The extreme winter of 2014-2015


© Tony Butt 2014 - Please be decent enough to contact me before plagiarizing my stuff
 

The real conflict of the beach is not between sea and shore […] but between man and nature. On the beach, nature has achieved a dynamic equilibrium that is alien to man and his static sense of equilibrium. Once a line has been established, whether it be a shoreline or a property line, man unreasonably expects it to stay put. - Gary Soucie


The winter of 2013-2014 can definitely be described as ‘extreme’.  From around the middle of December until the beginning of March the North Atlantic went crazy. A continuous stream of low pressures hurtled across the Atlantic, generating non-stop swell often accompanied by storm-force onshore winds. The winter was exceptional not just because of the level of storminess and the record-breaking wave heights, but also because of the persistence; a run of low pressures usually stops after a couple of weeks but this one lasted nearly three months.

In this article I’m going to run through a few details of the storms, touch on why the waves got so big, and philosophise a little bit on we call ‘coastal destruction’.

It all started on 28th October when an exceptionally large, long-period swell set the scene for what was to be remarkable winter. At one of my local spots in the northwest of Spain I saw the swell pick up from about one foot at three in the afternoon to well over 20 feet by six o’clock. Peak periods were in the region of 17 secs – unusually long for this part of the world. But then the surf went quite small again, and we all thought that the swell of 28th October was a probably one-off. By the end of November I was starting to get worried that we’d only had one big swell, and time was ticking away.

Then, around the first week in December I spotted a change in the charts, with another big swell forecast for Friday 13th. I remember telling everybody that Friday 13th was going to be the day that everything changed. I didn’t know how right I was.

The North Atlantic didn’t stop pumping until about 3rd March, with a constant stream of low pressures, sometimes tracking a little further north and finishing up over Ireland, sometimes a little further south and ending up in the Bay of Biscay, but often slamming into the southwest of England, with storm-force winds accompanied by huge, long-period swells.

There were several storms that stood out, but the one that will certainly go down in history developed around 5th January, the so-called ‘Hercules’ storm.  Even though the central pressure didn’t get as low as others in the past (the Braer Storm of 1993, at 916 mb, still holds the record for the lowest mid-latitude depression ever recorded) the persistence and size of the wind-field around the Hercules storm and the swell it generated were unprecedented for the North Atlantic (Figure 1).

At one point the wave models were forecasting open-ocean significant wave heights of over 20 metres and coastal wave heights of around ten metres with peak periods of over 20 secs. Not knowing what to expect, because this was the first time anybody had ever seen a swell like this, I paddled out at a spot that normally struggles to get big enough to break, and watched it go from virtually nothing to wildly out of control within the space of about two hours, with some sets well into the 30-foot category.

Other events that stand out were the storm of 1st and 2nd February, where one of the highest tides of the year coincided with the peak of the swell. This caused extensive damage to coastal structures and left the coastline seriously eroded. Importantly, the initial erosion swept away a lot of the human structures designed to protect our human settlements (houses, roads and car parks), or flattened a lot of the dunes and natural structures behind which we have built those settlements.  The coastline was then left like an open wound, highly vulnerable for further ‘attacks’ from what a lot of people were now considering our number one enemy: the sea.

Subsequent storms, which included big ones on 5th and 8th February, did cause a lot of further erosion and damage to coastal structures, with the last one occurring on 2nd March. When I wrote this article (mid-March) things had calmed down considerably.


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Figure 1: Classic Met Office isobar chart for the ‘Hercules’ storm of 5th January. In the end we got used to looking at charts like these for most of the winter


Why did the waves get so big?

The height of the waves produced in a storm is dependent upon three factors: the distance over which the wind blows (the fetch), the length of time the wind continues to blow over that fetch (the duration) and the strength of the wind itself.  The strength of the wind is the dominant factor, since its relationship to the wave height is quadratic, rather than linear.  In the storms of 2014, the wind did become very strong at times (well over 50 kts), over large fetches and during extended periods of time, which meant that the waves got bigger than normal; in some cases much bigger (Figure 2).


 
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Figure 2:  Wind charts for 5th January (‘Hercules’ storm), and swell chart 12 hours later.  You can see a huge area of winds of over 50 kts that persisted for at least 24 hours, producing wave heights in excess of 20 metres in the middle of the North Atlantic

 

However, sometimes the waves got much bigger that they normally would have with the same windspeed, fetch and duration, so there must have been some other factor involved. 

There is one other thing that you sometimes find with low pressures on the move: if the windfield is following the very swell it is producing, energy will continue to be pumped into the waves as the windfield moves along.  This has the same effect on the waves as extending the length of the fetch while maintaining the full strength of the wind over that fetch.  It is one reason why western coastlines tend to get bigger and more powerful surf than eastern ones. The storms move towards those coastlines, sometimes at the same velocity as the swell itself, which keeps the windfield synchronous with its own swell and ensures that the waves are continually being pumped with energy. 

