‘Once in a 100 years’ extreme weather event caused Donegal flooding

A "once in a 100 years" extreme weather event was responsible for the widespread flooding and devastation that struck the northwest, according to Met Éireann.

The suddenness and scale of rainfall overwhelmed drainage systems and destroyed older bridges in Co Donegal. It was concentrated on the Inishowen peninsula over a two-hour period from 7pm to 9pm on Tuesday, according to meteorologist Gerry Murphy of Met Éireann.

Malin Head had 63mm of rain within a six-hour period. "It was the intensity of the rainfall that was too much for waterways [and] for drainage systems that weren't adapted for them," he said.

An average wet day results in 25mm of rain in a 24-hour period. A country-wide orange thunderstorm alert with associated with heavy rainfall issued at 11am on Tuesday.

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“The track of the thunderstorms was such that basically they all converged on the Inishowen peninsula and that gave the extreme amounts of rainfall in the short period,” he told RTÉ News at One. Other parts of the midlands and northwest also experienced heavy rainfall but not to the same extent.

“The tail-end of Hurricane Gert was a factor. Winds are normally associated with hurricanes but in this instance the weather system was weak,” he added.

However, it brought moist, humid air which mixed with colder air from the west which sparked off exceptionally intense thunder storms. “The track of the thunderstorms was such that it poured relentlessly on the northwest, especially the Inishowen peninsula.”

Turbulent storms

Met Éireann's climate team had analysed the rainfall and said there was “a return period” of about 100 years.

Climate research indicates more frequent extreme weather events will occur, including more turbulent storms and more intense rainfall incidents and resulting flooding, are inevitable as a consequence of global warming. The recent thunderstorms would, however, be classified as a single event within the normal variability of weather patterns, and as such cannot be blamed on a warming world.

Unusually, climate scientists concluded that human-caused climate change dramatically increased the likelihood of the extreme heatwave in much of Europe during June this year. The analysis was carried out by World Weather Attribution (WAA), an international coalition of scientists that calculates the role of climate change in extreme weather events.

They combined temperature records and the latest observations with a series of sophisticated computer models to calculate how much a global rise in greenhouse gas emissions had raised the odds of the soaring temperatures. Such temperatures will become the norm by 2050, the WAA warned, unless action is taken to rapidly cut carbon emissions.