Extreme sea levels and coastal flooding in Europe

Extreme sea levels have increased at many locations along European coastlines, due to increases in mean local sea levels. These ongoing increases will amplify the frequency of 1-in-100 years historical extreme events, by exposing most locations to critical conditions already with a sea level rise value above 10cm. In the absence of better coastal protection, the projected sea level rise would increase the frequency of extreme high coastal water levels by a factor of 10 in most European coastlines prior to 2050, with differences depending on the location and the future climate scenario.

Requested sea level rise for an amplification factor of 10 and 100 times

Increasing coastal flooding risks are threatening the achievement of a climate-resilient Europe, as aimed for by the EU strategy on adaptation to climate change.

Extreme sea levels can occur during storms and this can lead to coastal flooding in the absence of sufficient coastal protection. A 10cm rise in sea level typically increases the frequency of flooding to a given height by a factor of approximately 10. Extreme sea levels along coastlines result from a combination of factors, including increases in local mean sea levels and tidal levels, storm surge events, waves and local flood protection standards. Changes in mean local sea levels are the main driver of observed and projected changes in extreme sea levels along the coastline. The melting of glaciers and icesheets along with ocean thermal expansion being the most relevant processes impacting Europe’s seas.

The historically 1-in-100-year coastal floods are projected to increase by a factor of 10 before the year 2050 in many locations along the Mediterranean and Atlantic coasts, and along almost all remaining European coasts by the end of the century, under a low emissions scenario (CMIP6: Coupled Model Intercomparison Project Phase 6, SSP: Shared Socioeconomic Pathways). Under a high emissions scenario, 1-in-100-year coastal floods are expected to occur at least once a year along most European coasts before the year 2050, with some exception due to the already available flood protection measures.

Timing of occurrence of a 10 times amplification of the 1-in-100 years historical extreme in CMIP6 future projections

The concurrence of high sea levels and heavy precipitation resulting in large run-off volumes may cause compound flooding in low-lying coastal areas, as was the case in the catastrophic floods in Venice in November 2019. Currently, the Mediterranean coasts are at the highest risk of compound flooding. A recent study projected that climate change will increase the risk of compound flooding along most European coastlines, with the largest increases being expected along the North Sea and Baltic Sea coasts.

The planning of coastal protection at local and regional levels requires more detailed analysis of coastal flood risks than is currently possible at the pan-European level. A comprehensive overview of relevant data sets is available from the output of the ECLISEA (European advances on climate services for coastal services) project.

Supporting information

DefinitionMethodology

Methodology for indicator calculation

The frequency of coastal flooding historical extreme events are calculated using a probabilistic approach from the high-frequency tide gauge observations distributed along European coast of the GESLA-3 dataset, accounting for the estimated flood protection standards at different locations . Relative sea-level projections from IPCC AR6 (Garner al., 2021) up to 2150 for a range of Shared Socioeconomic Pathway (SSP) scenarios are used in combination with the estimated projections amplification factors (AFs) to determine the timing of changes in the frequency of extreme sea levels due to sea level rise. The amplification factor is the projected probability increase of a certain extreme sea level, which indicates the ratio between the future and historical probability of that extreme sea level. For example, an amplification factor of 10 by year 2050 indicates that a 1-in-100 years extreme event that has a 1% chance of occurring under present climate conditions will have a 10% chance of happening from year 2050 onward.

Uncertainty in future projections of extreme sea levels for Europe remains high and is ultimately linked to the uncertainty around future changes in mid-latitude storminess. Scientific understanding is advancing quickly in this area, as climate model representations of northern hemisphere storm track behaviour are showing improvements associated with, for instance, greater ocean and atmosphere resolution. However, the most recent global climate models have typically not yet been downscaled to suitably fine scales and used in studies of future storm surges.

Methodology for gap filling

Not applicable.

Methodology references

No methodology references available.

Policy/environmental relevance

Sea level rise can have significant impacts on settlements, infrastructure, people and natural systems. In Europe, the potential impacts of sea level rise include flooding, coastal erosion and the submergence of flat regions along continental coastlines and on islands. Low-lying coastlines with high population densities and small tidal ranges are most vulnerable to sea level rise and coastal flooding, particularly where adaptation is hindered by a lack of economic resources or other constraints. Currently, around 200 million people live along the coastal zone in Europe.

Damage associated with sea level rise is mostly caused by extreme events, such as storm surges. Of most concern is the coincidence of a storm surge with high tidal levels, leading to extreme sea levels. In Europe, the most intense surge events typically occur during the winter months. Furthermore, the concurrence of high sea levels and heavy precipitation resulting in large run-off volumes may cause compound flooding in low-lying coastal areas.

Accuracy and uncertaintiesData sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of dissemination

References and footnotes

EC, 2013, The EU strategy on adaptation to climate change, European Commission.

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Extreme sea levels and coastal flooding in Europe

Figure 1. Requested sea level rise for an amplification factor of 10 and 100 times

Figure 2. Timing of occurrence of a 10 times amplification of the 1-in-100 years historical extreme in CMIP6 future projections

Supporting information

Methodology for indicator calculation

Methodology for gap filling

Methodology references

Methodology uncertainty

Data sets uncertainty

Rationale uncertainty

Metadata

References and footnotes