Of course, this ‘fetch-swell resonance’ or dynamic fetch doesn’t always happen; low pressures can move erratically and the strongest windfield isn’t necessarily always facing the same direction as the trajectory of the storm.  But it did happen for several of the storms this year, for example on 2nd and 3rd March. For these storms the size and strength of the low pressure itself was unremarkable, but waves over ten metres high were forecast for the Bay of Biscay. The main fetch on the southwest flank of the system, containing very strong winds from the west-northwest, followed a trajectory from west-northwest to east-southeast – approximately the same direction as the swell it was producing, at approximately the same speed (Figure 3).


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Figure 3: Wind and swell charts for 2nd March storm, showing how the windfield and the swell it was producing moved in sync with each other


Why did the water ‘invade’ us?

When the waves reached the coast, why didn’t they stop when they encountered sea walls, promenades, piers and breakwaters?  Even if the waves broke a long way out from the shore, why did the water at the shoreline itself surge over onto parks, walkways, roads, shops and houses? 

Firstly, if high tide happens to coincide with very large waves, the movement of the water due to the waves themselves will be added to the already high level of water, making it much higher every time a wave crest reaches the shore. On 1st February for example, one of the highest high tides of the year coincided with the peak of the swell.

But apart from the simple addition of the waves themselves onto the tide, there are other factors which enhance the height of the water at the shoreline during big storms.

One of these factors is called wave-induced set-up.  This is where the water literally ‘piles up’ on the shoreline due to the action of the breaking waves.  Broken waves (but not unbroken ones of course) carry vast amounts of water towards the shore, on the surface, in the form of lines of whitewater.  This water eventually finds its way back out to sea again in rips and undertows; but first it is pushed up against the shore by the force of the waves, holding it up there and causing the water surface to slope upwards towards the shoreline.  The result of set-up is that the average water level will be pushed up sometimes several metres higher than high-tide level. This is a constant ‘background level’ in addition to the normal up and down motion at the shoreline due to the waves themselves.  Since the set-up is dependent upon the size of the breaking waves, it will be at its largest during big storms.

But perhaps the most important factor – and the most dangerous – is infragravity waves. Infragravity waves are extra long period waves that manage to find their way up estuaries, around headlands and behind breakwaters, actually getting bigger while the ordinary waves are getting smaller. If you didn’t know what these waves were, you might think that they were small tsunamis. They are not technically tsunamis, although they have similar characteristics. The shoreline itself moves in and out hundreds of metres, often flooding over dunes and car parks and into shops and cafes, and then turning around and drawing back out again, sucking all sorts of debris with it. 

Just like tsunamis, infragravity waves are so long that they don’t break, not even on the most gently-sloping shorelines.  Instead, they just surge in and out, sometimes several hundreds of metres, with periods of many tens or even hundreds of seconds.  The result is a further increase in the height of the water at the shoreline, accompanied by a massive surge of water, perhaps not very high, but hundreds of metres thick.  This time though, the surge of water is on a periodic basis, which is even more frightening and unpredictable for the local population.  And of course, the height and wavelength of the infragravity waves will be bigger if the open-ocean height of the waves is bigger.

One really important feature of infragravity waves is that they actually increase in size as they approach the shore.  Because of their exceptionally long wavelength, they never get steep enough to break.  But as they come into shallow water they slow down, which causes them to ‘jack up’ in the same way as ordinary waves do when they hit shallow water.  The wave is squashed up horizontally and pushed up vertically.  In fact, because infragravity waves never break, they keep on growing like this all the way to the shoreline and reach their maximum size at the shoreline itself.

From a surfing point of view, when the waves become so huge and out of control you have find smaller spots to surf – spots facing away from the main swell direction, behind a headland or even a short distance up an estuary. However, these spots can sometimes be more dangerous than those on the open coastline because of the infragravity waves.  Even when the ordinary waves are filtered down to a fraction of their open-coast size, the infragravity waves just keep ploughing on through, actually getting bigger as they pour into the nooks and crannies of tucked-away beaches. The infragravity waves corresponding to a 30-foot swell will still reach that round-the-corner spot even though the ordinary waves might now only be three or four feet high. Even if you think you’ve escaped the gigantic swells, the infragravity waves are still there, lurking underneath, ready to spoil your surf session, or, worse, sweep you out to sea.

A good video of infragravity waves hitting Cornwall, can be seen HERE


Root causes

Trying to find one single ultimate cause for a winter like the one we have just had is probably meaningless, because, like anything to do with Nature, it is due to a particular combination of circumstances involving a huge number of mechanisms. For example, scientists have identified such remote factors as anomalously high rainfall over Indonesia or the direction and strength of biannually-oscillating airstreams in the stratosphere.

