Extreme wave events in Ireland: 2012 - 2016

. This paper aims to extend and update the survey of extreme wave events in Ireland that was previously carried out by O’Brien et al. (2013). The original catalogue highlighted the frequency of such events dating back as far as the turn of the last ice age through to 2012. Ireland’s marine territory extends far beyond its coastline and is one of the largest seabed territories in Europe. It is therefore not surprising that extreme waves have continued to occur regularly since 2012, particularly considering the severity of weather during the winters of 2013-14 and 2015-16. In addition, a large number of storm surges 5 have been identiﬁed since the publication of the original catalogue. This paper updates the O’Brien et al. (2013) catalogue to include events up to the end of 2016. Storm surges are included as a new category and events are categorised into long waves (tsunamis and storm surges) and short waves (storm and rogue waves). New results prior to 2012 are also included and some of the events previously documented are reclassiﬁed. Important questions regarding public safety, services and the inﬂuence of climate change are also highlighted. 10


Introduction
The study of extreme wave events in the ocean has become a popular area of research in recent years. Aside from sea-farers, extreme waves impact coastal communities and are of great interest to wave energy companies. This is particularly prevalent in the face of coastal erosion, rising sea levels and uncertainty in how the wave climate will change in a warming world. However, much of the current research is based on modelling and experiments. Aside from Kharif and Pelinovsky (2003); Tinti et al. 15 (2004); Nikolkina andDidenkulova (2011) andO'Brien et al. (2013), there are few studies documenting the observations of such events.
The purpose of this paper is to extend and update the the work of O' Brien et al. (2013), a catalogue of extreme waves around the island of Ireland. Ireland's marine territory extends far out into the Atlantic and covers approximately 880, 000 km 2 . O' Brien et al. (2013) documented extreme wave events extending as far back as 14 680 BP through to 2012, including 20 storm waves, rogue waves and tsunamis. Since its publication, an Irish Costal Protection Strategy Study (The OPW and RPS, 2013) has highlighted the huge number of storm surges that have occurred in Ireland. We therefore incorporate storm surges as an additional category in this paper. We also distinguish between two wave groups, long and short, since their characteristics are distinct. Our study includes new events that have been identified prior to 2012, recategorises events from the previous catalogue (O'Brien et al., 2013) and extends this catalogue out to 2016.
The paper is organised as follows: Section 2 gives an overview of the categories of ocean waves included in this study, Section 3 revisits the events from O' Brien et al. (2013). New events identified prior to 2012 are outlined in Section 4, and a catalogue of events from 2012 to 2016 is laid out in Section 5. A wider selection of issues relating to extreme waves are 5 discussed in Sections 6-9: these are boulder deposits, climate change, public awareness and services, respectively.

Categories of ocean waves
In O' Brien et al. (2013) waves were broken into three categories: storm waves, rogue waves and tsunamis. Storm surges and meteo-tsunamis were included as a subsection of tsunamis as they are both long-period waves with a meteorological origin.
Since this publication, new data (The OPW and RPS, 2013) highlighted a huge number of storm surge events between 1961 10 and 2005. With this in mind, upon review of the events documented in O' Brien et al. (2013), some have been recategorised as storm surge events. In this paper, we give storm surges its own category due to the large quantity of events that have come to light.
In addition, we feel it is appropriate to divide the wave categories into two streams: long waves and short waves. Generally, the ratio of depth to wavelength is used as a parameter to differentiate between long and short waves. Long waves can be 15 modelled using a simplified set of equations, called the shallow water equations. Tsunamis and storm surges are typically very long waves, so they are considered shallow water waves. Storm waves and rogue waves are much shorter in wavelength relative to the ocean depth. The dimensionless wave number is kh where k = 2π/λ, λ is the wavelength, and h is the water depth. Tsunamis and storm surges have kh values of the order 10 −3 − 10 −1 , while for storm waves and rogue waves kh values are of the order 1 − 10 3 . Typical values for wavelength (λ), water depth (h), and period (T ) for storm waves, rogue waves and 20 tsunamis are given in Table 1. The dispersion relation for short waves (ω = √ gk) and for longer waves (ω = gk tanh(kh)) is used to calculate the range of periods, T in this table. For long waves we calculate the period based only on the upper limit of λ.   Bricker (2015) replicated this event showing that it was mainly due to the abrupt breaking of energetic storm waves over the steep reef face rather than a storm surge. Table 1 can be used as a guide, however there are always going to be events that are exceptions to the rule. For example, although kh is generally large for short waves, a rogue wave was measured by a Waverider buoy at Killard (Figure 11) in 39 m depth with a corresponding kh = 0.74.
2.1 Short waves 5 2.1.1 Storm waves Storm waves are wind surface waves that reach unusually large amplitude due to forcing by strong winds. For example, storm to hurricane force winds ranging from 10 to 12 on the Beaufort scale have probable maximum wave heights from 12.5 m to 16 m and beyond (The Met Office).
The prevailing wind direction in Ireland is from the south and the west, and on average there can be more than 50 days with In addition, waves approaching a cliff can be significantly amplified by a variable coastal bathymetry. Herterich and Dias (2017) have shown that the waves could be amplified nearly 12 times around the Aran Islands (3 islands off Co. Galway, on the west coast of Ireland).
With strong winds so prevalent in Ireland and coastal bathymetries potentially favouring significant wave amplification, 20 storm waves are an important category of extreme ocean events in this catalogue.

