Flood Risk Modelling Using the HFPA (Hierarchical Fuzzy Process Analysis) Method: Example of the City of Thies, Senegal

Abstract

Based on the perception of flood risk factors derived from the lessons learned by the main stakeholders, namely the members of the National Emergency Response Plan (ORSEC) and the people affected by floods in the study area (Thies, Senegal), this work consists of modelling the flood risk using Hierarchical Process Analysis (HPA). This modelling made it possible to determine the coherence index (CI) and the coherence ratio, which were evaluated respectively at 0.27% and 5% according to the perception of the members of the ORSEC Plan, and at 0.28% and 5% according to the perception of the disaster victims. These results show that the working approach is coherent and acceptable. We then carried out Hierarchical Fuzzy Process Analysis (HFPA), an extension of HFPA, which seeks to minimize the margins of error. FPHA uses fuzzification of perception contributions, interference rules and defuzzification to determine the Net Flood Risk Index (NFRI). Integrated with ArcGIS software, the NFRI is used to generate flood risk maps that reveal a high risk of vulnerability of the main outlets occupied by human settlements.