Certainly one of the proximate causes of the particularly stormy winter we have had is the behaviour of the upper airstream – the jet stream – over the North Atlantic.  This year the jet stream was up to 30 percent stronger than average, and it flowed across the North Atlantic in almost a straight line from west to east.  When the jet is like this, the extra energy in the upper airstream filters down to the surface and allows deep low pressures to form, steering them into the coasts of Western Europe.

There is also evidence that the low pressures themselves help to maintain a strong jet stream, resulting in a self-perpetuating feedback mechanism between the surface and the upper airstream.  Therefore, once the North Atlantic is locked into a state like this, it tends to stay there for a while. 

This year, instead of reverting to a ‘blocking’ phase, where a large high pressure establishes itself in the middle of the North Atlantic and the jet weakens and develops a large meander around the north of that high, it stayed ‘fluid’ for almost the entire winter. This two-phase behaviour of the North Atlantic is called the North Atlantic Oscillation (NAO).

One thing that also helped the North Atlantic to be more energetic than normal was the above-normal sea surface temperature around latitude 30 degrees north, while temperatures further north were nearer normal. Greater north-south sea-surface temperature differences lead to stronger north-south pressure gradients in the atmosphere which, in turn, mean a greater chance of big storms. Why the temperature was higher is another matter.

And just to dig a little deeper, we can look ‘up-stream’ at the jet over the Northeast Pacific. Here, a huge meander was present, deflecting the jet much further north than usual, and being associated with a large, persistent area of high pressure of the west coast of North America.  In other words, the Northeast Pacific was ‘blocked’ while the North Atlantic was ‘fluid’. The northerly deflection of the jet as it continued over North America means that it picked up a lot of really cold air over Canada, which then contrasted with the warmer air at the entrance to the Atlantic jet. This extra temperature gradient was conducive to a stronger Atlantic jet and more chance for big storms. Again, the reason why there was a large meander in the Pacific jet stream is another matter.

Scientists have gone further and further back, trying to identify more and more obscure causes, but with something like this, you can’t really find a single, ultimate cause. In the end you find that is a unique combination of circumstances that all come together at the same time, each one affecting the others in a maze of feedback loops.

Of course, there is one thing that could be an important contributing factor in all of this, and perhaps something that could tip the balance so that we are likely to have more winters like this in the future: climate change.

Climate change is happening, we all know that. There is now overwhelming evidence that the planet is warming up and the sea level is rising. Apart from a few die-hard sceptics with vested interests in the oil industry, most of us agree that there is more global warming than there should be because of human activities. In fact, the Intergovernmental Panel on Climate Change (IPCC) now state that it is between 95 and 100 per cent certain that human activities are causing global warming. However, to attribute increased storminess to human-induced climate change is a bit more difficult.

Before we even start, we have to make sure that there is actually a systematic increase in storminess over the North Atlantic. We need to make sure that extreme winters such as 2013-2014 aren’t just part of the natural variability of the weather in such a changeable area such as the North Atlantic. According to a recent study by Xiaolan Wang and colleagues, published in the journal Climate Dynamics, the storminess does seem to be increasing. Wang et al looked at data going back to 1871 and found that, in the North Atlantic, the intensity of storms has increased, and the intensity of the strongest ones has increased even more. 

To find out whether human-induced climate change contributed to the systematic increase in storminess in the last 143 years, and whether it contributed to the extreme winter of 2013-2014 needs more research.  Up until now, this research has been hampered by a lack of computing power. Computer technology is advancing fast, so pretty soon we should be able to find out. 

Importantly, if Wang is right and the North Atlantic has been getting stormier over the last century – for whatever reason, global warming or not – we can expect more winters like 2013-2014 in the near future.


Coastal erosion

The sustained wave heights over the winter of 2013-2014 resulted in extreme erosion along the coasts of Ireland, Wales, England, France, Spain, and Portugal, and probably beyond.  Tourist beaches were ‘robbed’ of valuable sand, and coastal urbanizations were destabilized, damaged and destroyed.

During the days following some of the storms, I was able to check the after-effects along some of my local beaches.  In many places I was astounded when I saw how far the sea had reached.  Massive surges of water had snaked their way through gaps in the dunes, across fields and into the woods, and had completely flattened grassy areas and left debris hundreds of metres inland.  The morphology of the beach was completely changed. There was sand were there hadn’t been before, and rocks exposed where sand had been.  

