Projected sediment supply deficits threaten intertidal wetland resilience to sea-level rise in southeast Australia

Estuarine intertidal wetlands, positioned at the interface of land and sea, are highly vulnerable to sea-level rise and other climate change threats such as flooding and storm-driven erosion. Sustaining these ecosystems and their services requires evidence-based projections of wetland resilience under multiple climate futures while explicitly accounting for uncertainty. Here, we integrated the revised universal soil loss equation with updated rainfall projections from the New South Wales and Australian Regional Climate Modelling (NARCliM2.0) to estimate potential sediment delivery to New South Wales (NSW) estuarine wetlands under both optimistic (SSP1-2.6) and pessimistic (SSP3-7.0) climate change scenarios. We compared modelled catchment sediment yields with both projected rates of sea-level rise and empirically derived vertical accretion rates for mangrove and saltmarsh intertidal wetlands. We found that potential future sediment delivery in NSW coastal catchments is unlikely to assist intertidal wetland accretion to keep pace or exceed sea-level rise. Across near (2020-2039), mid (2050-2069), and far (2080-2099) future epochs, most projections indicated neutral change or modest declines in catchment-derived (allochthonous) sediment supply. Our results provide the first process-based, region-wide assessment of vertical resilience for NSW estuarine wetlands. They highlight the urgent need for adaptation strategies that facilitate landward migration of intertidal wetlands to maintain their representation and services.