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Indicator Assessment

Extreme sea levels and coastal flooding

Indicator Assessment
Prod-ID: IND-346-en
  Also known as: CLIM 045
Published 23 Feb 2021 Last modified 23 Feb 2021
1 min read

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.

Change in the frequency of flooding events in Europe given projected sea level rise under two climate scenarios

Note: This maps show the estimated change in the frequency of flooding events of a given height between 2010 and 2100 due to projected regional sea relative level rise under the RCP2.6 and RCP8.5 scenarios. Values larger than 1 indicate an increase in flooding frequency. RCP, representative concentration pathway; RCP2.6: low emissions scenario; RCP8.5: high emissions scenario

Data source:

Increasing coastal flooding risks are threatening the achievement of a climate-resilient Europe, as aimed for by the EU Strategy for 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 (Weisse et al., 2014; Marcos and Woodworth, 2017; Vousdoukas et al., 2017; EEA, 2020; Kirezci et al., 2020). 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 (Vousdoukas et al., 2016, 2017). 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 (Idier et al., 2017; Pickering et al., 2017).

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 (Vousdoukas et al., 2017, 2018; Oppenheimer et al., 2019). 

Return period of current 100‐year extreme sea levels under two emissions scenarios

Note: Solid coloured boxes show the ensemble mean value and coloured shading shows the inter‐model variability (from worst to best case). The mean value for the entire European coastline and values for the coasts of 10 geographical regions are shown. N-North, northern part of the North Atlantic; S-North Atlantic, southern part of the North Atlantic; RCP, representative concentration pathway; RCP4.5: medium emissions scenario; RCP8.5: high emissions scenario

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 (Bevacqua et al., 2019).

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 (Acevedo et al., 2018).

Supporting information

Indicator 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.

Units

  • Frequency amplification factor of historical 1–in–100 year extreme sea level event
  • Return period (years)

 

Policy context and targets

Context description

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Targets

No targets have been specified

Related policy documents

No related policy documents have been specified

 

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 (Woodworth et al., 2016a, 2016b), 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.

 

Uncertainties

Methodology uncertainty

Not applicable

Data sets uncertainty

No uncertainty has been specified

Rationale uncertainty

No uncertainty has been specified

Data sources

Other info

DPSIR: Impact
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CLIM 045
Frequency of updates
Updates are scheduled every 2 years
EEA Contact Info info@eea.europa.eu

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Geographic coverage

Temporal coverage

Dates