Predicting Coastal Change in Scotland Across Decadal-Centennial Timescales using a Process-driven One-line Model

Up to 19% of Scotland’s varied and dynamic coast is classified as soft and potentially erodible. These soft coasts are under increasing risk of coastal erosion and coastal flooding, driven by an observed sea level rise (that is predicted to accelerate) and by potential changes in storm wave impact. Understanding future coastal evolution is complex and there is a need for robust models capable of quantifying any predicted coastal change over a range of timescales and scenarios. We present here a method to quantitatively predict coastal evolution and its uncertainty for economically and environmentally vulnerable locations across Scotland. We adapted the Coastal One-line Assimilated Simulation Tool (CoSMoS-COAST) (Vitousek et al., 2017; doi:10.1002/2016JF004065) to simulate the evolution of these sites under climate change scenarios presented by UK Climate Projections 2018 (UKCP18). The model uses a process-based approach to simulate shoreline change via wave-driven alongshore and cross-shore sediment transport processes, as well as long-term shoreline migration driven by relative sea level rise (RSLR). The model is forced using local records of relative sea level change and wave hindcast data, as well as Ensemble Kalman Filtering which assimilates the modelled shoreline to historic positions of Mean High Water Spring over the 20th century. The forecast model is validated with recent shoreline position observations derived from high-resolution topographic surveys, satellite imagery and aerial photography. Shoreline change is then modelled to 2100 under low to high Representative Concentration Pathway (RCP) scenarios within UKCP18, encompassing factors such as anticipated changes in sea level rise and wave action. We report preliminary results of rotational shoreline migration which switches to widespread future shoreline recession under high RSLR scenarios at a test site in east Scotland, where important coastal assets (e.g. transport infrastructure, tourism and cultural heritage) are at direct risk. Developing coastal change predictions for a range of coastal types and future climate contexts can enable more accurate risk assessment and inform resilience and adaptation of Scotland’s most vulnerable coastal areas.