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Environmental information systems
Driven by rising sea levels, tidal swings and storm surges, coastal floods are a growing threat to buildings, energy and transport infrastructure, water supplies and human lives. Coastal defences (walls, breakwaters, artificial headlands) are generally designed to withstand sea levels within historical ranges (e.g. ‘once-in-a hundred-years’ floods). Projected changes in the frequency and intensity of coastal floods are a major threat to ecosystems and the population in low-lying coastal areas in northern and western Europe.
Key messages
Increases in mean local sea levels are the main driver of observed and projected increases in extreme sea levels along the European coastline.
With some limitations to the data, historical once-in-a-hundred-years coastal floods are projected to occur several times a year on the Mediterranean Sea and the Black Sea coasts, at least once a year along most other European coasts under a high-emissions scenario and at least once a decade along the remaining European coasts even under lower emissions scenarios.
The only exception is the northern Baltic Sea, where current coastal floods are projected to become rarer as a result of continued land uplift following the last ice age.
Extreme sea level
Definition
The extreme sea level index represents the maximum sea water level along the coast corresponding to a 1-in-100-year coastal flood event.
Index factsheet (ETC/CCA Technical Paper): Extreme sea level
Relevance
This index is relevant for a wide range of applications in coastal regions, including regional planning, infrastructure design, coastal protection and ecosystem management.
Past and projected changes
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.
The past and projected changes in maximum sea water levels corresponding to 1-in-100-year events are not currently covered by a C3S data set. However, the projected changes in annual highest high water and in the frequency of 1-in-100-year coastal floods are available in the European Climate Data Explorer and in an EEA indicator assessment, respectively (see below).
As a result of the relative sea level rise projected by 2100, historical 1-in-100-year coastal floods are projected to occur several times a year along the Mediterranean and Black Sea coasts and at least once a year along most other European coasts under a high-emissions scenario (representative concentration pathway (RCP)8.5), and at least once a decade along the remaining European coasts even under the lowest emissions scenarios. The only exception is the northern Baltic Sea coast, where current coastal floods are projected to become rarer as a result of continued land uplift following the last ice age.
Note that the application of this index at the regional and local levels requires the integration of index information with regional information on land subsidence and coastal protection infrastructure.
Further information (European Climate Data Explorer): Annual highest high water, 2070-2100
Further information (EEA indicator assessment): Extreme sea levels and coastal flooding
Projected changes in the frequency of historical 1-in-100-year coastal floods
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Return period of current 100-year extreme sea levels for European coasts
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