Rogue waves
Rogue waves are large-amplitude waves surprisingly appearing on the sea surface (Kharif and Pelinovsky, 2003). They seem to appear from nowhere with a height 2 − 3 times that of the surrounding sea state, exist for a short time and then disappear.
The mathematical criteria 25 H/H s > 2 and/or η c /H s > 1. 25 where H is the (trough-to-crest) wave height, η c is the crest height and H s is the significant wave height, are commonly used (Dysthe et al., 2008). Rogue waves are also referred to as freak waves, monster waves or king waves. Once thought to be folklore of seafarers, they are now accepted as an important class of wave. This is due to recent scientific investigations motivated by account of huge waves hitting ships (Kharif and Pelinovsky, 2003;Didenkulova et al., 2006) and measurements of 30 unusually large waves from oil-platforms (Olagnon and Prevosto, 2004;Magnusson and Donelan, 2013; Christou and Ewans, 2014; Fedele et al., 2016;Cavaleri et al., 2016;Donelan and Magnusson, 2017). Rogue waves are random in nature, occur in both deep and shallow waters, and may act as a single wave or a group of waves. It is almost certainly the case that different mechanisms can contribute to the formation of rogue waves, including both linear and nonlinear processes influencing waves both in the local vicinity of a wind sea, as well as propagating swell. For example, linear superposition and directional focussing effects could readily increase local wave height in the presence of local wind, whilst nonlinear instabilities could increase local 5 wave group amplitude for a propagating swell.
Work using analogies between ocean deep water waves and light propagation has indeed been able to confirm many predictions (Peregrine, 1983) of nonlinear deep water wave growth and decay in an optical environment (Kibler et al., 2010(Kibler et al., , 2012. However, Fedele et al. (2016) recently investigated real world ocean rogue waves and showed that their observed results could be explained by directional focussing. A discussion of linear and nonlinear rogue wave mechanisms is given in Dudley et al. 10 (2013). Draper (1971) discusses the expected frequency of large waves in the context of the statistical distribution of the maxima of a random function theory by Cartwright and Longuet-Higgins (1956). In particular, he points out that the theory indicates we should expect one in 1175 waves to exceed three times the average wave height (∼ 1.9H s ) and one in 300,000 waves to exceed four times the average wave height (∼ 2.5H s ). 15 Note that field measurements of maximum wave heights (H) in constant depth generally do not exceed 0.55h (where h is water depth) and tend to break before reaching this height (Nelson, 1994;Babanin et al., 2001 10 It is common that the first sign of a tsunami is an extreme withdrawal of the sea followed by a wave that seems small in the distance, but which grows rapidly and which can be followed by successive waves sometime after. The first wave is not always the largest (Stefanakis et al., 2011;Okal and Synolakis, 2016). Without the proper infrastructure and education of the warning signs and evacuation methods, tsunamis can have deadly effects on coastal communities.
Small tsunamis can also occur. They appear as disturbances with the same generation mechanisms and characteristics of a 15 tsunami without being life threatening. There are cases in harbours where the tide has unexpectedly risen and fallen repeatedly every few minutes over the course of an hour or two. For example, in Rabaul, Papua New Guinea a small tsunami occurred on the 29 March 2015, "residents noticed the sea level rose slightly, prompting ocean water to flood the parking lot of a shopping center near the beach" (National Oceanic and Atmospheric Administration, 2016).
Meteo-tsunamis are waves with tsunami like characteristics but are caused by air pressure disturbances often associated with 20 fast moving air such as squall lines. Their development depends on the characteristics of the disturbance (speed, intensity, direction) and they can be magnified by resonances associated with the depth of the water or when travelling in semi-enclosed water bodies (National Tsunami Hazard Mitigation Program, 2015). Although there are not many documented incidents of meteo-tsunamis relative to regular tsunamis, and even less of meteo-tsunamis that have become dangerous, a 2 m wave in 2013 injured three people in New Jersey and a 5 m wave killed three people in Nagasaki Bay, Japan in 1979 (Kathleen Bailey and 25 Welty, 2014).
If there is no known origin of a tsunami like wave it can be difficult to differentiate between a small tsunami and a meteotsunami. For example, underwater landslides can occur without notice other than the generation of a wave, so it is important to consider different generation mechanisms in each case.

