Aim
Barrier islands, the everchanging sandy coastal landforms, are sensitive sentinels of climate change. Rising sea-levels and deficient sand supplies could threaten their future resilience and the conservation of the important ecosystem services they provide (e.g., habitats, storm protection). There is consensus among the scientific community that barrier islands will likely move landwards to adapt to sea-level rise, however there is a critical gap in our ability to predict how they will respond to these conditions. Despite the advances in coastal modelling, climate projections of barrier morphodynamic change are still unfeasible, due to either high computational cost (fully process-based models) or to missing physical processes and/or rigorous validation of more simplified approaches (RCMs). MOBILE aspires to improve the current capacity in modelling barrier island adaptation to future marine climate by adopting simplified, yet robust, methodologies that have shown promising results under theoretical and idealised conditions (e.g., the BRIE model; Nienhius & Lorenzo-Trueba (2019)), advancing them by incorporating important, missing, morphological units (dune and marsh; see Fig. 1) and transferring them to decadal to centennial simulations of real-world conditions.
The main aim of MOBILE is to produce a simplified, yet robust, model, suitable for providing meaningful projections for barrier island morphologic adaptation to SLR and changes in storminess, balancing model complexity reduction (necessary to achieve long-term simulations) and comprehensiveness of physical process detail translated into the model (necessary to retain sound physical basis and show good skill). The project will i) implement a modelling scheme able to adequately reproduce barrier island morphological response to a range of drivers (including human- and climate-related) and over distinct timescales (interannual, multidecadal, centennial), thus addressing a critical gap of timescale integration in coastal modelling; and ii) use this model in climate scenarios, to assess the potential future barrier adaptation and to test mitigation strategies.
Methods and datasets
Typically, RCMs are tested on their ability to reproduce specific morphological change (e.g., ability to form spits, reproduce barrier transgression, etc) using either theoretical scenarios, or relatively short-term (e.g. interannual to decadal scales), case-specific data. MOBILE will undertake the major major challenge of real-world testing over the east Ria Formosa barrier chain (Fig. 2), a study area that will allow calibrating against a wide range in barrier morphological response (from fast barrier elongation and longshore growth to barrier drowning and reestablishment) to various forcing factors (natural and human-induced).
Spatiotemporal issues and potential loss of detail by the complexity reduction will be resolved by gradually increasing and overlapping simulation horizons (Fig. 3).
The calibrated RCM will be used to project barrier adaptation to SLR under two climate scenarios (one moderate and one pessimistic) and considering ensemble simulated morphologic change with regards to future storminess, to better represent uncertainties. Model results will be translated to barrier resilience trajectories (evolution of resilience dimensions and system states; Kombiadou et al. (2020)), allowing to identify potential tipping points and the permanence of system shifts for each scenario. The effectiveness of possible mitigation measures (i.e., dune and/or marsh living shorelines, backbarrier nourishment or channel reconfiguration) will be tested through case-specific simulations.
