Contributions to 21st century projections of extreme sea-level change around the UK

Tom Howard,Lucy M Bricheno,Matthew D Palmer

doi:10.1088/2515-7620/ab42d7

Tom Howard, Lucy M Bricheno + Show 1 more

Open Access

https://doi.org/10.1088/2515-7620/ab42d7

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Abstract

We provide a synthesis of results of a recent government-funded initiative to make projections of 21st century change in extreme sea levels around the coast of the United Kingdom. We compare four factors that influence future coastal flood risk: (i) time-mean sea-level (MSL) rise; (ii) changes in storm surge activity; (iii) changes in the offshore wave climate; (iv) changes in tidal amplitude arising from the increase in MSL. Our projections are dominated by the effects of MSL rise, which is typically more than five times larger than any of the other contributions. MSL is projected to rise by about 53 to 115 centimetres at the mouth of the Thames and 30 to 90 centimetres at Edinburgh (5th to 95th percentiles at 2100 relative to 1981–2000 average). Surge model projections disagree on the sign of future changes. Typical simulated changes are around +/−7 centimetres. Because of the disagreement, our best estimate is of no change from this contribution, although we cannot rule out changes of either sign. Wave model projections suggest a decrease in significant wave height of the order of 7 centimetres over the 21st century. However, the limited sample size and uncertainty in projections of changes in atmospheric circulation means that we cannot be confident about the sign of future changes in wave climate. MSL rise may induce changes in tidal amplitude of more than 15 centimetres over the 21st century for the Bristol Channel. However, models disagree on the sign of change there. Elsewhere, our projected tidal amplitude changes are mostly less than 7 centimetres. Whilst changes in MSL dominate, we have shown the potential for all processes considered here to make non-negligible contributions over the 21st century.

Highlights

For the UK, major coastal flood events are typically associated with wintertime storm surges that coincide with a high tide and high wave conditions
We have presented a synthesis of projections of 21st century change in sea-level extremes associated with changes in time-mean sea level (MSL), waves, tide and surge, developed for the United Kingdom Climate Projections 2018 Marine Report, and we have compared the sizes of these contributions
Our simulations show that projections of 21st century mean sea-level (MSL) change dominate over the sources which depend on changes in the storm tracks

Summary

Introduction

For the UK, major coastal flood events are typically associated with wintertime storm surges that coincide with a high tide and high wave conditions. There is concern about the effects of climate change on the future frequency and intensity of extreme coastal sealevel events. Climate change can give rise to increased coastal flood risk in two ways. The first is through an increase in time-mean sea level (often referred to as ‘mean sea level’, MSL), i.e. the baseline average water level on which tides, surges, waves and other sea-level extremes are superimposed. Menéndez and Woodworth (2010) showed that this component has dominated the changes in observed extreme water levels in the historical record

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