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A storm surge is an unexpected rise in sea water level generated by a storm. The low-pressure area near the storm's eye reduces the weight of the air over the ocean. This creates a swell in the sea which is pushed towards the coast by the strong winds. As the storm approaches the coast, the combined effect of the low pressure and the violent winds makes the water pile up along the shore. It is a long-period wave and can have particularly destructive effects in coastal areas where there is a significant difference between low tide and high tide.
In Europe, storm surges alone usually do not generate coastal flooding. Coastal flooding occurs when a storm surge hits the shore together with high tides. To the coastal communities, the effect of the surge-tide coupling is the same as a small tsunami, 5 despite the physics being very different.
The climate in Ireland is dominated by the Atlantic Ocean, in particular the structure of the polar front over the Atlantic and the associated weather systems that travel across Ireland. These systems can often amplify and become large scale depressions that move north eastwards across the North Atlantic and pass to the northwest of Ireland (Met Éireann, 2016b). Sometimes this can lead to storms travelling across the ocean that initiate storm surges and lead to coastal flooding. 10 The period of storm surges can range from 2.5 hours to a day and excludes wind waves and choppy sea, since they are characterized by periods smaller than a minute. The only formal difference between a storm surge and a meteo-tsunami consists in the difference between their maximum periods. The maximum period for a tsunami does not exceed several hours, while storm surges may last up to a day. The 29 December 1894 event has been upgraded to a storm surge due to the eye witness description of a terrible gale that was blowing all night, with "Green seas... going over our houses", and all the rooms "filled with the sea" (Ryan, 1895  This event in January 1877 was most likely a storm surge going by the description of flooding on the train line, "The train

1941 Inisheer Lighthouse, Aran Islands, Galway Bay [S7]
The reference to severe flooding at Inisheer lighthouse in January 1941 suggests that this event was a storm surge (Williams and Hall, 2004). On the 18 December 1945 gales and high tides hit many coastal towns. The description of an "exceptionally high tide" that washed away part of the cliffs in Rosslare bay indicates that this event was likely to have been a storm surge (The Irish Times 19 December 1945).

1953 Aran Islands and Irish Sea [S10]
20 During a storm in 1953 a large number of megaclasts at Gort Na gCapall on the Aran Islands were shifted (Williams and Hall, 2004) indicating that it was likely a storm surge had occurred.    September 1841 (Milne, 1844). "the attention of the inhabitants was attracted about noontime, to a number of short, loud, but rather smothered reports, like cannons, and it was supposed that they proceeded from some ship bewildered by the fog. The 5 tide had flown pretty well at the time, and the fishing boats in the pier were all afloat, when, in a space of two or three minutes, the water receded from the pier, and some walked dryshod where the short pace before the boats had been floating in five or six feet of water. In the course of a few minutes the waters began to return, much in the same way as they had receded, and the tide continued to rise for the usual time. There was no extraordinary commotion, only an increased surf. After repeated rolls in thunder, and some heavy showers, the sky cleared up. It is the belief generally that this singular motion was the effect 10 of an earthquake, whose shocks have of late been so frequently experienced in Scotland." The recession and return of the tide in such a short period of time would suggest that this was definitely a tsunami, but it is not clear what caused it. The weather preceding the wave is described as "a misty dark day, with the wind SSW to S... the low growel (sic) of distant thunder was heard, and the wind lulled, which rendered the fog more dense". This might suggest a meteorological origin, however this is only speculation.   The description of this event indicates that more likely it was a storm surge, not a meteo-tsunami. In particular the "Violent Gales" and tide rising to a height "not seen for very many years" would correspond to a storm surge. immediately battled gales attempting to head south for many days without making much headway. On the morning of the 24 December the captain, with an exhausted crew, decided to make a run for Dublin Port. However, as the visibility worsened and they battled constant rain squalls they headed for Kingstown Harbour but were unable to navigate to safety so let their anchors go outside the West Pier. Two lifeboats were sent to rescue the crew and as the first approached the ship it was hit by a huge wave and capsized. The ship's crew attempted to launch one of their boats to rescue the men but it was smashed against the 10 ship's side in heavy seas. The second lifeboat also capsized twice and lost half her oars but righted and the crew managed to get to safety at Blackrock. Thirteen of the crew's bodies were washed up on Christmas day and the other two several days later. They included a father and son, two pairs of brothers and left a total of thirty-four children fatherless. Astonishingly, all nineteen people aboard the ship were saved when the weather abated on the 26 December. (Louth, 2013).
There is a memorial to the crew at Dun Laoghaire shown in Figure 5.

