Over the past century, natural variations in storm frequency and magnitude over 10-20 year cycles have been the most important climatic factor driving coastal flood risk. However, changes in land use and movement of people and key services to coastal areas over this time period has generally increased vulnerability to coastal flooding.

Extreme sea levels in the future are likely to be dominated by climate driven changes to the mean sea level, rather than waves or storm surges. There is a great deal of uncertainty surrounding the magnitude of changes in mean sea level and wind waves (thus extreme events), but not the direction of change for mean sea level. This will increase the likelihood of coastal flooding. Without adaptation this will lead to significant losses to economic, social and environmental assets by the end of this century and beyond. Since sea level rise is committed to continue beyond 2100, even with immediate stabilisation of greenhouse gas emissions, then policy and adaptation measures require a strategy over a much longer period.

The direct effect is to increase the probability of inundation, although another factor is the increased risk of coastal defence failure due to increased loading. Any changes in the direction of major storm events could also alter patterns of coastal morphology and erosion. It has been estimated that a 40cm sea-level rise, which is broadly in line with UKCP09 projections by 2100 under a medium emissions scenario, would increase the number of properties at risk in eastern England from around 270,000 to 400,000. In the absence of adaptation measures, economic damage due to coastal flooding could become 0.2% of GDP by the 2080's.

What is already happening: High

Observational evidence for present day sea level (including land movement from GPS), storm surge and waves processes is of the highest quality. Present day flood risk (including exposure) is also quantified to a high degree of precision helped by numerical flood mapping and precision LIDAR shoreline data, so our understanding of what is already happening is high.

What could happen: Low

Projections of the future rely on the accuracy of (i) our projections of mean sea level combined with the uncertainty surrounding future surge and wave climates and (ii) estimates of coastal development and land use. Both of these are known poorly so our level of confidence for what may happen in the future is low. The projected trend in mean sea level has no uncertainty about its direction (despite a range of values for its rate) so an increased risk of coastal flooding has high certainty.

The top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers are:

1. A more complete examination of the future wave climate projected by the UKCP09 perturbed parameter ensemble, and that which may result from other climate models in the IPCC (2007) multi-model set
2. A reliable prediction of new coastal development, the siting of new infrastructure and the required level of protection
3. An integrated assessment of the potential flood losses arising from these projections, including ecosystem goods and services
4. Detailed scientific understanding of sediment transport processes and coastal morphology over long (decadal-centennial) timescales

There is wide agreement on these key challenges.

With the implementation of Marine Bills at both a UK and Scotland level, terrestrial and marine spatial planning will require co-ordination which may be assisted by existing non-statutory local coastal partnerships (established under principles of Integrated Coastal Zone Management - ICZM). Established in the early 1990s, these local voluntary partnerships have proved very successful in promoting multi-sector planning.

England and Wales

Evidence of increasing costs of coastal flood protection was provided by Burgess & Townend (2004), who estimated that by the 2080s the annual cost of new coastal defence structures will be between 150 and 400% of the current levels (depending on the emissions scenario). Costs were less sensitive to geographic location than to emissions scenario. The costs were predicted to increase because structures were found to be very vulnerable to increases in water depth. Non-structural measures, such as land use planning and flood warning, could also make a considerable contribution to reducing this risk though no attempt has been made to estimate the cost of these measures.

The Environment Agency's Long Term Investment Strategy ( http://www.environment-agency.gov.uk/research/library/publications/108673.aspx) does not provide separate analysis for coastal flooding, but the findings illustrate the increasing investment required to fully respond to climate change. Modelling of both river and coastal flood risk suggests that to sustain current levels of protection in the face of climate change requires an increase in investment from current levels of £570 million to more than £1 billion a year, plus inflation, by 2035. Conversely, keeping investment in building and maintaining defences at current (2010/2011) levels could increase the number of properties at significant risk by 350,000 (from 490,000 now to 830,000 in 2035).

At many coastal sites (including major industrial and infrastructure facilities) there is limited scope to retreat inland without major economic and/or social implications. The frequency and severity of loading of defences means that they will be increasingly costly to repair or replace. A reduction in sediment supply to the coasts will be reflected in a narrowing of beaches and deterioration in amenity and ecological value of coasts. Avoidance of these losses requires a long-term strategic approach to coastal zone management.

Shoreline Management Plans (SMPs) are the backbone of coastal management in England and Wales. They contain flood and coastal erosion risk management policies for 20, 50 and 100 years into the future. Currently, local authorities are revising 18 SMPs and the Environment Agency the remaining four, ready for 2010. The new SMPs will provide a 'route map' for local authorities and other decision makers to move from the present situation towards meeting future needs, and will identify the most sustainable approaches to managing the risks to the coast in the short term (0-20 years), medium term (20-50 years) and long term (50-100 years).
The broad objective of the Draft Flood and Water Management Bill, put before Parliament on 19th November 2009, is the management of water in ways that address future climate change risks. It responds to key recommendations from the Pitt Review ( http://archive.cabinetoffice.gov.uk/pittreview/thepittreview.html) and is the primary means of implementing the objectives set out in the Defra Making Space for Water Programme ( http://www.defra.gov.uk/environment/flooding/policy/strategy/index.htm) and the EU Directive on flood risk. The Bill also aims to embody the principles of Integrated Coastal Zone Management (ICZM), a process that seeks to join up the different policies, and increase "stakeholder" influence in coastal management through effective dialogue. ICZM is currently being promoted throughout the European Union.

Examples of adaptation for coastal flood and erosion management can be found at:  http://www.environment-agency.gov.uk/research/planning/108361.aspx

Scotland

Coastal flooding management policy in Scotland will be heavily influenced by the recent implementation of the EC Directive on Assessment and Management of Floods (the Floods Directive). This was put into law in 2009 by the Flood Risk Management (Scotland) Act. The Act expands the role of the Scottish Environment Protection Agency (SEPA) in risk assessment and planning, making it the lead authority for assessments of flood hazard and potentially vulnerable areas, and for drawing up flood risk management plans. Implementation of the Floods Directive is likely to be challenging at the coast, as hazard assessment requires quantification of the risk of extreme water heights, wave action, and the role of defences. A database of grant aided flood defence assets in Scotland has been compiled on a national level. However, there is still a general lack of data on flood defences and condition particularly those protecting infrastructure. Local databases will be established under the 2009 Act, which will be the responsibility of local authorities.

On Scotland's 'softer' coasts, susceptibility to erosion has often justified public funding for coastal protection. The resulting defences often provide ancillary flood management benefits (Ball et al., 2008). As in England and Wales, increasing rates of sea level rise and budget limitations call into question the future viability of defences, and lack of knowledge of sediment erosion and accretion rates along many parts of the coastline remains a key problem in planning for the future. SMPs in Scotland have regional coverage on coastlines where erosion is a management issue, and are valued in this respect by local authorities. They have identified some limited scope for targeted managed realignment which may have local flood risk management benefits in some locations. ICZM has been very effective in Scotland in bringing together voluntary stakeholder partnerships.

Ireland

A lack of underpinning knowledge is presently a compromising factor in developing socio-economic responses, and is a strengthening driver to further study. As a larger database of high quality observations becomes available, an improved understanding of the storm and wave climate around Ireland will enable demarcation of regions susceptible to projected changes.

Horsburgh, K., Ball, T., Donovan, B. & Westbrook, G. (2010) Coastal Flooding in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 10pp. www.mccip.org.uk/arc