed in this study. The method was applied to ten parameters to calculate the flood risk index and hence to generate the flood susceptibility map. The results show five main classes of susceptibility to flooding: very low (9.27 km(2)), low (24.63 km(2)), moderate (22.04 km(2)), high (21.01 km(2)) and very high (19.50 km(2)). Two methods were adopted to validate the flood susceptibility map, which was produced by overlaying 50 regularly flooded points identified in the Mfoundi watershed. The so-called visual method shows that 36 of these points (72%) are found in environments with very high susceptibility and 11 points (22%) are located in areas with high susceptibility, proving that the results reflect reality. The presence of flood points in areas of low and moderate susceptibility could be linked to both human activities and climatic disruption, which sometimes triggers high rainfall. The statistical method (AUC) presents a very good accuracy (0.84 or 84%) of the map produced. This study is important for several reasons: (1) it is carried out in an area with potential for environmental accidents but where very few studies were carried out to delineate these hazards; (2) it provides a basic tool for making decisions about environmental issues for more efficient management of the Mfoundi Watershed; (3) it is also an experimental study representative of the humid tropical forest zone subject to forcings that should be extended to larger scales by covering several climate units in Cameroon.