An MCDM framework comparable to HEC-RAS modeling for flash flood mapping in a semi-arid region

The downstream part of the Wadi El Ouaar watershed in middle Souss, Morocco, is an important socio-economic and environmental area frequently impacted by severe flooding. Mapping flood-prone areas in this region is essential for protecting the local population and landscape. This study utilizes a Multi-Criteria Decision Making (MCDM) approach, incorporating the Analytic Hierarchy Process (AHP) to integrate six key factors: elevation, rainfall, permeability, slope, distance from the river (DFR), stream power index (SPI), and topographic wetness index (TWI), in order to create the flood susceptibility map. The effectiveness of the AHP model is compared to a hazard map created using the hydrodynamic Hydrologic Engineering Center’s River Analysis System HEC-RAS. This comparison is based on data from 74 historical flood sites collected during extensive field surveys. Although hydrodynamic modeling, such as HEC-RAS, is known for its high accuracy and reliability in small and localized areas. However, it is often time-consuming and resource-intensive. In contrast, our findings demonstrate that the AHP method provides a reliable and efficient alternative for flood susceptibility mapping in larger areas, delivering results nearly as accurate as those of the HEC-RAS model. The AHP map indicates that 42.5% of the study area is at high flood susceptibility, with an accuracy of 89.48%. This approach provides critical data to assist local authorities in prioritizing flood mitigation strategies and highlights the utility of the AHP method in broader applications. The transferability of this methodology can significantly benefit other similar flood-prone regions in Morocco and across North Africa, which are increasingly vulnerable to floods due to climate change and unplanned urban development.