Our coast in the future

The Crown Estate has been examining the potential impact of climate change on its Marine Estate. This feature demonstrates the potential impacts of climate changes leading to a sea level rise and a resulting increase in flooding risk. It examines the consequences for an area of land close to the shore at a point along the south coast of England.

On the following pages, you can see the changes as they would effect one stretch of coastline.

In creating this example, The Crown estate has drawn on the work of Haskoning UK Ltd and Professor David Pugh OBE. The data sets used include some provided by the Environment Agency and permission to use these is gratefully acknowledged.

Observed sea level is a combination of 3 components, the tidal level, the surge level and the mean sea level. This module will show the predicted effects of climate change on mean sea level and flooding risk as a result of the surge component being added to a higher mean sea level.

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The figure above shows the sea / land boundary at the mean sea level relevant to the year 2000.

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This figure shows the impact of the increase in mean sea level predicted for the year 2100, as a result of climate change. It is clear that a significant area of current land will be beneath the waves by 2100.

The calculations for the change in mean sea level are based on the predictions of the Intergovernmental Panel on Climate Change (IPCC), which at its 2007 meeting revised its estimate to suggest an increase of 0.47m in mean sea level over the century 2000-2100.

To this must be added a small component (approximately 0.6mm per year according to the UK Climate Impacts Programme) to allow for the continuing land subsidence along the south coast of England.

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Flooding in coastal areas is generally the result of a tidal surge above the mean sea level. There are various methods for calculating such surges, but they are based on meteorological observations over a period that are used to calculate the likelihood of a surge occurring.

Such calculations provide a ‘1 in several years’ prediction. The ”several years” can be any number of years, but typically from 10 years to 1000 years and this period is referred to as the ‘Return Period’. Thus a 1 in ten years flooding event has a Return Period of 10 years and a surge could happen every ten years.

The results of a series of these calculations can be represented as a graph of Flood level (in metres) against the Return Period (in years) and such a graph applicable to part of the south coast of England is shown on the screen above. The flood level in the graph is related to a standard reference or datum level, the Ordnance Datum Newlyn (ODN), but this is easily referenced to mean sea level at a particular point on the coast.

There are two lines on the graph, one labelled 2000 and the other (upper) line is labelled 2100.

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This Map is a repeat of the first in the series and shows the mean sea level in 2000. Subsequent screens will show the changes in land area at this location with different levels (risks) of flooding.

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This map shows the flooding for a 10-year return period based on the mean sea level in 2000. The flooded area can be distinguished from the original area of water at mean sea level.

The area of flooding depends on the variation in height of the land, with the low-lying land being flooded first. Therefore the extent of the flooding is specific to this location.

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This map is similar to the previous map, but with the addition of the change in extent of flooding for a 10-year Return Period predicted for 2100.

Clearly, the effect of climate change in increasing the extent of flooding for a particular flooding probability is very visible with a a larger area of the land being flooded.

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The next sequence of maps shows the changes in land area as a result of a flooding event with a 100-year return period. The above map is the starting point, showing the land area for mean sea level in 2000.

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This map shows the flooding for a 100 year return period based on the mean sea level in 2000. The flooded area can be easily distinguished from the original area of water at mean sea level. Again, the area of flooding is specific to this location.

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This map is similar to the previous map, but with the addition of the change in extent of flooding for a 100-year Return Period predicted for 2100. The effect of climate change in increasing the extent of flooding for a particular flooding probability is again very visible.

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This is a repeat of the earlier graph showing flood level against Return Period. It is useful to re-examine the detail of the two lines on this graph. By taking a flood level of, say 3.45m, the Return period in 2000 is ~350 years and for the 2100 line it is ~10 years. In other words, a flooding event in terms of land flooded, that in 2000 would only be estimated to occur once in ~ 300 years, will occur approximately once every 10 years in 2100. In other words; a flooding event which most people would not expect to see in their lifetime will, by 2100, be occurring typically once every 10 years.

This demonstrates the magnitude of the change in flood risks as a consequence of a change in the climate leading to an increase in the sea level. This emphasises the need to continually monitor the extent of climate changes and model its possible effects. This allows us to make the necessary changes, for example, in flood defences, building planning and land use and in lifestyle, that can minimise or reduce the risk to an acceptable level.

Acknowledgement

In creating this example, The Crown estate has drawn on the work of Haskoning UK Ltd and Professor David Pugh OBE. The data sets used include some provided by the Environment Agency and permission to use these is gratefully acknowledged.

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