Wave-tide interaction modulates nearshore wave height

The combined hazard of large waves occurring at an extreme high water could increase the risk of coastal flooding. Wave-tideinteraction processes are known to modulate the wave climate in regions of strong tidal dynamics, yet this process is typicallyomitted in flood risk assessments. Here, we investigate the role of tidal dynamics in the nearshore wave climate (i.e. water depths> 10 m), with the hypothesis that larger waves occur during high water, when the risk of flooding is greater, because tidaldynamics alter the wave climate propagating into the coast. A dynamically coupled wave-tide modelBCOAWST^was applied tothe Irish Sea for a 2-month period (January–February 2014). High water wave heights were simulated to be 20% larger in someregions, compared with an uncoupled approach, with clear implications for coastal hazards. Three model spatial resolutions wereapplied (1/60°, 1/120°, 1/240°), and, although all models displayed similar validation statistics, differences in the simulated tidalmodulation of wave height were found (up to a 10% difference in high water wave height); therefore, sub-kilometre-scale modelresolution is necessary to capture tidal flow variability and wave-tide interactions around the coast. Additionally, the effects ofpredicted mean sea-level rise were investigated (0.44–2.00 m to reflect likely and extreme sea-level rise by the end of the twenty-first century), showing a 5% increase in high water wave height in some areas. Therefore, some regions may experience a futureincrease in the combined hazard of large waves occurring at an extreme high water.