Is climate change causing the recent floods along the St. John River?

As water levels rose along the St. John River this spring, many New Brunswickers had two reactions.

First, they prepared urgently for the flood.

Then they asked themselves whether this was evidence of climate change whether two major floods in two years proves that human activity has altered the forces of nature.

"Things have certainly changed," Elaine Price of Mill Cove said as she watched the water rise toward her home last month.

In Chipman, Rhonda Saulnier was asking the same question.

"It's unbelievable," she said.

"So now that it's happened two years in a row, like everybody I'm afraid it's the new norm. I'm praying it's not."

Water levels peaked in Fredericton on April 23 at 8.36 metres, compared witha peak of 8.31 metres last year. In Saint John, the peak was 5.53 metres compared with 5.76 metres last year.

For the second straight year, homes were evacuated. For the second straight year, the Trans-Canada Highway was closed downriver from Fredericton.

Even officials who oversee flood response seemed taken aback.

Is flooding along the St. John River the new norm?

5 years ago

Duration 1:27

For two years in a row, floodwater reached historic levels along the lower St. John River system.

"When this event happened last year, we were under the impression this was a historical event, and two years in a row, the historical event happened," said Ahmed Dassouki, the director of operations at the Department of Transportation and Infrastructure.

"It's a new day, and two years in a row is telling us we can't just do the same thing," Premier Blaine Higgs told reporters.

Yes, this is climate change probably

Is this climate change?

The answer isn't straightforward, but the consensus is: yes, probably, likely.

"You can't attribute one event to climate change," said Barrie Bonsal, a senior research scientist with Environment Canada, who co-authored a major report on climate change released last month.

"But as we warm the atmosphere, and we see associated impacts, we are increasing the probability of certain types of events that are associated with warming."

But if climate change was a factor in the back-to-back floods, so was luck.

"Climate change is a larger trend that says that these kinds of things will happen more often," saidJasmin Boisvert, a provincial hydrologist. "With two floods of this magnitude, there has to be an element of bad luck, for lack of a better word."

Bonsal said with warming temperatures, it's likely there'll be less snow pack at the end of most winters.

But when there happens to be a lot of snow pack, as there was this year, the trends caused by climate change those warmer temperatures and increases in extreme rain make flooding more likely.

Human activity causing warming

The report Bonsal co-authored, Canada's Changing Climate Report, says temperatures in Canada warmed by 1.7 C between 1948 and 2016 and will continue to get warmer.

More than half of that trend is "likely" due to human activity, the report adds, and that trend "has increased the likelihood of some types of extreme events."

Scientists have been forecasting the impact of warmer temperatures for decades, but until recently their projections felt abstract and theoretical, and not very local.

Now it's real. Recent weather events, Bonsal said, are "eerily consistent" with those previous projections.

'Entirely attributable'

Those whose businesses depends on knowing what is coming agree.

"What we have seen is entirely consistent with what global modelling has predicted," said Craig Stewart, a vice-president with the Insurance Bureau of Canada, which has seen flood and wildfire payouts soar in the last decade.

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"They have predicted that we would see increased annual precipitation and incidents of extreme rainfall in eastern Canada, and more droughts and wildfires in western Canada, and that is exactly what we are seeing play out," Stewart said.

"So in our minds, we attribute current events to climate change. The trends we are seeing are entirely attributable to climate change."

More rain, bigger floods

What happens next? It gets worse.

"We'll see more flooding like this," Boisvert said. "That is the general trend."

In worst-case scenarios, precipitation in Atlantic Canada is expected to increase five per cent by 2050 and 12 per cent by the end of the century.

Among the federal report's other forecasts:

• Across Canada, extreme-precipitation events that happen once every 20 years will occur every 10 years between 2031 and 2050 if carbon dioxide emissions continue to grow.
• By the end of the century, extreme events that happen once in 50 years will happen every 10 years. "The more extreme the event, the more frequency will change," the report says.
• In New Brunswick, there will be an "increase in flood and drought frequencies" in Saint John, Nashwaak, Canaan, Kennebecasis, Restigouche and Miramichi watersheds.

The federal report cites a study by University of Moncton professor Nassir El-Jabi, who teaches hydrological engineering.

