The Role of Sea-level Rise in Coastal Flooding and the Emergence of Tide-only Inundation in Sydney, Australia.

Abstract:

As global mean sea level (GMSL) continues to rise, thresholds corresponding to coastal inundation impacts are exceeded more frequently. Here we relate sea-level rise (SLR) observations and projections to their physical on-the-ground impacts. Using a large Australian coastal city as an example, we show that in Sydney, Australia, frequencies of minor coastal inundation have increased from on average 1.6 to 7.8 days per year between 1914 and present day. In over 80% of cases, the observed coastal inundation events between 1970 and 2015 can be attributed to the predominantly anthropogenic increases in GMSL. Further, we find that impact-producing coastal inundation will occur on average weekly by 2050 under high- and medium- emission/sea-level rise scenarios, and daily by 2100 under high emissions. The proportion of tide-only coastal inundation events (i.e. where no storm surge is required to exceed flood thresholds) will increase with SLR, such that most coastal inundation events, including those considered historically severe, will become a predictable consequence of SLR and astronomical tides. Finally, we discuss the practical merits of distinguishing 'tide-only' events as a metric for monitoring the role that tides play in modulating the coastal inundation hazard. These findings and discussions are important for coastal managers as frequency, severity and predictability of inundation impacts can all now be related to the amount of SLR. By incorporating known historical inundation events, this allows contextualization, visualization, and localization of global SLR and the changing nature of future coastal inundation risk.