Tide-only inundation: a metric to quantify the contribution of tides to coastal inundation under sea-level rise

Sea-level rise is causing coastal inundation events in estuaries, harbours, bays, and tidal rivers to happen more often as predictable daily high and low tides reach higher levels. This can lead to coastal inundation happening under benign weather conditions, as flood thresholds are exceeded due to tides alone without the influence of storm surges or other phenomena. As such, changes in frequency of this 'tide-only' inundation may be a useful metric to quantify the role that sea-level rise plays in modulating the risk of coastal inundation from high still water levels. Here we present a conceptual model for 'tide-only' inundation and propose a practical methodology to formulate tide-only inundation statistics: estimates, historical trends, and future projections. This enables this emerging natural hazard to be fully incorporated into new and existing coastal risk assessment frameworks and considered in coastal management and planning strategies at local and national levels. Further, it leads to a framework that can quantify the role that tides play in coastal flooding as sea levels rise.