Likely and High-End Impacts of Regional Sea-Level Rise on the Shoreline Change of European Sandy Coasts Under a High Greenhouse Gas Emissions Scenario

Abstract

<p>Sea-level rise (SLR) is a major concern for coastal hazards such as flooding and erosion in the decades to come. Lately, the value of high-end sea-level scenarios (HESs) to inform stakeholders with low-uncertainty tolerance has been increasingly recognized. Here, we provide high-end projections of SLR-induced sandy shoreline retreats for Europe by the end of the 21st century based on the conservative Bruun rule. Our HESs rely on the upper bound of the RCP8.5 scenario “likely-range” and on high-end estimates of the different components of sea-level projections provided in recent literature. For both HESs, SLR is projected to be higher than 1 m by 2100 for most European coasts. For the strongest HES, the maximum coastal sea-level change of 1.9 m is projected in the North Sea and Mediterranean areas. This translates into a median pan-European coastline retreat of 140 m for the moderate HES and into more than 200 m for the strongest HES. The magnitude and regional distribution of SLR-induced shoreline change projections, however, utterly depend on the local nearshore slope characteristics and the regional distribution of sea-level changes. For some countries, especially in Northern Europe, the impacts of high-end sea-level scenarios are disproportionally high compared to those of likely scenarios.</p>

Uncertainties in Shoreline Projections to 2100 at Truc Vert Beach (France): Role of Sea‐Level Rise and Equilibrium Model Assumptions

“…Therefore, in addition to the Gaussian distribution reflecting the SROCC assessment (Oppenheimer et al., 2019), we consider a high‐impact, low probability high‐end sea level scenario that might take place for high greenhouse gas emissions (RCP 8.5; black line in Figure 4b) following the same assumptions as Thiéblemont et al. (2019) (see Text S2).…”

“… Probability distributions of: relative mean sea level over the period 2020–2100, including the likely (dark shaded areas) and 5–95th percentile (light shaded areas) ranges, for (a) RCP 4.5 and (b) RCP 8.5 scenarios, with deterministic high‐end sea‐level projections based on 2100 high‐end “highest‐modeled” estimates following Thiéblemont et al. (2019) (black line); (c) Gaussian distributions of depth of closure values calculated over the 2020–2100 wave time series for RCP 4.5 (blue curve) and RCP 8.5 (red curve) scenarios; and empirical joint probability distributions of (d) ShoreFor [ k s + , Φ] parameters, and (e) Yates [ k y +/− , a 1 , and a 2 ] parameters, obtained fitting a kernel density function (with bandwidths estimated from the marginal kernel density function for each variable) on 6,000 combinations of model parameters producing NS > 0.25 against shoreline data. …”

Climate change-driven coastal erosion modelling in temperate sandy beaches: Methods and uncertainty treatment

“…Open beaches are relatively long beaches (nearly) unprotected at their ends and where both cross-shore and longshore sediment transport are often essential components of the sediment budget. Current works at open beaches include the analysis of future wave-driven coastal sediment transport developed by Casas-Prat et al (2016); Rosati et al's (2013) and Dean and Houston's (2016) modified Bruun Rule formulations used to assess SLR-induced shoreline response (the latter also recently applied by Karunarathna et al, 2018); the approach proposed by Vitousek et al (2017) for predicting the shoreline evolution driven by longshore and cross-shore transport due to projected waves and SLR; the cross-shore model ensemble performed by Allenbach et al (2015); and the assessment of SLR-driven shoreline retreats along the European sandy coasts presented by Thiéblemont et al (2019). In addition, we include the studies presented by Le Cozannet et al (2016, which focused on quantifying uncertainty in future shoreline change.…”

“…At the European scale, Thiéblemont et al (2019) presented a first estimate of the contribution of regional SLR to coastal erosion on sandy coasts under likely and high-end sea-level rise scenarios by the end of the twenty-first century. The authors developed pan-European high-end scenarios based on the upper bound of the RCP8.5 scenario and on high-end estimates of global and regional components of sea-level projections considering their uncertainty (e.g., using a multi-model ensemble and the AR5/SROCC J o u r n a l P r e -p r o o f median and likely ranges).…”

Modelling Present and Future Climate in the Mediterranean Sea: A Focus on Sea-Level Change

“…In addition to the local dynamics and geological processes, interacting over a broad spectrum of scales, sea level in the basin is also constrained by the water mass exchange across the Strait of Gibraltar, which, in fact, regulates the hydraulic jump between the Mediterranean and the Atlantic Ocean and in uences In general, the inherent uncertainty in SLR projections has induced researchers to adopt a variety of alternative estimates in their impact assessments. Thiéblemont et al (2019) analyze the effects of a median estimate of about 80 cm and two different high-end scenarios, resulting from two extreme estimates for the sea-level equivalent of melting glaciers (i.e the the upper limit of the likely range and the "worst model" projections). Antonioli et al (2017), while reviewing possible alternative ranges for the projected high-end SLR at 2100, use the 530-970 mm interval reported in the IPCC AR5, and Rahmstorf's semi-empirical estimate of about 1.400 mm (Rahmstorf, 2007).…”