1903 Storms across Ireland
The period ending February 1903 was very stormy with depressions from the Atlantic bringing very unsettled weather across Ireland. The night of 26th to 27th was probably the most severe storm since "The Night of the Big Wind" (Met Éireann, 2016a).
On the 26th, the Lady Disdain, a 25 ft yacht was wrecked in Valentia harbour, Co. Kerry, on its journey from Kingstown (Dun Laoghaire) to Nenagh. Thursday last "there burst on the bay the hurricane which swept the whole of Ireland". At about 4pm "the great wind came on" and "Great waves rode down the harbour tossing the biggest vessels like cockieshells". It was driven ashore and struck rocks. (The Irish Times, 5 March 1903) Also associated with this bad stretch of weather was the drowning of a 9 year old boy at Portrush, Co. Antrim, while he was on a patch of strand beneath the promenade. It was windy and the waves "frequently at long intervals" swept over the rocks and sand. The boys cap blew off and when he went to get it a "tremendous

1935 Arranmore boat disaster
On 9 November 1935, a small boat carrying 20 people from Burtonport harbour, Co. Donegal to Arranmore Island hit rocks and sank. There was only one survivor and among the casualties were 12 people under 30 years of age, and 7 from the same 15 family. Many were returning from Scotland after picking potatoes for the season. Although the accident reportedly occurred in a heavy swell, the cause was due to the boat hitting rocks. It is therefore unlikely that this can be attributed to a wave. However, the stretch of sea is known for being treacherous, and 15 people died in three other incidents over the same area. (The Irish Times, 11 November 1935, andRTÉ (2016c)

1998 Extreme storms
Severe weather hit Ireland and Europe on the 4th January 1998, causing major disruption to ferry and airline services, and the rescue of 10 fishermen from their sinking trawler 190 miles south of Castletownbere, Co. Cork. They were under tow after their engine failed and when the tow rope broke and they were "at the mercy of the huge seas" in "force 11 gales" (103 − 117   (1971) : 1967-2006, SE and NE: 1959-2005, SW, NW and W: 1959).
Inland areas can also be affected by storm surges, for instance if an area is connected to the ocean by an estuary or river.
Therefore, some inland flooding events have been included as coastal flooding events in this paper. These are restricted to events within ∼ 10 km of the coast. It is also important to note that there are many storm surge events that have reports of 5 major coastal flooding associated with them, however no inundation depths are reported, this is particularly true in earlier years. Therefore, there may be storm surge events that caused coastal flooding in excess of 0.5 m that are not included in this catalogue due to a lack of available information.
Between 1961 -2006 we identified 40 periods where coastal flooding was generated in Ireland, this is nearly an average of one per year. It is interesting to note that all but 2 of the periods occurred between late autumn (October) and early spring 10 (March). The inundation levels associated with the storm systems of Table 3 vary from the threshold level of 0.5 m to a couple of metres. Sources were scored according to their reliability, from 'A' to 'C'. A level 'A' source is an official technical report, level 'B' indicates a report in a newspaper article, while a level 'C' source is an eyewitness account in a newspaper article.

1942 Co. Kerry
A severe storm swept over Co. Kerry during the week of the 12 December 1942 with the "Highest Seas since 1928". Many 15 boats were destroyed and the storm was described as what may be "the worst ever experienced", with flooding and the seawalls were "completely demolished", "badly breached" or "washed way". One house was flooded with sea water 0.6 m (2 ft) deep.
A well known landmark, a large rock, disappeared. The lighthouse lamp was put out by huge seas and high winds. Large quantities of seaweed were strewn across the streets and the beaches were covered with fish. Damage to fishing boats and nets were caused by "mountainous seas and very high tides".

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It was believed that sheep were blown off the cliffs in one area, while it was reported that a "tidal wave" washed seven cattle and sixty sheep off an island near the Derrynane coast. There was a narrow escape by a 73 year old man who swam to safety in Kenmare Bay when his boat was swept from her mooring and smashed into pieces. Unfortunately his little dog was found with the wreckage the following day. (The Kerryman 19 December 1942) The description of high tides and tidal wave suggests that this event was a storm surge.    10 The ICPSS (The OPW and RPS, 2013) don't include this event in their reports, however there was clearly significant coastal flooding associated with it. Therefore, flooding in excess of 0.5 m is shown in Table 4 in the same style to Table 3.

