Dublin City Council is already preparing for predicted climate change, writes Liam Reid, Environment Correspondent
It is not up there with the receding glaciers of the Alps or the melting snow cap of Kilimanjaro, but at the Vartry Reservoir, high in the Wicklow hills, the signs of global warming are also becoming apparent.
The reservoir has been supplying water to the greater Dublin area for more than a century. Throughout that time, Dublin City Council, which operates the reservoir, has been taking meticulous records, including the amount of rain that falls on the site every month. Worryingly, council officials have been noticing changes in recent years. While the annual average rainfall has remained the same, the last two decades have seen the pattern of rainfall change significantly, with rain falling in much shorter, more intense bursts.
The records show that some months have seen a 300 per cent increase in rainfall above the average of earlier years. Winter months have become much wetter, while summer months have become much drier. For many it might be a statistical anomaly, but this rainfall pattern, which is predicted to continue, has huge implications for Dublin city.
Back in the city centre, at the offices of Dublin City Council, Tom Leahy is dealing with these implications. As deputy city engineer with responsibility for strategic planning, his job is to "future proof" Dublin. At present, his office is preparing a series of projects and proposals, running into billions of euro, to protect the city against the worst impacts of global warming, as they begin to take their toll over the coming decades.
"The climate is changing, and we have to identify the possible long-term impacts and how they can be addressed," he says. "It's not going to happen overnight, so we have plenty of time to plan and implement the necessary measures." As a low-lying coastal city on a plain next to a mountain range, and with three rivers running through its heart, Dublin is a prime candidate for flooding, at the best of times. However, the climate-change side effects of intense rainfall highlighted at Vartry, combined with higher sea levels, will put the city at much greater risk in the future.
The potential future for Dublin was seen in 2002, an annus horribilis for the capital, when it suffered from three of the main sources of flooding, from the sea, from rivers and freak flash flooding. The disastrous year began on February 1st, when a combination of elements, including stormy weather, atmospheric pressure and high tide levels, brought about a tidal surge. The water levels in Dublin Port were the highest ever recorded, and sea water swept in and flooded chunks of residential areas close to Dublin Port and the south docks. There was also a number of incidents of highly localised torrential rain showers where the drainage system could not cope and the areas flooded. The final floods of the year occurred in October when a major storm saw the rivers of Dublin swollen from storm water. The Tolka burst its banks and flooded hundreds of houses in the Drumcondra area. None of these incidents can be attributed to global warming, but what is absolutely certain is that such incidents are increasingly likely in the future because of climate change.
Flooding is viewed by experts as a natural event and one which is impossible to eradicate fully. In terms of Dublin City Council's plan on future proofing the city from climate change, the aim is to ensure the incidence of flooding does not increase. "The objective is to reduce flooding risk to 1 per cent, or one in a hundred year event across the city," Tom Leahy explains.
Significant work has already taken place to protect the city against fluvial or river floods. In recent decades the Liffey, Dodder and Tolka have all caused significant damage through flooding in the greater Dublin area. In the last four years, in the wake of the October 2002 floods, the council has undertaken a multi-million euro set of works, which have almost been completed. These have involved the construction of higher banks in Griffith Park and other measures.
MAJOR WORK WAS also carried out on the Dodder in the 1990s to prevent the flooding that occurred in the wake of Hurricane Charlie in 1986 and further work is expected. According to Dr Rowan Fealy, a climatologist at NUI Maynooth, and part of a team that has developed much of the predictions on climate change and its impact on Dublin and the rest of the country, flooding from rivers will continue to be a risk. The issue as he sees it is that an increasing number of flood plains further upriver are being built on. The water has nowhere to be stored and is forced downstream, flooding areas much closer to the coast. "You saw this with the Tolka at Dunboyne, where there was a lot of development," he says.
The changing pattern of rainfall will add to this risk, leaving more water to be dealt with by rivers at certain periods of time. This more intense rainfall also increases the risk of flash flooding. According to Tom Leahy, intense local rainfall is another issue the city council is grappling with. These freak showers can deliver a month's worth of rain over a small area of the city in a matter of hours, in an area where the 19th century drains simply cannot cope.
