Integrating earthquake-induced tsunami scenarios modelling and high-resolution exposure data towards risk assessment in a urban coastal area

Coastal areas in the northeastern Adriatic Sea are exposed to the complex interplay of different geophysical and climate-related hazards, including tsunamis, storm surges, subsidence, and sea-level rise. Although tsunamis are rare and moderate size events in the Adriatic region, still they can have significant impacts in densely populated and highly vulnerable coastal areas. This study presents a comprehensive, scenario-based tsunami risk assessment for the coastal municipality of Lignano Sabbiadoro (Friuli Venezia Giulia, Italy), a major touristic hub characterized by flat morphology, fragile lagoon ecosystems, and marked seasonal variations of population.

The study integrates multi-scenario tsunami modelling, up to date high-resolution exposure data, and buildings vulnerability with the aim to quantify tsunami risk at the urban scale. Tsunami hazard is characterized by means of inundation modelling (water depth) performed by the NAMI DANCE software (e.g. Zaytsev et al., 2019. Sci Tsunami Haz, 38), using a refined topo-bathymetric grid at 25 m resolution. This approach overcomes the limitations of continental-scale probabilistic hazard maps and related simplified empirical relationships by explicitly accounting for local bathymetry, topography, and small-scale coastal features, resulting in highly heterogeneous and realistic inundation patterns.

Exposure for population and residential buildings is assessed at 30 m resolution, following a recently developed methodology (Badreldin et al., IJDRR 2025), to ensure consistency with the tsunami hazard scenarios resolution. The residential building stock is classified into eight typologies based on construction material, age and design code level, and building height. Population exposure is further disaggregated, according to built-up volume and weighted storey distributions, allowing for a more specific characterisation of people potentially affected by tsunami inundation. When dealing with seasonal population variability, the analysis is focused on areas with highest inundation depths (e.g. exceeding 1 m), where population occupancy is empirically estimated in low-season conditions (resident population only) and high-season conditions (full touristic occupancy). This allows us quantifying the number of people potentially affected under different seasonal scenarios and supports discussion on the critical role of tourists in the most severely impacted zones.

Structural damage is quantified using vulnerability curves  for common Italian building typologies available from the literature (e.g. Del Zoppo et al., 2022, Bull Geophys Oceanogr, 63). These curves are combined with consequence models to estimate damage states, economic losses, and potential human impacts. Results indicate that most buildings would experience no or slight non-structural damage, while older, gravity-load-designed masonry mid-rise buildings emerge as the most vulnerable typology and can be potentially damaged in the areas with higher inundation depths.

Overall, the study demonstrates the added value of high-resolution, physics-based, multi-scenario tsunami risk modelling for coastal urban areas. The proposed methodology provides the basis for site-specific emergency planning, land-use management, and the development of integrated multi-hazard risk and adaptation strategies, particularly in touristic coastal regions facing increasing pressures from climate change and urban development.