Optimality of flood influencing factors for flood hazard mapping: An evaluation of two multi-criteria decision-making methods

Abstract

• Two Multi-criteria Decision-Making (MCDM) methods were evaluated by applying two groups of flood influencing factors. • Compared the suitability of the two MCDM methods in the identification of flood hazard areas. • Evaluated the influence of each group of flood influencing factors on the flood hazard maps. • Validated the resulting flood hazard maps with historical flood record to ascertain the accuracy of the two MCDM methods. Flooding is a serious and recurring natural hazard. Flood hazard mapping requires synthesizing relevant factors that affect flood occurrence to allow for an accurate geographical assessment of flood characteristics for flood management activities. Two Multi-criteria Decision-Making Methods consisting of the Analytical Hierarchy Process (AHP) and Fuzzy-AHP (F-AHP) methods were applied in identifying flood hazard areas by using two groups of flood influencing factors (FIFs) to decrease the number of pairwise comparisons required for AHP to enable the use of an optimum set of factors. For the AHP and F-AHP methods, fewer pairwise comparisons can reduce uncertainty caused by inconsistency in the decision-making process of a larger number of factors. Thirteen non-correlating FIFs were selected and divided into two groups namely the flood susceptibility factors group (FSFG) and flood vulnerability factors group (FVFG). FSFG consisted of drainage density, elevation, land use, slope, rainfall, infiltration, topographic wetness index, time of concentration, and flood depth) and FVFG consisted of distance from inundated locations, distance from rivers, population, and distance from roads & buildings. The methodology was evaluated using three test scenarios; a) FSFG group only; b) FVFG group only; c) flood susceptibility and vulnerability factors group (FSVFG). The AHP and the F-AHP methods were applied in evaluating the influence of each group of factors on the flood hazard maps. The result of the evaluation indicated that the FVFG had the highest influence based on the spatial extent of the region by each varying flood hazard class (low to very high) on the generated flood hazard maps. The FVFG had (40.15% and 42.09%) influence in comparison with FSFG (25.85% and 25.26%), and FSVFG (34% and 32.65%) for the AHP and F-AHP methods respectively. The findings from the sensitivity analysis showed similar findings with the AHP and F-AHP methods confirming the accuracy of the methods. The validation of the AHP and F-AHP methods showed excellent compatibility with the historical flood record and affirmed the relevance of applying FSVFG. The methodology applied in this study can be a dependable support tool in flood risk analysis and management for efficient decision-making to achieve a resilient city.