Wave-driven storm impacts on Scotland's sedimentary barriers intensify with climate change

Horsburgh, Nicola; Loureiro, Carlos; Rennie, Alistair; Hurst, Martin; Naylor, Larissa A.; Tyler, Andrew

http://hdl.handle.net/10400.1/29533

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Beaches and dunes form vital natural barriers, protecting coastal communities from extreme sea levels. To support coastal management, a geomorphologically-informed understanding of how barriers may be impacted by storm-induced coastal hazards is essential. While storm wave runup can contribute significantly to local extreme sea levels and drive dramatic short- and near-term morphological change to sedimentary coasts, it remains only partly characterised in existing national and regional assessments. This study investigates wave-driven storm impacts at large spatial scales (100–1000 km), at a resolution sufficient to inform local decision making. Using higher resolution national and European datasets, established empirical parameterisations and a simplified barrier morphological evolution model, we predict extreme wave runup and storm impacts on Scotland's wavedominated sedimentary coasts, at 50 m alongshore resolution. We consider a synthetic storm comprised of 25- year return levels of tides and storm surge, and the 1% exceedance of wave height and period, and predict storm impacts for the present-day, mid- and end-century, under RCP4.5 and RCP8.5. Results show that wave runup contributes on average 38% to extreme sea levels, and over 50% in the most exposed locations under present conditions. Nationally, 416 km (65% of the assessed coast) experience barrier erosion during the synthetic storm event, while 72 km (11%) and 27 km (4%) undergo overwash and inundation, respectively. By 2100 the predicted length of inundated coast approximately doubles to 46 km (7%) under RCP4.5, and 59 km (9%) under RCP8.5. Results reveal strong sub-national variability in storm impacts, identifying clear hotspots with the potential for erosion-enhanced flooding.