The rate and magnitude of climate change under high versus low emission scenarios project two very different futures for Canada.- Environment and Climate Change Canada

El-Jabi estimates "low-return" floods in the province frequent minor floods will see water levels increase 30 to 55 per cent.

"High-return" floods like the ones seen in 2018 and 2019 will grow more slowly, but could still be 21 per cent bigger by the year 2100.

Some caveats

There are caveats to all of this.

"These changes take effect slowly, over time, and the nature of weather is that it is very variable," Boisvert said.

"You might get extreme years in some years and not in other years."

A river system is dynamic, so other factors such as forestry and agricultural run-off, or construction that affects drainage can play a role.

Rather than link specific events to climate change, scientists are focusing on a new field called "event attribution."

It looks at how the probability or intensity of a single extreme weather event changed because of greenhouse gas emissions.

For example, they concluded that in the major 2016 wildfire in Fort McMurray, Alta., climate change led to "the increased likelihood of extreme wildfire risk and the length of fire seasons."

The 100-year-flood

The two consecutive St. John River floods in 2018 and 2019 have been called, often with astonishment, two "100-year-floods" as if climate change has thrown all our statistical models out of whack.

That's because this is not a well-understood concept.

A "100-year-flood" is simply a flood that has a one in 100 chance of happening in any given year, based on historical data. But they can happen more often.

"A one per cent chance last year is still one per cent this year," said climate researcher Louise Comeau in a recent tweet.

A moving target

Bonsal said the phrase has "always bothered me a little bit. 'One in a hundred years' gives a perception that we're good for another 100 years, but really it can happen any year."

The 100-year flood is also a moving target.

El-Jabi said that what constitutes such a flood is constantly evolving. Once data from 2018 and 2019 are added, the definition of a 100-year flood will shift.

A flood with only a one-in-100 chance of happening will be a bigger flood. Meanwhile, a flood as big as this year's "may be a one-in-50 flood, or a one-in-10 flood," Bonsal said.

Costly consequences

These trends are already proving costly. Last year's flooding cost the New Brunswick government $74 million and counting.

Federal Public Safety Minister Ralph Goodale said recently thatOttawa spent more on disaster relief in the last six years than it did in the 40 years before that.

Flood claims paid out by insurance companies in New Brunswick grew from $59 million in 1996 to $144.3 million in 2015, according to the Insurance Bureau of Canada.

To put that 2015 figure in context, it's larger than the average annual flood payout for all of Canada between 1990 and the early 2000s.

"That gives you an idea of how quickly this has escalated, and why insurers have been saying climate change is a real and present danger," Stewart said.

It's not too late

Another startling element of the recent federal report is that while climate change would be difficult to reverse, it's not too late to avoid worst-case scenarios.

"The rate and magnitude of climate change under high versus low emission scenarios project two very different futures for Canada," the federal report says.

For example, precipitation in Atlantic Canada will increase by 12 per cent by the year 2100 under the "high-emission scenario," a model that Bosnal calls "business as usual" continued growth in greenhouse gas emissions.

But in a low-emission scenario in which Canada and the rest of the world agree to emissions reductions called for in the Paris agreement, precipitation will be only 4.7 per cent higher.

"Future warming is unavoidable," Bonsal said."We will have to be prepared for that warming. We will have to adapt to certain events and impacts associate with that warming.

"But as we go farther into the future, we do have some choices. If we can mitigate greenhouse gas scenarios, we can certainly reduce the impacts."

Better prepared

With this year's floods, the talk has turned to how to prepare for more frequent events.

The Insurance Bureau of Canada now aims to make data from its private climate forecasting available to the public.

"We've been having increasing conversations about how to get the data that these models provide into the hands of the public," Stewart said.

One idea is a searchable federal "flood portal" that would provide "a window into risk for homeowners."

Whether there's a third straight big flood in 2020 or not, Stewart said, "we as a society need to figure out a way to adapt, to lower our risk and to move people out of harm's way when necessary."

Bonsal said Canadians should take a closer look at the report he worked on.

"We shouldn't be surprised in the future," he said. "These events that we have not seen in the past can certainly come in the future. So we should certainly be prepared for surprises."