Coastal flood risk Ireland
Sea level rise in Ireland
Variation in the late Quaternary ice loading of Ireland has led to a north-to-south gradient in isostatic crustal movements, resulting in predominantly emergent coasts in northern areas and changing southwards to coastal environments that are submergent to ‘‘apparently stable’’. Relative sea level for Ireland is rising 1 mm/y on average, although there are significant regional variations (9). At present, there are no apparent effects of climate warming on SLR (10).
Belfast is rising as a consequence of glacial isostatic adjustment. This adjustment is occurring at a rate that, from the data, appears to be exceeding current sea level rise. This is observed as a local drop in sea level. Dublin and Malin Head are also emerging. However, the rate of emergence is outweighed by sea level rise. This results in a small change in sea level, relative to the global average. Sea level at Dublin is currently rising by 0.23 mm per year (1).
Central estimates of relative sea-level rise for Belfast are 7.8cm by 2020, 18.6cm by 2050 and 40.3cm by 2095 (11).
Global sea level rise
For the latest results: see Europe Coastal floods
For the latest results: see Europe Coastal floods
Extreme water levels - Global trends
More recent studies provide additional evidence that trends in extreme coastal high water across the globe reflect the increases in mean sea level (15), suggesting that mean sea level rise rather than changes in storminess are largely contributing to this increase (although data are sparse in many regions and this lowers the confidence in this assessment). It is therefore considered likely that sea level rise has led to a change in extreme coastal high water levels. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water levels via mean sea level contributions. While changes in storminess may contribute to changes in sea level extremes, the limited geographical coverage of studies to date and the uncertainties associated with storminess changes overall mean that a general assessment of the effects of storminess changes on storm surge is not possible at this time.
On the basis of studies of observed trends in extreme coastal high water levels it is very likely that mean sea level rise will contribute to upward trends in the future.
In Ireland, flooding is associated mainly with heavy rainfall which can lead to enhanced river-flow and over-topping of river banks. However, coastal flooding events also cause devastating effect, particularly those associated with storm surge events that occur in combination with spring tides. The effects may be enhanced locally by the coastal topography (3).
According to the IPCC report (2007), there is likely to be an increase in the number of intense cyclones and associated strong winds, particularly in winter over the North Atlantic; a slight poleward shift of the storm tracks is also likely. These changes will have a direct impact on storm surges, which are primarily caused by low pressure and strong winds. Rising time-mean sea levels will enhance the impact of surges. According to the research of Lowe et al. (2001), along the south Irish Sea coast the surge height is dominated by the low pressure effect, with the wind forcing providing only 16% of the surge height. In the north Irish Sea, on the other hand, the wind forcing contributes 72% of the surge height (2).
Under enhanced greenhouse gas conditions extreme wind speeds could increase by 10% in the North Sea resulting in a similar increase in the extreme storm surge (4). A statistically significant increase in extreme storm surge along the UK coastline has been found under assumed future climate conditions (5). Storm surge extremes may increase along the North Sea coast towards the end of this century (6,25,26).
Wang et al. (2) made model projections of climate change impact on storm surge in the Irish Sea. They ran a model for two 30 year time-slice periods (1961–1990 and 2031–2060). They used a climate change scenario characterized by low population growth, rapid economic growth and rapid introduction of new and efficient technologies (the so-called SRES A1B emission scenario in the IPCC report of 2000). The atmospheric CO2 concentration in this scenario reaches 720 ppm at the end of 21th century and the global mean temperature will rise about 3.8 degrees Celsius by the end of this century (relative to the mean temperature between 1961 and 1990). From their analysis Wang et al. (2) concluded that their model is capable of reproducing storm surge events with reasonable accuracy, supporting its use as a suitable tool in climate change studies.
For 2031–2060 relative to 1961–1990 changes (%) in the annual mean wind speed are relatively small; there is an increasing tendency along the west and north-west coast of Ireland and part of the UK coast, but a decrease over the open sea. For the difference changes of mean sea level pressure, the distribution pattern shows an increase around Ireland and to the south, and a decrease to the northwest. This is consistent with an increase in the frequency of intense cyclones over the area in the future (2).
Wang et al. (2) show that storm surge heights in the range 50–100 cm are increasing in frequency around all Irish coastal areas from 1961–1990 to 2031–2060; up to 20% in the west and northwest. There is also a significant increase in the height of the extreme surges along the west and east coasts, with most of the extreme surges occurring in wintertime. Changes in extreme surge heights also appear to be related to changes in extreme wind speeds and mean sea level pressure. There are also significant changes in the return values of surge heights.
