Why did so many of Dublin’s trees topple during Storm Betty?

On 19 August, the morning after Storm Betty swept through Dublin, Eddie Curran looked outside and saw that a large tree had fallen on his car.

Photos show his blue Ford Focus buried under the tree’s thick canopy. Curran says he wasn’t that surprised.

“Not really,” he says. “The thing with the trees is going on a long time.”

In recent years, roots of some trees in the Grace Park Meadows estate in Donnycarney have been pushing upwards and cracking up the pavement, says Curran.

Around a year ago, Dublin City Council workers came out to fix the pavements.

But as they drilled into the pathway with an electrical power tool, they also drilled through the roots, he says, so when the storm hit, it was easier for the trees to topple.

Dublin City Council is looking at that as a possible factor, says a report presented to councillors on the North Central Area Committee on Monday.

“Further investigation is also required to ascertain if road or pavement works or new services in the vicinity of failed trees might have damaged or severed roots and contributed to tree failures,” it says.

Another big factor though is the heavy rainfall, which meteorologists predict is only going to intensify as the climate changes. And that poses a conundrum for the city.

The council needs to find a way to balance the need for trees in the city with safety concerns that trees bring, said Social Democrats Councillor Catherine Stocker.

She had asked for the council report into Storm Betty because a lot of local residents are worried about whether the trees on their streets are dangerous, she says.

Fergus O’Carroll, a senior executive parks superintendent with Dublin City Council, said: “We are trying to align safety with what is coming down the tracks in terms of climate change.”

Dublin City Council has employed a consultant to inspect around 4,000 trees and will cut down any that pose a risk, he says.

“I love trees”

“We’re all very conscious of our desire to increase the tree canopy in the city,” said Stocker, the Social Democrats councillor, at the meeting of the North Central Area Committee on Monday. “I love trees and I want more trees in residential areas.”

The city needs trees too to soak up rainwater, says Stocker, but if trees can fall that easily there is a potential conflict emerging between safety and the environment.

On Tuesday morning, Curran pointed to the lighter concrete patches on the pavements in the Grace Park Meadows estate.

Those are where the council dug up and drilled and replaced the pavement, he says. “They definitely damaged the roots of the trees,” he says.

At least eight trees fell in Grace Park Meadows and neighbouring Grace Park Heights in Storm Betty, says Curran. Residents are seriously concerned about the safety of the remaining trees in any future storms, he says.

The bonnet of his car was damaged and his windscreen was broken. Other trees fell into people’s gardens, photos show. “It’s very, very lucky that no one was injured,” says Curran.

At Monday’s meeting, Fine Gael Councillor Naoise Ó Muirí tabled a motion calling on the council to carry out an “urgent tree assessment and replacement programme for the Grace Park Heights Estate, as trees there are particularly vulnerable to collapse, as evidenced in the recent storm”. The motion was agreed.

Fianna Fáil Councillor Tom Brabazon says he had to walk home during Storm Betty because he was unable to get a taxi and the trees were dangerous on the night. “The lower branches were whipping around,” he says. “They would take the eye out of your head if you were not careful.”

O’Carroll, the parks superintendent, said it is important that the council doesn’t “go mad” cutting down trees. He agreed with Stocker that the council has to strike a balance between the need for trees in the city and human safety, he says.

How to do that? “That is the $64m question,” he says.

The council has a programme for managing trees. “They are actively managed to keep them as safe as possible,” says O’Carroll.

A tree that might live for 80 to 100 years in the countryside would be cut down in the city after 50 years,  he says.

Consultant the council has contracted should be done inspecting trees across the city, including in Grace Park Heights, by the end of the year, O’Carroll said.

That consultant’s work will feed into the council’s digital inventory of trees in the city. “The inspection reports will come with recommendations and they will be followed,” he says.

The most urgent works will be done first, he says. In some estates, the council might have to cut down a lot of trees, says O’Carroll. If that happens it will replant others in their place, he said.

At the area committee meeting on Monday, Green Party Councillor Donna Cooney said the council needs to look at “future-proofing trees”.

The roots should have as much space as the size of the canopy, she says, so in many cases, the trees in Dublin should be further apart from each other.

The council report notes that “trees growing in tight spaces and/or in compacted soils are considered more likely to wind throw”.

This needs to be examined as “a significant number of trees that failed were growing in smaller concrete tree pits”, says the report.

More rain

“What happened with Betty was interesting for the greater Dublin area,” says Paul Moore, a climatologist with Met Éireann. “A few circumstances came together that led to the number of trees down in the greater Dublin area.”

It was the strongest August wind in 35 years, he says, coming after the wettest July on record.

Summer storms often knock down more trees than winter storms because tree canopies are thick with leaves and fruit and so are top heavy, he said. They sway more in the wind, which can uproot the tree, said Moore.

The strength of the wind that came with the summer storm isn’t an indicator of climate change, says Moore. It’s not unusual to get strong winds in August because Ireland can get the tail ends of hurricanes.

In 1986, the end of Hurricane Charlie brought a lot of damage to the eastern part of the country, he says. “There is no long-term trend there to say that winds are getting higher.”

But rain is another question.

Average rainfall in Ireland increased 7 percent when comparing the most recent 30-year period to the previous 30 years, says Moore. And there has been an increase in summer rain too, he says, with a 20 percent increase on average for July, he says.

The Intergovernmental Panel on Climate Change predicts that higher temperatures will mean more moisture in the atmosphere and in turn that will lead to more rain, he says.

Because soil moves more when it is very wet, increased rainfall before a storm can mean more trees are uprooted, he said.

The council report says the heavy rainfall on the night of Storm Betty may have increased the weight of the trees’ canopies too, which were already full because it was summer.

“Such full canopy acts as a sail, dramatically increasing the wind loading on the trees as compared to if the same storm struck during the winter months,” says the report.

“It is also considered possible that the level of rain that fell that night also increased the loading on the tree structure exacerbating the effects of the strong winds,” it says.

Back in Grace Park Meadows, Curran says he wouldn’t be sorry if the council replaced the trees in his estate with another type.

The trees they have drip a lot of sap, and he’s not convinced they are the right variety for residential streets, he says.

“Maybe if the council had a maintenance programme for when these trees are growing,” he says. “It must be a city-wide problem.”