The Role of Saltmarsh Restoration in Lowering Shoreline Vulnerability Within an Urban Estuary Environment: A Case Study from North of Portugal

Sea-level rise is accelerating coastal erosion and storm-driven flooding, increasing risks to estuarine ecosystems and coastal communities. Nature-based solutions (NbS), such as those including ecosystem restoration, are widely endorsed for climate change risk mitigation, yet their protective performance under rising sea levels remains poorly quantified across future scenarios. Here we combined scenario-based modelling with spatially explicit exposure mapping to assess how saltmarshes influence shoreline vulnerability under three Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathways (SSP) sea-level rise projections for 2050 and 2100. Using the InVEST Coastal Vulnerability Model and the Lima estuary (NW Portugal) as a case study, we showed that existing saltmarshes currently reduce mean shoreline exposure by approximately 5%, but this contribution declines with sea-level rise, falling to 2.6% by 2100 under SSP5-8.5, resulting in an increase in areas subject to High and Very High exposure risk. But under a saltmarsh revegetation scenario, model results indicated that this revegetation significantly increases the protection across all future scenarios, reducing the number of shoreline points in High and Very High exposure classes by up to 58% and lowering the potential coastal population exposure by up to 27% by 2100 under SSP5-8.5. However, the protective effect of saltmarshes diminished under the most extreme sea-level rise trajectories, indicating that saltmarsh revegetation alone may not be enough to fully offset accelerating coastal hazards. Our results demonstrate that saltmarsh restoration can deliver meaningful climate adaptation benefits; however, to safeguard estuarine systems and coastal communities under accelerating climate change in the long term, restoration actions must be integrated into broader adaptation strategies.