Environment

Clifden flooding a stark warning of extremes to come in Ireland - climate expert

Many Irish towns susceptible to ‘catastrophic’ floods due to catchment around river

Patrick Guy at the back of his house at Riverside beside the Owenglen River as water pours down the waterfall after the earlier flooding. The entrance driveway beside Patrick’s house was completely destroyed by the flooding. Photograph: Joe O’Shaughnessy.

Brian Hutton
Thu Sep 3 2020 - 19:58

The flooding that swamped Clifden in Co Galway within hours is a stark signal that Ireland’s weather extremes will continue to get worse, one of the country’s foremost climate change experts has warned.

Prof Peter Thorne said a “very large” number of towns and villages around the country are similarly susceptible to “truly catastrophic” flash floods because of their catchment around a river.

Playing down speculation that drainage in State-owned Sitka spruce plantations outside Clifden were to blame for Wednesday morning’s flood, Prof Thorne said it was down to the “tail end of Hurricane Laura” crashing into mountains around the coastal Conneamara town.

“When you have all that tropical, deep moist atmosphere, travelling across a silky, smooth Atlantic, the first thing it does is hit the mountains and hills by Clifden, and it is like squeezing a sponge,” he said.

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The Maynooth University academic, who was lead author on the fifth assessment report of the UN’s Intergovernmental Panel on Climate Change, said the ground was also “unseasonably saturated” as each of the last three months was wetter than normal.

Small rivers like the Owenglin in Clifden are also “very sensitive to high rainfall”, he said.

Pointing to the devastating impact of small rivers swamping parts of Inishowen, Co Donegal in August 2017, Prof Thorne said many towns and villages face a similar fate, which historically happens every few years .

“The climate is one degree warmer than it was in the 19th century because of man-made emissions, and for every degree rise in temperature the atmosphere holds seven per cent more water,” he said.

“Fundamentally, what goes up must come down. With more water in the atmosphere, when it rains, it rains with greater intensity.”

Climate model projections “robustly” suggest that trend will continue.

“It is getting worse and will continue to get worse until we can manage to stabilise global temperature changes,” he added.

“There is no good science on whether the frequency (of flooding events) will increase, but the intensity of events will be worse — it is a case of getting used to the idea that our extremes will be more extreme.

“Something once seen as a once in a century event nationally might become a one in a 20 year event.”

At the time of the Clifden flooding, only a yellow rain warning was in place for counties Donegal, Leitrim, Mayo and Sligo.

Evelyn Cusack, head of forecasting at Met Éireann, said it was a “forecast failure” which was in part down to its modeling systems, which “have a little difficulty” predicting rain from a tropical air mass, which are unusual in Ireland.

“It was a forecast failure in terms of the rainfall amount, but Met Eireann would not be predicting floods or the river flow,” she said. “We wouldn’t be predicting the impact.” Met Eireann had forecast 20 mm rainfall in the area, when around 60 mm fell overnight.

Following the surge in water at Clifden, which forced the evacuation of homes and two schools, claims emerged on social media that drainage on large tracts of bog outside the town which have been converted to Sitka spruce plantations, run by Coillte, contributed to accelerating the flooding.

But Dr Tiernan Henry, a geoscientist and surface water expert at NUI Galway, said he would be “very reluctant to point the finger at forestry”.

Records at nearby Mace Head weather station showed 27 mls of rain falling within three or four hours, he said. “That is essentially a quarter of the average monthly rainfall for September in that area happening in just a few hours,” he added.

“It was a very intense rainfall event.” Dr Henry said the “single biggest factor” was the “unusual amount of rain” falling on a relatively steep catchment onto a “flashy river”.

Coillte also disputed the speculation. Pat Neville, communications manager at semi-state forestry company, said it operates two plantations near Clifden, which were identified on social media as being culpable.

Water drains from the larger of the two plantations away from Clifden, he said, adding that drains in the forests are shallow and would have long since “clogged up” with debris as they were planted more 40 years ago and are not maintained.

“We had an extraordinary amount of rain in a short time. To point the finger at planting, to say that was the cause of the flooding event in Clifden, would be quite unfair,” he said.

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