WEATHERMAN'S VIEW:Increased rainfall will pose new problems, writes Tim O'Brien
IRELAND WILL have to plan and build high capacity storm drains and flood defences along major roads and in housing estates to cope with weather conditions like those over the past week.
Met Éireann's deputy chief forecaster Gerald Fleming says sudden, heavy rainfall, such as the 43mm which fell at Dublin airport in 90 minutes last Saturday evening, is likely to be a recurring event.
Speaking to The Irish Times yesterday, Mr Fleming said the likelihood of more heavy rain was connected to the relationship between temperature and moisture.
As the temperature increases the capacity of air to hold moisture increases. But this is not a "linear" relationship, he explained.
"If you get a 1 per cent increase in temperature you could get an increase in moisture of about 20 to 30 per cent, so temperature increases can easily lead to heavier rain." In the past, rain like last Saturday's would have been considered a "one in 125 year event" on a statistical basis, but recent trends in global warming resulting in an increase in temperature, would suggest the trigger for heavy rain may be more easily reached in coming years.
While some local authorities last week claimed they could not have predicted such an event, Mr Fleming says planners will have to think in the longer term.
"In Catalonia [in northeast Spain] they have storm drains which are capable of taking a 400mm flash rainfall - our total on Saturday amounted to 76mm of rainfall.
"The storm drains in Catalonia are unused 95 per cent of the time but they are there when they are needed.
"These are the kind of things we have to put in place if we are to avoid flooding" he said.
Mr Fleming added that builders and property developers have taken "too short a view" of what might happen or simply considering that a one in 100 year event was not worth fighting. But the implications of this for the Government are severe.
In addition to requiring that all new roads and housing developments have weather defences, the State may have to suffer the cost of retrofitting storm drains to many suburbs, towns and cities - as well as new motorways.
The National Development Plan set aside some €382 million for flood defences but a recent Dáil question tabled by Labour's environment spokeswoman Joanna Tuffy elicited the information that just €16 million was spent in 2005, €14 million in 2006, and €23 million last year.
Ms Tuffy maintains this money was for the "known problems" including coastal protection which were evident when the plan was being formulated. But she said the cost of dealing with last week's occurrences on a regular basis may run to well over a billion euro.
"Despite the work of the Office of Public Works in implementing some of the recommendations of the Flood Strategy Review Group, including the mapping of flood hazard areas, there has been no major changes in how the authorities manage flood risk" she said.
A spokesman for the OPW said it could not comment on the budget for flood defences as all personnel with that information were at meetings to discuss the recent heavy rainfall.