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Sea level rise, extreme weather events and erosion

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Coasts, deltas, estuaries, lagoons, enclosed seas, and arctic coasts are vulnerable coastal systems that are affected by sea level rise, storm events and erosion. All of these types of coastal systems need to be considered when analyzing the impacts of climate change.

Introduction

European examples of areas likely to be affected by climate change include the London and the Thames estuary, Venice and the Venice lagoon, and the enclosed seas of the Adriatic, Mediterranean, Baltic and Black Seas. Representative examples of these vulnerable coastal ecosystems can be used as indicators of climate change, and to further understand approaches to and effectiveness of adaptation and mitigation strategies for climate change.

For the coasts, infrastructure and development, sea level rise will continue as an issue well into the future. It is interesting to note the shared and high vulnerability of lagoons, estuaries, deltas and arctic coasts to sea level rise, as well as storm surges and other extreme weather events. Given the extensive research as well as the high vulnerabilities within Europe, there are very relevant examples within Europe.

London and the Thames Estuary

London and the Thames Estuary are vulnerable to sea level rise, storm surge, flooding in the upstream tributaries of the Thames Rivers, and heavy rainfalls. All these factors and potential negative impacts have been aggravated by increased building in the flood plain, decreasing the absorption of rainfall and inadequate sewage and storm water drainage systems. In its period of operation, the Thames Flood Barrier has been used to reduce the impact of upstream flooding as well as tidal surges. An extensive study is now occurring under the Thames 2100 initiative to determine additional flood and tidal surge defence mechanisms that will be needed in the near future to address climatic sea level rise and extreme weather events. London and the Thames Estuary are currently protected to a high standard (generally 1:1000 years or 0.1% at the year 2030). The design of the Thames Barrier allowed for sea level rise but did not make any specific allowance for changes due to climate change in fluvial flows coming down the Thames or the size of storm surges arising in the North Sea. Rising sea level and rapidly increasing development within the tidal flood plain mean that flood risk is increasing and by the year 2030, improved arrangements will be required if flood protection standards are to be maintained at present levels.

Venice Lagoon and Central Portugal

Two other examples are the Venice lagoon and the central coastal region of Portugal. The Venice lagoon, the infrastructure and the communities are very vulnerable to sea level rise and storm events, with natural and human-induced vulnerability increased by climatic changes. Venice is not only threatened by high tides, but is sinking through subsidence, at the same time as the Adriatic Sea is rising. The surrounding marshes, which used to break the waves coming into the city, have gradually disappeared, and industrial development on the mainland has added to the increased subsidence and pollution.

Venice and the Venetian lagoon, of which the city is one integral part, are vulnerable to both extreme weather events and "normal" flooding, which now occurs up to 10 times in one year. Due to the subsidence of the lagoon (human induced and geological), as well as overall subsidence in the Adriatic Sea, Venice and the Venetian lagoon are also vulnerable to even a 10 centimetre increase in sea level, and will be dramatically affected by a large increase in sea level. The Moses project, which is comprised of 9 barriers, was approved in 2003, is now estimated to cost more than 5 billion euros, and is designed to rise from the seabed to block the inlets of the Venice lagoon from the Adriatic Sea when high tides are forecast. Given the sensitivity of Venice and the overall lagoon to climate change, it could also be considered as a model and indicator for global impacts of climate change for lagoons and coasts.

Coastal erosion is affected by extreme weather events, which can have major and catastrophic events on certain coasts. Some changes in sediment deposit may be amplified by climate change, such as a loss of sediment in storm events. In addition to extreme weather events, coasts may be eroded due to changes in sediment deposit, removal due to the construction of offshore structures and alterations of rivers through dams and diversions, resulting in changes in water flows and sediment deposition. Changes in sediment deposits results from changes in water flow due to a number a reasons. These include: the construction of dams on upstream rivers and watersheds, the removal of natural coastal habitats (i.e. wetlands), the construction of coastal structures and defences and the construction of offshore structures.

The Atlantic coast of central Portugal and settlements such as Aveiro and Figueira da Foz are very vulnerable to combination of climatic changes and coastal erosion, storm events, and changes in sediment deposit due to coastal dikes, groynes and upstream dams. Due to its depth, and absence of replenishing sediment deposits, the Venice lagoon can be impacted by shallow wave actions.

References

Case Study: Climate Change and European Coast and Beach Management, 2006, Completed by M.A.K.Muir for EU-funded Coastal Practise Network (CoPraNet)
The main author of this article is Magdalena Muir
Please note that others may also have edited the contents of this article.