Multi-hazard mitigation measures plan for Ischia Island after the November 26th, 2022, landslide and flood events

The catastrophic landslide and flood events that affected Ischia Island on November 26th, 2022, taking place in the same area previously damaged by an earthquake occurred five years before, underscored the urgent need for integrated multi-hazard risk mitigation strategies in complex volcanic and highly urbanized environments. This study presents a comprehensive Mitigation Measures Plan (MMP) developed under the coordination of the Government Commission for the Emergency and Reconstruction for Ischia Island ( GCER ) to support land planning, accounting for multiple hazards including rainfall-induced debris avalanches, debris flows, rockfalls, floods, and seismic slope instability at the island scale. Moving beyond conventional single-hazard frameworks, the proposed approach integrates geological, geomorphological, hydrological, and geotechnical data with high-resolution topographic information derived from LiDAR and aerial photogrammetry surveys. Physically based numerical models are adopted to reconstruct hazard scenarios and quantify susceptibility patterns. Rockfall trajectories and runout zones, as well as debris-avalanche and debris-flow propagation, are simulated using 3D software. Flood hazard and inundation dynamics are modelled using two-dimensional hydrodynamic simulations under extreme rainfall scenarios, including climate projections based on intensity–duration–frequency analyses. These datasets are further integrated with historical inventories, seismic microzonation studies, and post-earthquake (2017) and landslide (2022) field inspections to ensure a robust multi-source characterization of hazard processes. Results highlight strong spatial coupling between steep volcanic slopes, incised drainage networks, and densely urbanized areas, where exposure is significantly amplified. In response, the MMP was developed, combining structural and nature-based remedial measures such as slope stabilization works, debris retention systems, and underground hydraulic diversion tunnels with non-structural strategies including land-use regulation, monitoring systems, emergency planning, and harvesting schedules for protective forests. The Ischia case study demonstrates the effectiveness of integrated multi-hazard approaches in translating advanced numerical modelling into operational risk reduction strategies, providing a transferable framework for other Mediterranean volcanic islands exposed to interacting natural hazards.