Do storms cluster, and what does this mean for coastal hazards around the UK?
Written by Dr Doug Pender | Principal Engineer

Coastal management and planning have long focused on making decisions that combine both the short and long-term impacts of flood and erosion risk. With the realisation that we can no longer defend against climate change impacts, we must change how we approach these practices. To be practical and sustainable, this requires a greater understanding of hazards on intermediate (seasonal to decadal) time scales. In turn, there is a need to maximise the reliability of existing assets, work with natural processes and changes, and embed these into confident and robust decisions. This will increase resilience, enabling communities to adapt and recover more sustainably from storms.

The 2013/14 winter highlighted the importance of clustering, when an average of one intense storm impacted the UK every two and a half days, resulting in aggregated impacts on the southwest coast. To better understand the frequency of clustering around the UK a collaborative research project is investigating this from several angles.

The first objective of the research was to explore coastal hazard clustering (storm surges, wave heights, and sea levels) around the UK. This was examined at interannual (between years) and intra-annual (within years) time scales, and utilised data from the UK’s coastal monitoring network, supplemented by longer, 40-year, modelled records.

To evaluate interannual patterns, exceedance counts were determined. For the intra-annual patterns, the time window was shortened and focused on days between exceedances. Both assessed spatial and temporal patterns, grouping results into coastal regions of similar characteristics.

The occurrence is not consistent through time and there are substantial periods with and without exceedances. This indicates a pattern not currently considered within typical FCERM practices but will increase in importance as we move to adaptive approaches. Within storm seasons, large proportions (up to 45%) occur within 50 days of each other. While this reduces with increasing intensity, the pattern is still evident. A rapid increase in clustering should be expected as sea levels rise. Overall, while there is relative geographical consistency, the North Atlantic and Bristol Channel are more susceptible, with the North Sea the least so. This is perhaps unsurprising given the prevalent meteorological climate but helps guide where clustering assessments should be prioritised.

While it is easiest to see the relevance of clustering on the impact on beaches there are wider implications. These range from increased maintenance costs, higher levels of community distress, or multiple insurance payouts.

What does this mean moving forward?

It is now known that coasts are likely to face multiple hazard exceedances in stormy years. The increase in prevalence due to sea-level rise shows clustering is important and should be understood and translated to increase community resilience and promote sustainable adaptation.

What does this mean in practice?

We must understand more about the impacts of clustering on coastal systems and weigh up these risks to focus on robust intermediate decisions. This is critical to allow for fast, effective, post-event actions to be taken.

How should it be achieved?

It should adopt a practical angle that builds on this learning to consider impacts. Partnership working and collaboration are key, and these initial successes should be used to support decision-making by practitioners, including the Environment Agency.

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Want to know more?

For more on our Marine and Coastal Risk Management expertise, please contact Dr Doug Pender.

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