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Coastal management in Cumbria

Objectives: Royal Haskoning undertook a study to support high-level coastal management decision-making at a site in Cumbria. It was commissioned to project future coastal recession and shore profile development.

UKCP09 products used: User Interface; Marine and Coastal Projections report

How were UKCP09 products used?

  • A Soft Cliff And Platform Erosion (SCAPE) numerical model was assembled to describe the local coastal profile, driven by local wave, water level and sea level rise conditions.
  • UKCP09 was used to estimate future change in surge, wave conditions, and relative sea level rise.

Sea Level Rise:

  • Both High and Medium emission scenarios were adopted to represent possible future climate.
  • H++ was rejected for this application as an extreme case, with low probability. 
  • The range of future sea levels to 2100 was then defined as between the lower limit (5th percentile) of the Medium scenario and the upper limit (95th percentile) of the High scenario.
  • A distribution was then assumed between these limits, to provide quartiles, and so define a central band of probability.
  • This band provided four trajectories of sea level rise, which were then used to drive the model.

Storm Surge:

  • UKCP09 projected very small growth in surge, but with a high uncertainty, consequently surge was explored through a range of sensitivity tests (i.e. without attempting to assign a probability function).

Waves:

  • UKCP09 projected a slight fall in wave conditions, but given wide associated uncertainty it was decided to assume no future change.

Difficulties & limitations

  • The sea level rise projections were too short for this study, and so had to be extended using other work. The timeframes of this study are exceptionally long; however coastal management typically works on a 100-year timeframe, whilst UKCP09 projects over the next 90 years.
  • The uncertainty (range) associated with the sea level projections is extremely wide. This is undoubtedly a reflection of uncertainty in the underlying science, however it does generate difficulties.
  • The Marine and Coastal Projections report does not provide distributions for the sea level rise projections. They are presented with a mid line, which is positioned half way between the 5% and 95% curves. This almost implies a symmetric distribution, which seems rather unrealistic.
  • The amount of information on storm surge and wave conditions was very limited, due to the small number of model simulations on which they were based. However, this was explained and interpreted well in the UKCP09 documentation.

Lessons learned

  • The interpretive information provided around the projections seems very good.
  • The projections used seem quite vague, with large uncertainties which pass into any subsequent analysis. Although upper and lower limits are provided, the range is around 80% of the maximum. In this example this necessitated additional interpretive work on the part of the user. These problems could be reduced if distributions of sea level rise could be provided. This would allow the user to chose alternative levels of confidence and focus on the most likely part within the range.
  • In this study the wide ranges passed into the predictions of future recession, although in a non-linear way. The results were less sensitive to uncertainty in the higher sea level rise projections.
  • The probabilistic nature of UKCP09 introduces challenges in that it forces the projection of ranges or distributions of future conditions, rather than a singular future (as for example is obtained when using the single sea level curve currently recommended by Defra). This has the knock-on effect that more results need to be generated and explained, along with their probabilistic basis.

The opportunity presented by the use of UKCP09 seems to be:

  • Employing the output of an extensive research effort.
  • Having a more realistic vision of the future than is provided by deterministic projections.
  • Uniformity and consistency; as different studies adopt UKCP09's authoritative views of the future their outputs could be compared and integrated.

How will the results be communicated to the target audience?

The work has been communicated in a formal report and through a series of presentations.

Find out more

  • Contact details: Dr Mike Walkden, Royal Haskoning.

  Download the Royal Haskoning case study report [4Mb]