MODELED INFLUENCE OF VARIABLE STORM INTENSITY AND SEA-LEVEL RISE ON BARRIER-ISLAND FOREDUNE STABILITY

Coastal foredunes provide barrier islands with a first line of defense against the impacts of hurricanes, extratropical storms, and sea-level rise (SLR). However, the degree of foredune resilience to these intensifying hazards remains largely unquantified. This study uses the process-based AeoLiS model to explore how changes in SLR and storm intensity—and their combined effects—may modify future dune morphology across a range of barrier dune and beach topographies. We simulated cross-sectional dune volume changes for scenarios of SLR (0.3–1.5 m) and/or intensifying storminess (5–50% increase) across modeled dune-beach systems representative of the range of beach slopes and dune-toe elevations found along the northern Outer Banks, North Carolina, USA. Model outcomes suggest that even modest rates of SLR have the potential to exacerbate dune erosion: for simulated SLR of 0.3–0.5 m, dunes experienced net erosion at the toe, with some accretion at the crest. In contrast, SLR of 1.5 m led to complete loss of ~70% of modeled dunes. Interestingly, our results indicate that increased storminess may lead to either net dune erosion (e.g., 0.2–86.0%) or possibly limited net dune accretion (e.g., 0.5–10.2%) at the annual scale. Outcomes demonstrating net dune growth are likely attributable to increased wind speeds; whereas those predicting moderate erosion are likely associated with increased total water levels during more intense storms. When climate forcings were combined, we found that storm-driven accretion has the potential to offset erosion caused by low rates of SLR. The increase in dune erosion during high-risk climate conditions (1.5 m SLR, 5% increase in storminess) was ~2x that for the low-risk climate scenario (0.5 m SLR, 5% increase in storminess), highlighting the threat SLR poses to barrier islands. The precise nature of these future impacts on coupled dune-beach systems is highly dependent on the degree of climate change and the preexisting beach morphology, with systems with lower dune-toe elevations and/or greater beach slopes experiencing the most net erosion. Our exploratory numerical modeling results provide insight into the barrier beach-dune morphologies most vulnerable to dune erosion under evolving climate conditions and can help guide dune construction and management.