Climate change was factored into a major study of the city's drainage system, which was carried out in recent years. The study was necessary because of the age of the drainage system and the needs of the growing city. A €2.5 billion drainage programme will build in capacity to deal with flash flooding, beginning in the next few years in Rathmines and Dublin south-east, where a €70 million project is planned.
New developments in Dublin are also being required to include drainage that is designed to store water on site in smaller modern-day versions of ditches, so that the water can be released slowly into the drainage pipe system.
However, in the long term the sea poses the greatest threat to the city. Large-scale sea-level rises of more than one metre could place sections of some of the most expensive parts of Dublin at risk, as far inland as Merrion Square and Government buildings. Even in this century, more modest sea-level rises of half a metre will also have an impact when combined with tidal surges.
Dublin City Council has already been preparing for this. The first element of their plan is already in place. Called the Safer project, it is an early warning system based around a complex computer programme, which combines information on weather conditions and tide levels to predict when there is a risk of a tidal surge. The system, introduced in the aftermath of the February 2002 floods, provides a warning of potential flood conditions four days in advance. According to Leahy, this time is vital to enable an adequate emergency response to minimise the impact of the flooding on households and businesses in prone areas around Ringsend and the docklands areas of the city.
The second element of protection against the sea involves more than €100 million of flood-protection works. These works have already begun with the construction of barriers at Spencer Dock to minimise the flooding impact. The council is also planning to improve some of the sea-wall defences along the coast. The idea is to integrate these defences with a new promenade and bicycle way, which is planned for the area between Sandycove and Sutton. In addition to these defences, pumping facilities at various vulnerable stretches are also in the pipeline. It is envisaged that these defences will protect Dublin against sea-level rises for at least 30 years.
However, there is a major question as to whether they will be sufficient in the long term to protect against large sea-level rises. As a result, a new study, which got under way this year, will examine whether the city should build a new, much costlier and more dramatic set of defences, called tidal barrages. Tom Leahy describes the project as being at "pre-feasibility stage". The council has christened the study Project 2030, as it does not believe the barrages will be needed for at least 25 years. "What we are looking at is the possibility of a series of barrages, as opposed to just one," explains Leahy.
Bull Island, which is only 150 years old and was formed following the construction of the north and east walls in Dublin port, already acts as a natural barrage for the city. The sites for the new barrages include one between the north and south walls of the port, another between Bull Island and Sutton, and a third north of Howth Head. "What we have to find out is if these are feasible in any way," Leahy says.
It is perhaps an irony that, given the amount of work needed to keep Dublin from flooding, the second major challenge of climate change is actually a lack of water. With the population of the greater Dublin area expected to grow to close to two million people by 2020, water shortages are now seen as a major threat. While total average rainfall has remained fairly consistent on the east coast, climate models predict that it will become drier, and with existing water sources, such as Vartry and Poulaphouca, now at their capacity, the essence of the problem will be less water to cater for far more people.
THE COUNCIL IS now examining two options to deal with the shortage, which is predicted to kick in from 2020. The first is to construct a large desalination plant in Dublin Bay. However, the cost of operating the plant, combined with the taste of desalinated water, makes this a less likely option, although the council insists no decision will be made until mid 2008.
The second and more likely option is the construction of a €500 million water mains to pipe water more than 100 kilometres from the Shannon river system, most likely Lough Ree. A decision is expected on the two options by the middle of next year, with the aim of having the new water source in place by 2016.
NUI Maynooth's Dr Rowan Fealy believes such a pipe will prompt a huge question on how increasingly scarce freshwater sources, even in Ireland, should be used. "In the west there will be wetter winters, but a number of consecutive dry summers could see water shortages there. The question is then, who gets the water? What we need to put in place is policy structures to deal with these kinds of questions, which will crop up," Fealy says.
