Sandy beaches can survive sea-level rise

Vousdoukas et al. assert that global sea-level rise (SLR) poses a threat to the existence of sandy beaches. They use global databases of sandy beaches, bathymetry and wave conditions to drive a simple model based on the Bruun rule to quantify shoreline retreat, to which they add a background ambient trend based on satellite data. When retreat is more than 100 m by 2100, they declare those beaches near extinct by the end of the century. We feel that this is an incorrect and potentially damaging finding. Critical to the paper’s conclusions is the fact that, provided that accommodation space is available, beaches migrate landwards as sea level rises and shorelines retreat. Many contemporary beaches formed thousands of years ago and migrated landwards during postglacial SLR. Globally, hundreds of beaches have been retreating at rapid rates for more than a century, but have not been extinguished. In southwest France, for example, the shoreline has receded >100 m but still has wide and healthy beaches. The underlying premise of Vousdoukas et al. originates in an inappropriate model—the Bruun rule, in which SLR promotes offshore sediment transport. As stated in their methods: SLR-induced shoreline retreat “…depends on the amplitude of SLR and the transfer of sediment from the subaerial to the submerged part of the active beach profile”. While we agree that offshore sediment transport might happen in cases of very steep topography, in most cases sediment transport is onshore during SLR.