In general, I could see that the coastline had eroded.  Movable material had been displaced from the land to the sea.  But I knew that it hadn’t really ‘hurt’ the coastline itself; the ‘damage’ was not permanent.  It made me think how a simple system of dunes, sandbars, grass and trees is actually far more resilient than some clumsy concrete structure built by humans.  When these events occur, the natural coastline simply moulds and flexes a little, adapting itself to the energy without the slightest hint of tragedy. In contrast, our coastal roads, walkways, shops and houses end up being destroyed by the sea. Concrete structures such as sea walls, piers and breakwaters, that we have invented to protect the hotels, shops and houses that we have built on the coast, don’t seem to be doing their job.  

The reason for this is simple.  It is because, in a natural coastal system, all the components of the system – not only the ‘solid’ ones like the sand and the dunes, but also the energy fluxes like the weather, the storms and the waves – evolved together over thousands or even millions of years, to function in harmony with each other.  A concrete structure designed by engineers with a limited budget and a limited deadline, and whose purpose is to ‘defend’ what we think of our ‘territory’ against what we think of as our ‘enemy’ (the sea) is doomed to fail because it did not evolve in the same way. 

 

Reanimation of marine litter

Human litter accumulates on the coastline, either brought in from the sea or dropped by people on the beaches. When the beach is in an eroded state, during any normal winter, this rubbish still finds its way onto the beach; but it then gets buried during subsequent periods of coastal accretion, typically in summer, when the sediments build up again. Over time, some of this rubbish gets buried deeper and deeper into the sediment, becoming encrusted like layers of sedimentary rock.

The massive amount of erosion produced by the storms this winter has suddenly uncovered a vast amount of rubbish, in some cases dating back decades. Beachcombing has become more like archaeology, with people finding crisp packets, drinks containers and other consumer packaging from the 1970s, still in perfect condition. With all this litter now on the surface, the coast has become a much more toxic place to be. And of course the rubbish is free to move around get washed into coastal waters, causing further contamination.

Just seeing all that stuff having been suddenly uncovered ought to shock people into realizing what a huge problem marine litter is, even if they didn’t think it was before. Mostly consisting of plastics, it just doesn’t go away. Layer upon layer have been covered up by sedimentary accretion over the years, literally swept under the carpet. But now the carpet has been lifted and we are suddenly overwhelmed with thousands of tonnes of rubbish. Hopefully it will at least make people understand the enormity of the problem, and be more willing to support groups who are working hard to try to solve it.

 

Rainfall and coastal pollution

The extreme winter of 2013-2014 brought coastal flooding due to the huge waves, as I explained earlier. But it also brought flooding due to the immense amount of precipitation that the storms carried as they made landfall. The rain was not evenly-distributed light drizzle; it was more like highly intense, heavy downpours.  In these situations, the inability of drainage systems to cope with a sudden massive input tends to lead to increased pollution of coastal waters.

When it rains ‘too much’, polluted water starts to find its way into the sea in two ways: overflow from sewerage systems that cannot cope with the increased volume, and the running off of surface water from the land into the sea, dragging nasty chemicals with it.  In urban areas, rainwater from people’s roofs and from drains in the road often gets channelled into the same sewers that our toilets and sinks are connected to.  If the rainfall suddenly increases, then all that extra water might not fit into the sewers.  When this happens, the excess rainwater and raw sewage, all mixed up, are directed straight into the sea. 

Excess water running off the land also will pick up a lot of residues on its way to the sea.  These might include pesticides and animal faeces from farmlands, oil and dirt from roads, poisonous chemicals from industrial areas, and every imaginable nasty from landfill rubbish dumps.

 

To conclude, the ‘extreme’ winter of 2013-2014, and the consequential destruction of human coastal structures, should be thought of as a big wake-up call. If people still think that they can own and control a narrow strip of land that has evolved over millions of years to absorb the energy of the sea, should think again.

The fact that our coastal edifications get damaged during storms is nobody’s fault but our own. And this is true even if the storms are totally natural, and we are not exacerbating them through climate change.  Our roads, houses and car parks get washed away simply because we put them there.  Building something too close to the coast, in other words building something in a place which gets inundated by the sea on a periodic basis, is just plain daft. It is like building a sandcastle at low tide and then building a wall (made of sand) around it to stop it getting washed away when the tide comes in.  

And, if we are actually contributing the increased storminess because of climate change, that’s even worse.

So, what’s the solution?  I don’t have the definitive answer, but I believe that a change of attitude would help a great deal.  At the moment we think that when a storm comes the sea is trying to advance into ‘our’ territory; so we put down ‘territorial markers’ in the form of concrete structures designed to stop the ‘enemy’s advance.  That is obviously all wrong. The sea is not our enemy; it is part of Nature, just like we are

Instead of believing that we are somehow separate from the other elements that make up the planet, and somehow superior to them, we need to realize that we are a just another part of Nature, just like the sea, the rocks, the plants, the fish, the dunes and the weather.  If we insist on trying to fight with Nature, we are, in a way, fighting with ourselves.