Storm Surges
One of the most common causes of coastal flooding are storm surges, which occur when strong winds and low atmospheric pressure cause sea levels to rise above normal. Storm surges can cause extensive flooding when they coincide with high tides, resulting in water levels breaching coastal defences or natural barriers.
In Wales, storm surges are often associated with winter storms, which can bring powerful winds and heavy rainfall, compounding the risk of both coastal and river flooding.
Sea-Level Rise
As a result of global climate change, sea levels are rising. This is a long-term trend that increases the baseline for coastal flooding. In Wales, sea-level rise is already noticeable, with projections suggesting further increases in the coming decades.
Even small increases in sea level can lead to more frequent and severe coastal flooding events, as higher baseline water levels mean less capacity for storm surges and high tides to be absorbed by the coast and any sea defences in place.
High Tides and Spring Tides
Tidal patterns can greatly influence the likelihood of coastal flooding. Wales experiences a significant tidal range, particularly in areas like the Bristol Channel.
During spring tides—when the sun and moon align to create higher-than-usual tides—the risk of flooding increases, especially if these high tides occur alongside stormy weather.
Heavy Rainfall and River Flooding
In addition to marine influences, heavy rainfall can exacerbate coastal flooding by swelling rivers that flow into the sea.
This is particularly a concern in Wales, where the steep, narrow valleys that characterize many coastal areas can funnel water into low-lying areas, leading to compounded flood risks at river mouths.
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This image shows a river in the Vale of Glamorgan that frequently floods neighbouring fields during spring tides.
What is a storm surge?
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A storm surge is an abnormal rise in sea level caused by strong winds and low atmospheric pressure during a storm. This rise in water level can result in flooding along coastlines, particularly when it coincides with high tides. Storm surges are a major cause of coastal flooding and can lead to extensive damage to coastal infrastructure and communities.
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Storm surges occur when strong winds, typically from an intense storm, push large volumes of water towards the shore. The force of the wind causes the water to pile up, while the low pressure in the storm’s centre further contributes by allowing the sea surface to bulge upwards. The height of a storm surge can vary, depending on factors such as the intensity of the storm, the shape of the coastline, and the sea depth.
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For more information and storm surge predictions for your nearest port, please click here.
How are the impacts of climate change affecting storm surges?
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In Wales, we are likely to see an increase in the frequency and intensity of storms due to climate change. This means that due to the increase in the number of low pressure systems and the increase in average storm wind strengths we are likely to see an increase in the frequency and height of storm surges.
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Additionally, as sea levels rise, the baseline water level is higher, meaning that even a moderate storm can cause significant coastal flooding. This allows storm surges to have a greater reach, affecting areas that previously might have been safe from flooding. Rising seas also reduce the natural buffer zones, like beaches and dunes, that protect coastal areas from storm surge impacts.
Impacts of Increased Storm Surges
The increase in storm surge frequency and intensity poses significant risks to coastal communities and ecosystems:
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Increased Flooding: Higher storm surges, combined with rising sea levels, can flood low-lying coastal areas more frequently, causing more damage to homes, infrastructure, and businesses.
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Coastal Erosion: Powerful storm surges can accelerate coastal erosion by removing large amounts of sand and sediment from beaches and dunes, undermining natural coastal defenses.
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Economic Damage: Storm surges can disrupt ports, transportation, and industries located near the coast, leading to significant economic losses.
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Ecosystem Disruption: Coastal habitats such as wetlands, mangroves, and estuaries are particularly vulnerable to storm surges. These areas provide important environmental services, such as carbon sequestration and flood protection, and their loss can have cascading effects on biodiversity and coastal resilience.