Mapping the vulnerability of tidal morphologies to Sea Level Rise through an index-based approach

The lagoon landscape is characterized by a diversity of tidal morphologies, such as salt marshes, tidal flats and subtidal platforms, playing an essential role for the ecosystem services these areas provide. The existence of these low-lying morphologies depends on the delicate balance between site-specific bio-geo-morphodynamic processes and relative SLR. Tidal morphologies are at risk of survival since they must keep pace with sea level rise and land subsidence. Given the expected climate change scenario, it is important to identify the most threatened areas, where effective measures are urgently needed. This work presents a novel assessment of the vulnerability of tidal morphologies to relative sea-level rise, using as a study case the Venice Lagoon: the largest wetland in Italy and one of the most important coastal ecosystems of the Adriatic Sea, where the natural hydro-morphological setting is strongly influenced by anthropogenic interventions. Vulnerability is assessed for past, ongoing and future relative SLR conditions through an index-based approach that combines sensitivity and hazard maps generated using a series of indicators such as SLR, land subsidence, morphological setting, and stratigraphic characteristics of Holocene deposits. Results indicate that most of the lagoon area will be at moderate to severe vulnerability in the future, representing a significant worsening of conditions compared to the past. Although the expansion of subtidal areas is anticipated, this will be at the expense of intertidal areas, which will experience a significant and alarming decline. This change contributes to the flattening and deepening of the lagoon's topography, which in turn threatens the diversity of the landscape and is likely to lead to a decline in the ecosystem services provided by these tidal morphologies. The vulnerability maps provide a valuable tool to highlight the areas that need more attention, which can assist policymakers in developing restoration, conservation and mitigation plans. This work is part of the research program RESTORE (REconstruct subsurface heterogeneities and quantify sediment needs TO improve the REsilience of Venice saltmarshes), a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.