Scotland and Ireland are being battered by larger and stronger waves during winter than 70 years ago

Thursday, 26th April 2018, 9:36 am
Updated Thursday, 26th April 2018, 10:36 am

Scotland and Ireland are being battered by larger and stronger waves during winter than 70 years ago, a new study found.

Since 1948 the average height of waves rolling in from the Atlantic during severe winter gales have increased by over five-and-a-half feet or 1.7 metres.

The Atlantic coastlines of Scotland and Ireland have borne the brunt seeing the greatest increase in wave height of western Europe.

Over the past seven decades the average height of winter waves have increased by more than 0.4 inches or one cm per year.

But during extreme weather conditions, levels off the Irish coast increased an inch or 2.5cm during the past 70 years, representing an average increase of 5ft 6in or 1.7m.

In contrast France's Atlantic coastlines only saw the average height of winter waves increase by 0.19in or 5mm per year and Portugal 0.04in or 1mm a year.

Scientists warn the increase in wave energy has implications for coast communities as beaches and dunes are washed away and cliffs collapse.

And when winter storms combine with high tides they can cause widespread inland flooding and damage as boulders are swept in.

They noted just one severe storm can cause widespread erosion than the cumulative impact of a series of winter storms.

And if the intensity of storms increases because of climate change communities must brace themselves for more frequent devastating winter storms such as in 2013 to 2014.

Opportunity for renewable energy

However on the positive side the increase wave power during winter could be a increasingly important source of renewable energy.

Dr Bruno Castelle, Senior Scientist at the National Centre for Scientific Research (CNRS) in France, said: "The height of waves during winter storms is the primary factor affecting dune and cliff erosion, explaining up to 80 per cent of the shoreline variability along exposed sandy coasts.

"So any increases in wave heights, and greater frequency of extreme storms, are going to have a major impact on thousands of communities along the Atlantic coastlines of Western Europe.

"This work and our other recent studies have shown both are on the rise, meaning there is a real need to ensure the Atlantic coasts of Europe are protected against present and future storm threats."

Dr Castelle explained: "Winter wave activity was greatly inﬂuenced by large-scale patterns of atmospheric and oceanic variability on interannual and longer timescales.

"Coastlines along western Europe, which comprises a wide range of low-lying and/o r populated regions, is exposed to high-energy winter waves generated in the North Atlantic Ocean.

"The North Atlantic Oscillation (NAO) is the dominant mode of atmospheric variability at mid-latitudes in the North Atlantic region, and it has therefore long been known that interannual to decadal variability of winter wave activity is strongly aﬀected by the NAO.

"However, the NAO primarily aﬀects winter wave height variability in the northern latitudes, say north of 50◦N."

The UK lies at 52◦N.

Waves off the coast of Skye. Shutterstock

Understanding the causes

Professor Gerd Masselink, Lead of the Coastal Processes Research Group at the University of Plymouth, added: "Whether extreme winters such as that of 2013/2014 will repeat more frequently and/or will further intensify in the future is a key issue for the coastal regions of west Europe.

"It is therefore important to investigate if these extreme winters are already happening with increasing regularity and increased intensity.

"If human-induced climate change is responsible, we need to seriously start thinking about decreasing our vulnerability to extreme storm events and pro-actively adapt to a more energetic future wave climate.

"Wave buoy measurements, satellite altimeter measurements and numerical wave hindcasts all show a signiﬁcant increase in winter wave height over the last decades in the northeast Atlantic, north of 50◦N.

"While trend magnitudes showed some variability between the studies, these trends have been shown to be much greater in the last half century than in the whole last century and even beyond.

"In contrast, the change in interannual variability and periodicity of the winter wave activity has received much less attention."

The study combined 69-years of weather and wave hindcast to measure changes in wave height and variability on coastlines from Scotland in the north to Portugal in the south.

These were then correlated against two climate indices - the NAO and the West Europe Pressure Anomaly (WEPA), based on atmospheric pressure along the Atlantic coast of Europe.

The results showed all areas had seen an average rise in winter wave heights during this period, although it varied from 0.39in or 10mm/year in Scotland, to 0.19in 5mm/year in France and 0.04in or 1mm/year in Portugal.

The same scientists have previously shown that the winter storms of 2013/14 were the most energetic to hit the Atlantic coast of western Europe since records began in 1948.

The study which also involved scientists at the University of Bordeaux was published , in Geophysical Research Letters, a journal of the American Geophysical Union.