1974 Storms
The weather in January 1974 was mild, wet and stormy as the North Atlantic and a large section of Northwest Europe was under a "sway of complex low pressure area". An extreme storm during the 11-12 January caused extensive damage. In particular full 15 moon spring tides combined with wind and low pressure caused damage to low lying coastal farms and houses. "Roads were blocked by seaweed, rocks or other debris and in some sections destroyed". Many small boats sank and larger boats were torn from their moorings. At Inisboffin, off Donegal, waves were sweeping through the centre cutting it in two temporarily. Also, The descriptions given here imply that this event was a storm surge.

1976 Storm
A storm on 2nd January 1976 caused widespread damage in Ireland. A depression intensified considerably off the north coast 5 of Ireland taking people by surprise and generating storm force winds in many areas. At Limerick, the tide was just 7.6 cm short of its record level (68.6 cm). The coastal town of Ballina, Co. Mayo reported flooding, though it is not clear if this was coastal flooding or due to the river bursting its banks. The sea at Kinvara, Co. Galway "cascaded across the quays" and the tides "swept over the road in two places" nearly cutting off the town. (Met Éireann, 2016a).
The high tides and coastal flooding clearly suggest this was a storm surge event. was washed away". In addition, part of a car park in Cahore, a beach access road at Ardamine and a walking trail in Courtown Woods were washed away. One local described "a high tide, and the wind in the right direction with a big swell", creating the very damaging conditions. (The Wexford People 14 January 2014)

2014 West Co. Cork
Two men died while out walking along the coastline in west Cork. Apparently the two men "had hoped to take photos of stormy seas striking rocks" by a local lighthouse. The route known locally as 'Poet's Path' is very exposed in parts, to the wind 5 and sea. Gardaí (Irish police) assumed that freak waves and gusts of up to 130km/hr caused them to get into difficulty. (Irish Independent, 11 February 2014).

2014 Belderrig, Co. Mayo
The front of a stone built boathouse was destroyed at Belderrig near Belmullet, Co. Mayo, after a large wave hit it on the 10 December 2014. The boathouse sits approximately 10 m above sea level. Nearby, at about 15 m above sea level, a sizeable 10 boulder was found overturned, and about 1 km from the boathouse, at approximately 30 m above sea level, large rocks (∼ 40 − 50 kg) were also found strewn about. One of the locals noticed that the sea withdrew dramatically after one of the large waves hit the coast.
Nearby at Portacloy, the sea state caused a World War 2 look out post to collapse on the same day. A photo of the sea condition in the area on this day are shown in Figure 8. 15 The M4 buoy located off the coast, Northeast of Belderrig, recorded a maximum wave height of 21.5 m on the same day, with a corresponding significant wave height of 14.5 m (see Figure 9). This is not classified as a rogue wave, however the waves hitting the coast of Co. Mayo on this day did significant damage. A local man pointed out that if the large waves had hit the coast at high tide, the damage could have been far worse. (Personal contact with Seamus Caulfield and Gretta Byrne)

2015 Hook Head, Co.Wexford
A 14 year old girl died after she and three other teenagers were swept into the sea off Hook Head, Co. Wexford during a heavy swell in the aftermath of Storm Desmond on the 6th December 2015. The four were part of a scouts group expedition. It was reported that they were walking on the rocks along the foreshore when a "rogue wave" dragged them out to sea. (The Irish Times, 7, 10 December, 2015). The sand dunes at Culleton's Gap (The Raven), near Curracloe, Co. Wexford were altered after gales on the 20th August 2016 1 . Trees that line the beach were damaged, sand was shifted and tree roots were exposed (see Figure 10). Locals say that this  is a common phenomenon in the region, particularly with strong easterly winds. Presumably it is a combination of wind and waves that alters the dunes here. as identified by its crest-to-trough is highlighted in red. A number of large waves with amplitudes close to 20m were recorded on the 22nd February, see Figure 13. This shows that 10 large waves of interest are not always classified as rogue waves.

2015 ADCP Measurements
Note that the ADCP is deployed in an area with water depth h = 36.5 m, therefore we would expect that waves here would not exceed heights of H = 0.55h = 20 m.

2015 The Wormhole, south of Dún Aonghasa, Inis Mór, Aran Islands
On the 8th of April 2015 a student was swept off a cliff face and into the sea by a giant wave at the renowned Wormhole (a

2015 Baltimore, Co. Cork
On the 30th June 2015 four people were hit by a rogue wave while fishing near the Beacon in Baltimore, only one survived.
They were initially hit by a couple of waves and then a "big wave" dragged two of the group out to sea. The other two were pushed up against the rocks, one then jumped into the sea in an attempt to rescue the others but sadly all three drowned. (The Irish Times 26 April 2016). 5

2016 Ballyrean, Co. Clare
A woman drowned after being swept out to sea by a "rogue wave" while fishing with friends in Ballyrean, south of Fanore, Co.
Clare on 10th July 2016. Conditions at the time were harsh with winds reaching gale force 6-7. (Independent.ie 10 July 2016, The Irish Times 10 July 2016). wave buoy, a 30.96m wave was recorded with a significant wave height of 8.8 m, classifying it as a rogue wave. See Figure 14.

