Consequently, in addition to the uncertainties associated with the model techniques employed (i.e., model uncertainties), projections of inlet-interrupted coastline changes will also inherit the uncertainties associated with the climate-related drivers (e.g., sea-level rise (SLR), storm conditions, precipitation) and anthropogenic activities considered (i.e., input uncertainties). Another complicating factor is the significant uncertainties associated with the anthropogenic and climate-change impacts that affect the future evolution of inlet-interrupted coasts 26, 27, 28, 29. To adequately resolve the governing physical processes requires a holistic representation of Catchment-Estuary-Coastal (CEC) systems in a model 26. The behavioural dependence of inlet-interrupted coasts on both oceanic and terrestrial processes poses a major complication for long-term modelling of inlet-interrupted coasts. This study was therefore undertaken with the overarching aim of deriving hitherto lacking projections of how this important and globally widespread type of coasts may evolve over the twenty-first century, taking account of both oceanic and terrestrial influences.
Such changes will inevitably lead to severe socio-economic impacts and generate adaptation needs along these heavily populated and utilised coastal zones 11, 19, 23, 24, 25. This means that climate-change impacts (e.g., changes in temperature and precipitation, sea-level rise) and anthropogenic activities (e.g., land-use change, anthropogenic sediment retention, especially by dams) are likely to strongly influence the future behaviour of inlet-interrupted coasts. A majority of these sandy coasts are interrupted by tidal inlets 12, 13, 14, 15, 16, 17, 18-i.e., inlet-interrupted coasts 18, 19, forming an important sub-set of open sandy coasts.īoth oceanic (e.g., change in mean sea-level) and terrestrial (e.g., change in fluvial sediment supply) processes contribute to the long-term (50–100 year) evolution of inlet-interrupted coasts 18, 20, 21, 22. They are complex morphodynamic systems that are commonly expected to erode during the twenty-first century due to rising sea levels and reduced sediment supply 10, 11. Some of the most heavily utilised LECZ areas are fronted by open sandy coasts, which comprise about one-third of the world's coastline 9. LECZ are heavily utilised for a wide range of activities including navigation, tourism, agriculture, marine/ecosystem resources and services, waste disposal, and recreational activities 3, 4, 5, 6, 7, 8. The Low Elevation Coastal Zone (LECZ), defined globally as the areas within 10 m of mean sea-level 1, is home to approximately 600 million people today, a number that is expected to approach one billion by 2050 2. The methods used here need to be applied widely to support evidence-based coastal adaptation. This diverse range of response compared to earlier methods implies that erosion hazards at inlet-interrupted coasts have been inadequately characterised to date. However, the remaining systems are projected to accrete under the same scenario, reflecting fluvial influence.
Under the RCP 8.5 scenario, retreat dominates (90% of cases) over the twenty-first century, with projections exceeding 100 m of retreat in two-thirds of cases. Here, we present novel projections of shoreline change adjacent to 41 tidal inlets around the world, using a probabilistic, reduced complexity, system-based model that considers catchment-estuary-coastal systems in a holistic way. To adequately assess these important changes, both oceanic (e.g., sea-level rise) and terrestrial (e.g., fluvial sediment supply) processes that govern the local sediment budget must be considered. Sandy coastlines adjacent to tidal inlets are highly dynamic and widespread landforms, where large changes are expected due to climatic and anthropogenic influences.