Sea level rise will challenge adaptation responses regionally and worldwide. The largest impacts will be on flat low-lying coastlines, such as around parts of the UK. With a 1°C temperature rise, a 3 m sea level rise is locked in over the 21st and 22nd centuries; 1.5°C around 5 m; and 2–3°C, 10–20 m of sea level rise. Slowing the rate of greenhouse gas emissions will slow the rate of sea level rise, giving communities time to respond and adapt. However, the accompanying climate change is resulting in increased frequency and magnitude of storm events, which result in lateral erosion of the coastline.

Over the past decade, storms have repeatedly subjected large areas of the coast to enormous stress and caused extensive damage. Coastal flooding happens because of a combination of high tides, storm surges and waves. A storm surge is a temporary large-scale rise in sea level caused by strong winds pushing water towards the coast where it ‘piles up’, and by low pressure at the centre of storms – this ‘pulls’ the sea surface up by about 1 cm for every millibar that air pressure drops. Coastal protection schemes have defended the coastline with ‘hold the line’ policies and ‘hard’ defences, such as sea walls and groynes, but these will become increasingly financially untenable with rising sea levels and higher storm surges.

Proposed managed realignment involves the deliberate breaching of hard defences to create more intertidal habitats to buffer wave energy and reduce hard defence costs. But how coastal wetlands will respond to rising sea levels and increasing storm surges is poorly understood. While some coastal saltmarshes (such as in the Thames Estuary) are thought to be more resistant to such erosion, others (such as those fringing Morecambe Bay) have experienced dramatic erosion and coastal retreat in recent years (200 m of coastal retreat in 10 years for parts of Morecambe Bay).

Consequently, understanding the factors that drive the resilience of coastal wetlands to lateral erosion will be a critical element in assessing current and future vulnerability to low-lying coastal communities and may become a devolved issue, with policy responsibility held by Defra, the Welsh Government, the Scottish Government and the Northern Ireland Executive. However, the measures are implemented through shoreline management plans developed by maritime local authorities (there are 22 shoreline management plans for England).

A POSTnote on this subject will summarise emerging evidence and its implications for coastal flood risk management.

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