2016 Storm Jake
However, the buoys can only be considered reliable within a certain range of displacement from mean sea level, so very large wave recordings like this should be treated with caution. Although, the nearby Belmullet Berth A wave buoy also recorded a very large wave at around the same time ( Figure 14) giving more confidence in the recording.

Storm Surges
The winter of 2013-2014 was severely affected by a large number of storms due to the atmospheric jet stream extending right over Ireland carrying successive storms. This exceptional weather combined with high tides resulted in serious coastal damage and widespread flooding (Met Éireann, 2016a).
In particular, high spring tides on the 3rd January and 1st February coincided with storms on the 2nd -3rd January, 5th-6th 5 January and 1st February causing extensive storm surges and damage around the country. These events are described in more detail below.

2014, January Storms
Storms at the end of December caused some coastal flooding in Cork, Wicklow and Dublin (Irish Independent 2 January 2014) but the storms on the 2nd -3rd and 5th -6th January 2014 had far greater consequences. Tide gauges at Rossaveal, Co. Galway  The storm on the 5th -6th January exasperated damage, particularly along the Galway coast with "chunks of coastline"

Buoy Network
The Irish Marine Institute manage a group of offshore buoys deployed around the Irish coast that monitor weather and oceanographic conditions in real-time. Figure 18 shows the distribution of rogue wave and large waves (> 10 m) recorded for buoys M2 -M5 during the period for which data is available for each buoy between March 2011 and June 2016. Notice that waves classified as rogue waves are not often very large. Also, there is a much greater number of large (non-rogue) waves than rogue 5 waves, indicating that more often than not a very large wave is not classified as a rogue wave. buoys don't record many of either wave type, these buoys are located off the East coast and Southeast coast of Ireland in more 10 sheltered waters.  Evidence of boulder deposits due to waves can be found in numerous areas around Ireland (Hansom and Hall, 2009;Williams, 2010;Cox et al., 2010). A review of possible mechanisms for this type of boulder movements is given in O' Brien et al. (2013), though there is no consensus in determining the size of waves at the coast and the masses they can carry. Boulder deposits can be used as indicators of the impact and sheer force of the ocean. However, there is a lack of data quantifying the effects. In Below we list some more recent reports of boulder deposits due to extreme waves in Ireland.

1991 Clifden, Co. Galway
Renvyle House hotel in Clifden suffered severe damage from a storm in early January 1991. It was reported that wave and

Climate Change
Global warming will lead to a rise in mean surface temperatures of between 0.18 • C and 4.8 • C by the late 21st century (IPCC, 2013). This will result in changes to global circulations, particularly the atmospheric jet stream, which is a major driver of Although climate models mostly agree on a poleward shift of the jet stream in response to anthropogenic forcing, there is still considerable spread between different model projections (Woollings and Blackburn, 2012) and uncertainty in how this will affect weather. In particular, there is low confidence in projecting changes in the Northern Hemisphere winter storm tracks, especially in the North Atlantic Basin (IPCC, 2013;Gallagher et al., 2016).
Ireland is strongly influenced by the position of the jet stream as it generally coincides with the path that storms will take 5 as they pass over or near Ireland. Various studies have downscaled climate projections over the 21st century to determine how Ireland's climate is expected to change, the results of these studies are combined in Gleeson et al. (2013).
Some of the expected changes that could influence extreme wave events in Ireland are outlined below: -Increase of cold continental air outbreaks during winter.

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-Increase in frequency of heavy rain events in winter (up to 20%).
-Increase in energy content of the wind (up to 8%).
-A small decrease in mean wave heights, while in winter and spring, storm wave heights are likely to increase in the north and northwest.
These results indicate that, in general, the severity of winter weather is expected to increase indicating that extreme wave 15 events may increase.
However, actual wave climate projections for Ireland have been carried out by Gallagher et al. (2016). This is the first study of its kind providing the highest resolution wave projection data set available for Ireland. They found that 10 m wind speeds over the North Atlantic Ocean (5 − 75 • N, 0 − 80 • W) are expected to decrease by the end of the century (in means up to 3% and extremes up to 14%). They also predict an overall decrease in mean and extreme (up to 15%) annual, winter and summer 20 significant wave heights around Ireland. These results indicate that extreme wave events are expected to decrease in the future.
This seems at odds with the prediction that the winter weather is expected to be more severe. However, it should be noted that the results from Gleeson et al. (2013) are based on mid-century outcomes, while the Gallagher et al. (2016) study uses a different forcing that represents the end of the century.
Further work is required increase confidence in these results since uncertainty remains in the future position of the jet 25 stream, in particular in the North Atlantic (IPCC, 2013;Gallagher et al., 2016), and subsequently the projected changes in wave heights. Additionally, recent research suggests that the effect of the North Atlantic Oscillation (NAO) should be taken into account when considering future extremes, as a positive phase may in fact enhance extremes of significant wave height (Gleeson et al., 2017).

