Single extreme storm sequence can offset decades of shoreline retreat projected to result from sea-level rise

Episodic coastal sediment deposition during extreme storms can offset shoreline retreat projected in response to sea levels rise by decades, according to high-resolution morphology data from Australia, the UK and Mexico, collected after extreme storm events. Extreme storms cause extensive beach-dune erosion and are typically considered to enhance coastal erosion due to sea-level rise. However, extreme storms can also have a positive contribution to the nearshore sediment budget by exchanging sediment between the lower and upper shoreface and/or between adjacent headlands, potentially mitigating some adverse sea-level rise impacts. Here we use three high-resolution morphological datasets of extreme storm-recovery sequences from Australia, the UK and Mexico to quantify the nearshore sediment budget and relate these episodic volume changes to long-term coastal projections. We show that sediment gains over the upper shoreface were large (59-140 m(3)/m) and sufficient to theoretically offset decades of projected shoreline retreat due to sea-level rise, even for a high-end greenhouse gas emissions scenario (SSP5-8.5). We conclude that increased confidence in shoreline projections relies fundamentally on a robust quantitative understanding of the sediment budget, including any major short-term sediment contribution by extreme storms.

Automated summary

High-resolution morphology data from Australia, the UK and Mexico shows that episodic coastal sediment deposition during extreme storms can offset projected shoreline retreat caused by sea level rise. Extreme storms, although causing erosion, can also contribute positively to the sediment budget by exchanging sediment between different areas, mitigating the impacts of sea level rise.