A coupled model framework for simulating barrier island and coastline response to climate change and land use

Abstract:

Exploration of the effects of changing climate and land use on barrier-island evolution requires a model capable of addressing the combined influence of plan-view coastline dynamics, vegetation and dune dynamics, inlet migration and tidal delta evolution, and back-barrier processes. Here, we couple the essential elements of several large-scale models – each critical in understanding coastline response to a subset of the aforementioned processes – into a single geomorphic model of barrier-island evolution. A new quasi-3D spatially-explicit cellular exploratory model, Barrier3D, is used to simulate cross-shore morphodynamics, including shoreface dynamics, dune erosion, and overwash deposition by individual storms. Sea-storm events are generated probabilistically using multivariate vine copulas, a class of copulas particularly well suited to modeling tail dependence in storm variables. Coupling of Barrier3D with the Coastal Dune Model (CDM) allows for modeling of the effects of vegetation and dune evolution following overwash events. Coupling of Barrier3D with the BarrierR Inlet and Environment (BRIE) model accounts for large-scale coastline dynamics including alongshore sediment transport, tidal inlet dynamics, and flood-tidal delta deposition. Using this coupled-model framework, we demonstrate that overwash fluxes are limited when dunes are tall, and are sufficient to maintain island elevation when dunes are short, leading to complex morphodynamic behaviors. We find that for barrier islands with tall dunes that are otherwise prone to passive drowning in Barrier3D, the contribution of tidal inlets to the total transgressive flux (via flood-tidal delta deposition) allows these barriers to withstand higher rates of sea level rise. Hence, the ability of a barrier system to keep pace with sea level is sensitive to dune dynamics, a process typically absent from previous exploratory models of barrier-island evolution. Future work will couple the combined geomorphic model framework with an agent-based socio-economic model to investigate feedbacks between the human and natural components of the coastal system that drive decade-to-century scale evolution of human-occupied coastlines.