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Ireland has approximately 6000 km of coastline. The Winter storms of 2013-2014 caused huge damage and erosion along this coastline. It is still unclear whether these storms can be attributed to climate change, but Murphy (2014) found that wave conditions that are only expected to occur once a year were exceeded 7 times in just one month during this time. Murphy (2014) warns that if severe storms like these become more frequent, Ireland will need to come up with a strategy for coastal erosion. Further, a predicted sea level rise of approximately 0.5 m is used for most engineering design in Ireland. However, wave setup on exposed coastlines and storm surges (low pressure and onshore winds) can significantly increase water levels.
Murphy (2014) argues that quantifying wave setup and storm surges would be better parameters to apply to engineering design 5 along the Irish coastline.
In addition, Carbone et al. (2013) have studied wave impact on vertical cliffs and shown that certain wave groups may produce higher run ups than previously predicted (exceeding the initial wave amplitude by a factor of 5 showed that run up can be amplified nearly twelve times under certain conditions. These studies suggest that the design wave heights used by engineers for coastal structures may be too low. Tsunami surges result in coastal erosion, while tsunami-induced currents also present an obvious hazard to maritime activities and ports. An event like the 1755 Lisbon tsunami, which generated 2 m waves in Kinsale, nowadays would cause much damage because of the larger number of boats and also pose a danger to human life. There is also the threat of major landslides 15 off the west coast of Ireland (Salmanidou et al., in press) that could not only generate 4 to 5 m waves in Belmullet but also generate complex motions in the surrounding bays. While erosion can change the coastal landscape, so can accretion. More recently, thousands of tons of sand were deposited by unusual tides at Doonagh, Achill Island recreating the strand they had lost to storms 33 years prior (The Irish Times 1 May 2017).
8 Public Awareness and Education 20

Storm Waves and Rogue Waves
Most of the Irish coastline enjoys a seascape free from barriers or restrictions. This is one of the reasons that locals and foreigners alike are attracted to coastal amenities and stunning scenery. However, as evidenced from this catalogue there are dangers associated with extreme waves when venturing so close to the ocean. In particular, there are areas that seem to be accident prone. Between Doonbeg and Kilkee, Co. Clare, 7 rogue or storm waves have caused accidents, while 5 such 25 waves have been documented between Doolin and Fanore, Co. Clare. These sites may be more accident prone due to a higher frequency of extreme waves or, larger volumes of people doing coastal activities in the region. However, given that there have been multiple incidents where people have slipped and fallen into the sea in these areas, it is likely due to the volume of people.
Local knowledge may play a part in these incidents since there are many occurrences involving non-natives. It seems sensible that signs should be present along certain parts of the coastline alerting people to the dangers of extreme waves. Signs do exist, 30 for example see Figure ??, however it may be more effective to emulate road signs identifying a "blackspot" region or, state the number of people who have died on Ireland's coastline. Warning signs should be combined with public education on the Excuse" aimed at people visiting Irish coastal areas over the summer holidays. Figure 19. Warning sign at Kilkee, Co. Clare.

Storm Surges and Tsunamis
Storm surges and coastal flooding are somewhat predictable with modern day weather and tide forecasts. Warnings will often be circulated by news and emergency services prior to a coastal flooding event. When flooding is expected in a region, safety 5 measures are usually implemented by local county councils including the use of sandbags or advising vulnerable people to move to a safe place. The Office of Public Works also maintains a website to inform the public how to prepare for a flood and what to do during and after a flood 3 . However, the lead time, severity and location of flood forecasts could be improved.
Funding for a new flood forecasting unit was announced by the Irish government in early 2016 and is due to be set up by Met Éireann and the Office of Public Works in 2017. 10 When it comes to tsunami forecasting, the International Tsunami Information Center provides warnings from the major tsunami warning centres around the world. So, if a tsunami were heading towards Ireland it is likely that a warning would be circulated. However, knowing that a tsunami is coming is not enough to avoid loss of life. Countries prone to tsunamis have pre-prepared risk maps and evacuation plans for different tsunami scenarios. This does not exist in Ireland due to the low risk of a life threatening tsunami occurring. However, there are two potential sources of large tsunamis that could effect Ireland. 15 The first is a volcano landslide in the Canary Islands and the second, a large underwater landslide off the continental shelf in morning in 1997 at the Forty Foot, a famous swimming area in Sandycove, Co. Dublin, conditions were particularly bad and many of the enthusiastic, but non-regular swimmers got into trouble. One boy was swept away by a "sudden freak wave" and a teenage girl was "bounced at great speed from rock to wall to rock". (The Irish Times, 31 December 1997). Public education would encourage people to be safety conscious and make sensible decisions about whether to partake or not.

