Modelling the Geomorphological Evolution of Coastal Wetlands Under Rising Sea Levels: A Reduced Dimensional and Multi-Temporal Evaluation

Abstract

Models that project or simulate the response of coastal wetlands to sea-level rise are tools used by decision makers. Appropriate spatial and temporal scales for calibration and evaluation are important decisions at the model development and implementation stages, particularly when simulating real-world conditions. Given the uncertainty in factors influencing geomorphological evolution and data used to parameterise models, reduced complexity models that seek to parameterise the primary processes influencing substrates may be as effective at supporting decisions as more complex models. Here we tested the efficacy of zero-dimensional models of varying complexity to project changing tidal position of coastal wetlands under future sea-level rise scenarios. The simpler approach projected vertical elevation gain based on a single variable, while the complex approach was structured similar to recent landscape scale models that explicitly incorporate processes contributing to mineral and organic matter addition, and autocompaction. While a deterministic approach was used, appropriate effort was directed towards validation, unlike many similar studies. Model comparison and evaluation was undertaken against observed wetland changes occurring at three temporal scales: years, decades and millennia. Model evaluation at the decadal scale, consistent with projections needed to guide decision making, showed that model outputs aligned with observations, irrespective of the application of simple or complex modelling. We found coastal wetlands can adapt in situ provided sediment supply is sufficient, but this capacity is increasingly limited as rates of relative sea-level rise accelerate. This will necessitate decisions to promote landward retreat or defend coastal assets from inundation.

Keywords: Mangrove and saltmarsh, zero-dimensional modelling, reduced complexity modelling, sea-level rise impacts