EEA - European Environment Agency

11/18/2021 | Press release | Archived content

Extreme sea levels and coastal flooding

Extreme sea levels and coastal flooding

Extreme sea levels have increased at most locations along the European coastline. Both observed and projected increases can be explained mainly by increases in mean local sea levels. However, extreme sea levels can be further increased by storm surges and tidal changes, particularly along the northern European coastline. In the absence of better coastal protection, the sea level rise projected for 2100 will increase the frequency of extreme coastal flooding events by a factor of 10 to more than 1 000 along most European coastlines, depending on the location and the emissions scenario.

Published: 18 Nov 2021 13:15‒ 25min read

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 10-cm rise in sea level typically increases the frequency of flooding to a given height by a factor of approximately three. 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 changes in coastal morphology. Changes in mean local sea levels are the main driver of observed and projected changes in extreme sea levels along the European coastline. However, changes in wave and storm surge climate may also play a substantial role in the changes in extreme sea levels in some European regions. Storm surge levels are projected to increase along the northern European Atlantic coastline, while projections suggest a mixed picture south of 50 °N. Notable increases in high tide levels are projected for the northern part of the Irish Sea, the southern part of the North Sea and the German Bight, whereas decreases are projected for the western English Channel.

By 2100, historically 1-in-100-year coastal floods are projected to occur at least once a year along the Mediterranean and Black Sea coasts and at least once a decade along almost all remaining European coasts, even under a low emissions scenario. Under a high emissions scenario, 1-in-100-year coastal floods are expected to occur at least once a year along most European coasts.

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 a recent output of the ECLISEA (European advances on climate services for coasts and seas) project.

Supporting information

Definition

This indicator reports changes in the frequency of historically 1-in-100-year floods along the European coastline. Such floods are caused by extreme sea levels, particularly during storm surges.

Methodology

Methodology for indicator calculation

Changes in the frequency of coastal flooding are calculated by comparing the observed distributions of extreme high sea levels at European tide gauges, based on the GESLA-2 data set, with projected distributions under various climate change scenarios. These model projections consider changes in local mean sea levels as well as changes in the storm, wave and tidal characteristics expected to occur as a result of climate change.

Uncertainty in future projections of extreme sea level 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 in 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 uncertainties

Methodology uncertainty

Not applicable.

Data sets uncertainty

No uncertainty has been specified.

Rationale uncertainty

No uncertainty has been specified.

Data sources and providers Institutional mandate

Metadata

DPSIRImpactTopicsClimate change adaptationWater and marine environmentTagsFlood riskClimate changeCLIM045Extreme eventSea levelGlobal warmingFloodingTemporal coverage
2010-2100
Geographic coverage
  • Albania
  • Austria
  • Belgium
  • Bosnia and Herzegovina
  • Bulgaria
  • Croatia
  • Cyprus
  • Czechia
  • Denmark
  • Estonia
  • Finland
  • France
  • Germany
  • Greece
  • Hungary
  • Iceland
  • Ireland
  • Italy
  • Latvia
  • Liechtenstein
  • Lithuania
  • Luxembourg
  • Malta
  • Montenegro
  • Netherlands
  • North Macedonia
  • Norway
  • Poland
  • Portugal
  • Romania
  • Serbia
  • Slovakia
  • Slovenia
  • Spain
  • Sweden
  • Switzerland
  • Turkey
  • United Kingdom
TypologyDescriptive indicator (Type A - What is happening to the environment and to humans?)UN SDGsUnit of measure
  • Frequency amplification factor of historical 1-in-100-year extreme sea level event.
  • Return period (years).
Frequency of disseminationEvery 2 yearsContact[email protected]

References and footnotes