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Coastal flooding

Defra; MOHC; University of Southampton

  • Increased flood risk, from both rivers and the sea, is one of the most significant predicted impacts of climate change in the UK.
  • An increasing trend in extreme water levels has been observed and is most likely to be a consequence of the rise in average sea level.
  • Further rises in sea level over the next 100 years will tend to increase the frequency of extreme high-water-level events.
  • Future changes in storminess may alter the frequency of extreme high-water-level events, but the precise effects are uncertain and will depend on location.

Storm surges are short-lived increases in local water level, above that of the tide. They are driven by low atmospheric pressure and winds, typically in shallow seas. If they occur at or near a high tide large surges are liable to cause flooding.  Previous extreme surge events, such as that during the Winter of 1953, have led to a considerable loss of life and damage to property around the coastline of the southern North Sea.

An increasing trend in extreme water levels has been observed and is most likely to be a consequence of the rise in average sea level. Future extreme flood events may become more common as a result of increases in local relative time average sea level or altered atmospheric storminess, which could change the storm surge characteristics. The predictions presented in the UKCIP02The UKCIP02 climate change scenarios, prepared for the UK climate impacts programme and published in 2002, present four different descriptions of how climate may change, based on four different emission scenarios. analysis show the increase in the height of a flood event with a 50-year return period might be more than 1m during the 21st century at some locations. Most locations were predicted to experience a smaller increase. Comparison of the UKCIP02 results with other studies suggests that the pattern of increases in storm surge height is currently very uncertain and our confidence in being able to accurately predict the changes in extreme water level events is low. Research is underway to improve this situation by using ensembles of model simulations to better quantify the range of uncertainty. These new results will be made available as part of UKCIP08UKIP08 is the next climate change information package for the UK, consisting of five reports and an interactive website. The project brings together climate science from the Met Office to provide information to decision makers, academics and others, on the current climate, and possible future changes. Its interactive website will provide customisable climate change projections when it is launched in late 2008.. The UKCIP08 results, along with the IPCC 4th assessment report results, will form part of the evidence base that Defra will consider in the future to update it's advice on climate change impacts on the coast. The UKCIP08 new results aim to provide probabilistic information for business planning and longer-term development at the coast.

What is happening now - Low

What could happen in the future - Low

See executive summary

Coastal flood risk is a function of the probability of coastal flooding and the consequential damage, and hence depends on both the exposure of assets to flooding, and the standard of defences that exist. Presently, coastal flood risk is estimated to be about 50% of the national flood risk in England and Wales, with average annual damages of £0.5 billion. In the Foresight analysis, scenarios of potential changes in coastal flood risk due to changes in climate, society and the economy over the 21st century were analysed using a national-scale quantified flood risk analysis methodology (Hall et al., 2006; Thorne et al., 2007). Assuming that there is no adaptation to increasing coastal flood risk, the expected average annual damage in England and Wales due to coastal flooding is predicted to increase by two to 25 times to £1.0 and £13.5 billion. The great uncertainty reflects the range in the scenarios of climate and socio-economic change. Importantly, the proportion of national flood risk that is attributable to coastal flooding is projected to increase in all cases to between 60 and 70% of the total flood risk. Adaptation options including construction of coastal dikes or retreat from coastal floodplains were also analysed. These adaptations are shown to be able to reduce coastal flood risk to between £0.2 and £0.8 billion. The capital cost of the associated coastal engineering works is estimated to be between £12 and £40 billion. Non-structural measures to reduce risk can make a major contribution to reducing the cost and environmental impact of engineering measures and this strengthens the importance of linking planning with shoreline management.

Karl Hardy
Flood Management Division, Defra, Quantock House, Paul Street, Taunton, TA1 3NX

Robert Nicholls
University of Southampton, School of Civil Engineering and the Environment   Highfield, Southampton, SO17 1BJ

Jason Lowe
Hadley Centre for Climate Prediction and Research (Reading Unit), Meteorology Building, University of Reading, Earley Gate, Reading RG6 6BB