Landward Migration of Coastal Wetlands under Land-Use Constraints in Australia

Sea level rise (SLR) is a key driver in altering spatial boundaries, species distribution, and functioning of coastal wetlands in the 21st century. Wetland adaptation to SLR depends on vertical accretion and landward migration; however, the magnitude and rate of these processes remain uncertain and are constrained by factors such as sediment supply and the availability of inland accommodation space. To enhance adaptive capacity, spatially explicit assessments are critical for identifying areas suitable for wetland migration. Nevertheless, much of the existing literature emphasises global-scale analyses with coarse spatial resolution and limited use of local SLR projections, which reduces their applicability for regional and local decision-making.

We conducted a scenario-based assessment of the potential extent of landward migration for mangroves and saltmarshes in Victoria, Australia, using high-resolution (10 m) regional spatial data under two socio-economic pathways (SSP2 and SSP5) for 2070 and 2090. The results indicate that, for both ecosystems, potential area gains from landward migration exceed losses from seaward inundation. For saltmarshes, ecosystem losses are driven more by mangrove encroachment (53%) than by inundation (47%). Land tenure emerges as a key factor shaping wetland migration capacity. Future accommodation space for mangroves is largely under public ownership (56%), primarily within protected areas and nature reserves (56.2%), providing a relatively secure buffer for inland migration. In contrast, most accommodation space for saltmarshes is privately owned (56.4%) and predominantly associated with primary production land use (45.4%). Without specific management actions, saltmarshes are likely to experience losses from both expanding mangroves and ongoing land-use pressures. Overall, these findings provide valuable insights to support stakeholders in scenario-based planning and the management of coastal and urban areas to enable wetland adaptation to rising sea levels.