Balancing simplicity with efficiency: a comparison of river flood mapping models on past events on the French Mediterranean coast

Floods are one of the most dangerous and disastrous natural hazards that cause economic damages and human loss. In particular, flash floods related to heavy precipitation represent a major hazard on the French Eastern Mediterranean coast where growing population and tourism increase the exposure and vulnerability of coastal cities to extreme events. A few well recorded severe events have demonstrated the vulnerability of this area to river floods during the last 15 years. Consequently, various modelling approaches has been recently proposed to support flood prevention and mitigation in urban region. However, mapping floods events with limited computational costs remains challenging. In this study, four open-source numerical flood mapping tools are compared regarding their ability at simulating past flood events over five catchments in the southeastern region of France. The flood mapping models range from the simple Height Above Nearest Drainage approach (MHYST) to more complex methods that solve the full shallow water equations (LISFLOOD-FP DG2). Models of intermediate complexity, such as a 1D shallow water solver (HEC-RAS) and a 2D cellular automata (CAflood), are also included. Model evaluations are performed based on water depth accuracy estimation against high water marks data. The flood mapping tools are also compared in terms of flood extent using critical success indices. This study outlines how the more complex models provide the more accurate and realistic flood simulations, however with high computationally demanding which requires the deployment of substantial computer resources before their use in operational flood systems.