The relative changes of the 10-year and 50-year return period of the surge heights between the future and control simulation show that along most of the Irish coastline the trend is for increasing surge height. However, the spatial pattern of the change is far from uniform. There is some correlation between changes in the maximum wind speed and changes in extreme surge heights but this does not apply everywhere; in the 50-year return values the extreme storm surge heights decreased along the north coast while the maximum wind speed increased; changes in the wind direction may be a factor in this case (2).
Due the complex bathymetry in the continental shelf area, some non-local surge propagating along the coast also caused the discrepancy between the surge height and wind speed. The significant test results show that large fraction of the extreme surge heights in the southern Irish sea area are significant at 10% level, while almost non-significant in the northern area, which is totally different from the extreme wind speed distribution (2).
Storminess along Irish coast will probably decrease
It is highly uncertain how winter storm tracks over the North Atlantic Ocean may change under climate change this century (28). Following the general consensus in the literature to date, the average wind changes over the North Atlantic by the end of the century are small and negative and less than the high natural interannual variability of the region (29). Natural variability is large and dominant and is projected to remain so for the century to come.
A recent study shows that mean wind speed at 10 m height will decrease this century up to 3% over the North Atlantic Ocean for all seasons under moderate (RCP4.5) and high-end (RCP8.5) scenarios of climate change. This study was based on global climate model projections for the period 2070 - 2099 compared with 1980 - 2009. The study also shows that wind extremes and storminess over the North Atlantic Ocean will also decrease: the 5% strongest winds (the so-called 95th percentile of all wind speeds) will decrease by up to 15%. Wind climate changes over the North Atlantic Ocean not necessarily reflect future changes in wind climate over Ireland, however: the projected decreases in the frequency and intensity of wind storms crossing Ireland are not statistically significant (27).
As a result future waves will be somewhat lower as well
This changing wind climate over the North Atlantic Ocean results in changes in wave climate. A measure to describe the wave climate is the so-called ‘significant wave height’, defined as the mean height of the highest third of the waves. Overall along the Irish coast, the annual and seasonal means of this ‘significant wave height’ will probably decrease, up to 10% by the end of this century. The same holds for larger ‘storm-waves’ (27). This estimate of a future reduction of ‘significant wave height’ in the North Atlantic Ocean agrees with previous studies (30). One should be aware, however, that in addition to wind climate projections, wave climate projections are also uncertain for this region (28,31).
The largest waves ever recorded in Ireland, with a buoy network set up in 2000, are 25 m (in 2014), 26.1 m (in 2017) and 30.96 m (in 2016), though the latter may be a suspicious reading (32).
Coastal flood probability
Between 1961 and 2006 40 periods have been identified where coastal flooding was generated in Ireland, a major coastal flooding event being defined as an inundation in excess of 0.5 m of an otherwise dry coastal area. The inundation levels varied from 0.5 m to a couple of metres (32).
Under future scenarios of global warming, the current 100-year extreme water level is likely to reoccur every 1–2 years with the sea levels predicted for 2100 (medium value for sea level rise of 0.48 m) (1).
The effect of a sea level rise on estuaries will tend to enlarge their vertical and horizontal extent, resulting in the penetration of tides further upstream. The outflow from rivers would be impeded as a consequence, which, in a high intensity rainfall event where runoff is high, would increase the risk of flooding (1).
Potential coastal damage
Ireland is quite fortunate in that the effects of sea level rise on the coastline may not be felt as severely as in some other countries in Europe. Areas in the south of the country are likely to feel the effects first, particularly low-lying coastal locations with little or no natural protection and located on ‘soft’ or easily eroded material. In Ireland, the impacts of sea level rise will be most apparent in the major cities of Cork, Limerick, Dublin and Galway (1).
Economic impacts of sea level rise for Europe
The direct and indirect costs of sea level rise for Europe have been modelled for a range of sea level rise scenarios for the 2020s and 2080s (16). The results show:
- First, sea-level rise has negative economic effects but these effects are not particularly dramatic. In absolute terms, optimal coastal defence can be extremely costly. However, on an annual basis, and compared to national GDP, these costs are quite small. On a relative basis, the highest value is represented by the 0.2% of GDP in Estonia in 2085.
- Second, the impact of sea-level rise is not confined to the coastal zone and sea-level rise indeed affects landlocked countries as well. Because of international trade, countries that have relatively small direct impacts of sea-level rise, and even landlocked countries such as Austria, gain in competitiveness.
- Third, adaptation is crucial to keep the negative impacts of sea-level rise at an acceptable level. This may well imply that some European countries will need to adopt a coastal zone management policy that is more integrated and more forward looking than is currently the case.
