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Sea level rise was included to ensure the levels are relevant to base year 2017 and equates to increases in the order of approximately 2cm at most UK locations. Had the previous CFB levels not changed, base year 2017 levels would all be bigger than the 2011 published levels due to sea level rise differences between base years. However, improvements to the methodology and data has offset small changes in extreme sea levels due to sea level rise. These include:

• Significantly longer gauge records available in some areas than for the previous CFB. This can affect the magnitude of any given design level. (also slope of projections may be flatter – therefore low AEP events lower than previous CFB).
• Different methodology or process used to derive the levels.
• Detailed local study carried out since previous update.

More significant changes due to sea level rise are expected over longer return periods, for example to 2050 or 2100. Sea level rise should be taken into account when predicting flood risk in future years beyond 2017. Information on this is provided in the supporting documentation: Coastal flood boundary conditions for the UK: update 2018, User report.