Panagiotis Athanasiou, Ap van Dongeren, Alessio Giardino, Michalis I. Vousdoukas, Roshanka Ranasinghe, Jaap Kwadijk
Work Package 4
Sea level rise is a major problem for coastal communities and is predicted to worsen as the climate warms. This study assesses the likely shoreline retreat on sandy shores caused by future sea level rise, using a new approach which incorporates datasets of sandy shoreline location and slope. The team found that sandy shorelines in Europe may retreat by 54 m on average by 2100 compared to 2010 if future emissions are moderate, but by 97 m with high future emissions. This translates into coastal land loss of 1,400 km2 and 2,500 km2 respectively. Using the comprehensive datasets also allowed the team to identify hotspots, including the Italian Adriatic, the French Atlantic coast, parts of the North Sea and the eastern Baltic, which are particularly vulnerable to shoreline retreat. These results provide a greatly improved picture of how sea level rise may threaten Europe’s sandy shorelines in the future, while giving new insights into the associated uncertainties, allowing policymakers to enact measures to protect coastal communities from the impacts of climate change.
Sea level rise is a clear and obvious hazard associated with climate change and a serious problem for coastal communities. Sandy shorelines are particularly threatened as their shape and development are highly dynamic, leaving them vulnerable to shoreline retreat. These coasts have important ecological and touristic value, as well as protecting local communities from storm impacts. Up to now, large-scale assessments of shoreline retreat have used simple assumptions and generalisations, potentially leading their conclusions to be adversely affected by this over-simplification. This study addresses this problem, using more detailed datasets of the spatial distribution and slope of sandy beaches around Europe to quantify the threat that shoreline retreat poses in the region and the uncertainties in these estimates.
The team found that with moderate future greenhouse gas emissions (RCP 4.5) European sandy shorelines would retreat by 54 m on average by 2100 compared to 2010. This translates to a loss on 1,400 km2 of coastal land area. High future emissions (RCP 8.5) would lead to an even greater average retreat of 97 m and 2,500 km2 of coastal land lost. Both these scenarios are in the absence of any other changes to the shoreline position such as sediment deposition. Further analysis demonstrates that the choice of datasets for sandy shore location and slope in the coastal land loss projections can contribute up to 45% of the total variance for 2050 projections and up to 26% for 2100 projections, figures as high as those associated with the choice of future mitigation scenarios and different sea level rise projections. The datasets also revealed several coastal land loss hotspots around Europe, such as the Italian Adriatic, the French Atlantic coast, the eastern Baltic and parts of the North Sea, that previous methods were insufficient to identify.
This study utilised two different datasets of the spatial distribution of sandy beaches, one from the EUROSION initiative and one derived from satellite imagery. These were used in conjunction with a global dataset of nearshore slopes, a new approach leading to greater accuracy in the final simulations. This was also compared to the previously used method of assuming a uniform 1:100 slope for all sandy shorelines. The impact of sea level rise on these shorelines was assessed using the Bruun Rule, which accounts for various features of the shoreline profile both above and below the water line, including the slope, and assumes that an equilibrium profile will be maintained in the feature. Shoreline retreat was assessed at a 1 km spacing around the European coastline under moderate (RCP 4.5) and high (RCP 8.5) emissions scenarios, simulating changes by 2100 compared to a baseline year of 2010.
The results of this study have clear relevance to policymakers, highlighting the importance of accurate geophysical datasets and observational programs for the representation of the coast and providing a better understanding of the future of Europe’s sandy shorelines, helping identify the areas most at risk. This helps local and national authorities put in place policies to protect vulnerable coastal communities from the impacts of climate change.
Sea level rise (SLR) will cause shoreline retreat of sandy coasts in the absence of sand supply mechanisms. These coasts have high touristic and ecological value and provide protection of valuable infrastructures and buildings to storm impacts. So far, large-scale assessments of shoreline retreat use specific datasets or assumptions for the geophysical representation of the coastal system, without any quantification of the effect that these choices might have on the assessment. Here we quantify SLR driven potential shoreline retreat and consequent coastal land loss in Europe during the twenty-first century using different combinations of geophysical datasets for (a) the location and spatial extent of sandy beaches and (b) their nearshore slopes. Using data-based spatially-varying nearshore slope data, a European averaged SLR driven median shoreline retreat of 97 m (54 m) is projected under RCP 8.5 (4.5) by year 2100, relative to the baseline year 2010. This retreat would translate to 2,500 km2 (1,400 km2) of coastal land loss (in the absence of ambient shoreline changes). A variance-based global sensitivity analysis indicates that the uncertainty associated with the choice of geophysical datasets can contribute up to 45% (26%) of the variance in coastal land loss projections for Europe by 2050 (2100). This contribution can be as high as that associated with future mitigation scenarios and SLR projections.