Adaptation strategies – Ireland
According to the Environmental Protection Agency (1) a sensible approach to coastal management for sea level change is
- no new building or new development within 100 m of ‘soft’ shoreline,
- no further reclamation of estuary land,
- no removal of sand dunes, beach sand or gravel,
- all coastal defence measures to be assessed for environmental impact. Where possible, the landward migration of coastal features, such as dunes and marshes should be facilitated. These features form an integral part of the coastal system, physically and ecologically, and provide protection against wave energy through dissipation.
The Agency states that a policy of planned retreat in some areas, combined with prohibitions on new developments in vulnerable coastal zones offers the best economic solution for most areas in Ireland.
The Planning and Development Act, 2000 was introduced to ensure that the Irish planning system can face the challenges meeting the country as it continues to grow and prosper. The Act provides that a planning authority’s development plan may include objectives for, inter alia: regulating, restricting or controlling development in areas at risk of flooding (whether inland or coastal), erosion and other natural hazards; regulating, restricting and controlling the development of coastal areas and development in the vicinity of inland waterways; regulating, restricting and controlling development on the foreshore, or any part of the foreshore (7).
Improve flood warnings
Systems for forecasting surges and issuing coastal flood warnings where appropriate are urgently needed. New methodologies may be needed to assist engineering calculations and flood forecasting, and a reliable tide gauge network with quality controlled data processing and archiving (8).
Adaptation strategies - The costs of adaptation
Both the risk of sea-level rise and the costs of adaptation to sea-level rise in the European Union have been estimated for 2100 compared with 2000 (17). Model calculations have been made based on the IPCC SRES A2 and B1 scenarios. In these projections both flooding due to sea-level rise near the coast and the backwater effect of sea level rise on the rivers have been included. Salinity intrusion into coastal aquifers has not been included, only salt water intrusion into the rivers. Changes in storm frequency and intensity have not been considered; the present storm surge characteristics are simply displaced upwards with the rising sea level following 20th century observations. The assessment is based on national estimates of GDP.
The projections show that without adaptation (no further raising of the dikes and no beach nourishments), the number of people affected annually by coastal flooding would be 20 (B1 scenario) to 70 (A2 scenario) times higher in 2100 than in 2000. This is about 0.05 - 0.13% of the population of the 27 EU countries in 2010 (17).
Without adaptation, damage costs would increase roughly by a factor of 5 during the century under both scenarios, up to US$ 17×109 in 2100. Total damage costs would amount to roughly 0.04% of GDP of the 27 EU countries in 2100 under both scenarios. Damage costs relative to national GDP would be highest in the Netherlands (0.3% in 2100 under A2). For all other countries relative damage costs do not exceed 0.1% of GDP under both scenarios (17).
Adaptation (raising dikes and beach nourishments in response to sea level rise) would strongly reduce the number of people flooded by factors of 110 to 288 and total damage costs by factors of 7 to 9. In 2100 adaptation costs are projected to be US$ 3.5×109 under A2 and 2.6×109 under B1. Relative to GDP, annual adaptation costs constitute 0.005 % of GDP under B1 and 0.009% under A2 in 2100. Adaptation costs relative to GDP are highest for Estonia (0.16% under A2) and Ireland (0.05% under A2). These results suggest that adaptation measures to sea-level rise are beneficial and affordable, and will be widely applied throughout the European Union (17).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Ireland.
- Environmental Protection Agency (2003)
- Wang et al. (2008)
- Wells (1997), in: Wang et al. (2008)
- Flather and Smith (1998), in: Wang et al. (2008)
- Lowe et al. (2001), in: Wang et al. (2008)
- Woth et al. (2005), in: Wang et al. (2008)
- Department of the Environment, Heritage and Local Government (2010)
- Irish Academy of Engineering (2009)
- Devoy (2008)
- Devoy (2000a, 2000b), in: Devoy (2008)
- UKCIP09 UL Climate Projections 09, in: Northern Ireland Environment Agency (2009?)
- Bindoff et al. (2007), in: IPCC (2012)
- Church and White (2011), in: IPCC (2012)
- Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
- Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
- Bosello et al. (2012)
- Hinkel et al. (2010)
- Cazenave et al. (2014)
- IPCC (2014)
- Watson et al. (2015)
- Yi et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Shepherd et al. (2012), in: Watson et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Vousdoukas et al. (2016)
- Brown et al. (2010, 2012); Debernard and Røed (2008); Lowe et al. (2009), all in: Vousdoukas et al. (2016)
- Gallagher et al. (2016)
- Church et al. (2013), in: Gallagher et al. (2016)
- Collins et al. (2013), in: Gallagher et al. (2016)
- Dobrynin et al. (2012); Hemer et al. (2013b), both in: Gallagher et al. (2016)
- Woolf and Wolf (2013), in: Gallagher et al. (2016)
- O’Brien et al. (2018)