25
Multiple organisations manage different aspects of the Irish coastline and marine sectors, some oversee safety while others manage data collection.

Data Services
The Office of Public Works (OPW) is a service organisation in Ireland, one of their main areas of responsibility is flood risk management. They provide real time sea level data recorded at 11 tide gauges on their hydrometric network, including data up to 5 weeks prior, through a web portal 4 . The OPW also maintain a website 5 that contains reports and information about floods that have occurred around Ireland.
The Marine Institute is the agency responsible for marine research, technology development and innovation in Ireland 6 .
It provides access to realtime and past data from twenty tide level stations deployed around the Irish coast, along with 4 wave buoys and 5 weather buoys that are located in various locations offshore. They also provide a 6 day marine forecast for 5 significant wave height, mean wave period and mean wave direction.
The Commissioners of Irish Lights (CIL) manages the Ireland's network of lighthouses, providing a safety and support service around the coast of Ireland. With advances of e-navigation the CIL now has a heavy focus on technology and data services. Real time wave and weather data can be retrieved for seven buoys located at various locations offshore and weather data at two lighthouses 7 . 10 Met Éireann is the national weather service in Ireland. They provide real time and past weather observations along with weather forecasts and rainfall radar images. This includes sea area weather forecasts and sea state observations 8 .
The OPW, in collaboration with the RPS Consulting Engineers and Met Éireann, are forecasting sea levels, tide and surge around the Irish coast. However this is not yet available to the public.
The Geological Survey of Ireland (GSI) 9 is responsible for acquiring geological data and providing advice and information 15 in all aspects of Irish geology. In conjunction with the National Emergency Coordination Centre, the GSI will develop tsunami hazard maps and emergency response plans for Ireland. This will ensure the safety of coastal communities in the unlikely event of a tsunami hitting the Irish coast.

Rescue Services
The RNLI is a charity that was established in 1824 and is operated largely by volunteers. It provides lifeboat search and rescue 20 services, seasonal lifeguards, water safety education and flood rescue response around the British Isles. There are 43 stations located around the island of Ireland.
The Irish Coast Guard is part of the Department of Transport, a department of the Irish government. Their overall objective is to reduce the loss of life on Ireland's seas, lakes, waterways and rivers, coastal and remote areas. Members are made up of both paid employees and unpaid volunteers. Unlike other countries, the Coast Guard in Ireland is not part of the defence forces. 25 However they are assisted by the Air Corps and Navy.  documented. This cannot be considered an exhaustive list, however it provides a benchmark to work from when considering how extreme waves impact Ireland. We hope that an accurate database can be established by combining this work with other sources. This is necessary in order to inform the future development of Ireland's marine resource and to protect the future of Irish coastlines and communities.
One of the major conclusions of this paper is that coastal flooding due to storm surges are common occurrences in Ireland 10 with 68 events documented in this catalogue. Note that these are only events where flooding of more than half a metre was reported. There are numerous storm surges where flooding of more than half a metre is likely to have occurred but was not reported, or events where flooding was less than half a metre but still caused huge damage or disruption. This highlights the need for accurate documentation of events as they occur. Coastal flooding brings major socio-economic impacts, so it is imperative that Ireland adequately prepares for such events now and into the future. 15 As found in O' Brien et al. (2013), rogue waves continue to be a common occurrence in Ireland with many people losing their lives as a result. Understanding the dynamics of these waves may reduce the associated risks in the future. However until then it is important that the public are educated on the subject and proper warnings are in place on dangerous stretches of coastline.
Storm waves also pose major risks and this paper has shown that many of the very large waves recorded on the buoy network are not rogue waves. Some of the largest waves recorded by Irish buoys are shown in Table 6, however the largest three should 20 be treated with caution as readings can become unreliable beyond a certain threshold. With increasing average temperatures globally and rising sea levels, it is still uncertain how the marine climate will adjust in the future. This is an area of ongoing research and of particular interest to Ireland given its proximity to the ocean and the frequency of extreme events.
Finally, without the vital services and volunteers of the RNLI, Irish Coast Guard and Community Rescue Boats, the number of deaths in Irish waters would be far higher. These services should continue to be well maintained and given proper recognition.