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

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 nonnegligible contributions over the 21st century.

Dynamical downscaling of unforced interannual sea-level variability in the North-West European shelf seas

“…Understanding the shelf sea level response to the wave and advective processes and their relationship to future changes to the shelf slope current is an interesting topic for future research. Changes in shelf sea level, particularly in the coastal regions, can affect the tidal propagation and can have an important impact on coastal sea level (e.g., Howard et al 2019;Haigh et al 2020).…”

Exploring the Drivers of Global and Local Sea‐Level Change Over the 21st Century and Beyond

“…This adjustment process gives rise to areas of upward and downward vertical land motion, and the associated mass redistribution also influences Earth's rotation and gravity field with additional impacts on local MSL. It is well known that GIA leads to substantial spatial variations in the rates of MSL change observed at tide gauges and, such as the lower rate of sea‐level rise seen for the north of the United Kingdom compared to the south (Howard et al, 2019; Palmer, Harris, et al, 2018). Since the adjustment time scales of GIA are thousands of years, we make the approximation that the contemporary rates of its effect on local MSL change are valid for the projections (i.e., the rates are assumed to be time constant).…”

Improving sea-level projections on the Northwestern European shelf using dynamical downscaling

“…Extreme sea levels and tides have mainly been studied with barotropic models (e.g. Sterl et al 2009;Howard et al 2010;Pickering et al 2012;Ward et al 2012;Pelling et al 2013;Pelling and Green 2014;Cannaby et al 2016;Idier et al 2017;Palmer et al 2018;Howard et al 2019). DSLC on the NWES however, has not extensively been studied with RCMs, with the exception of Mathis (2013) who analyzed the seasonal variation of 100-yr sea-level trends in the North Sea with the HAMSOM model.…”