Tracking the severity of Quebec floods is a complicated science – Montreal Gazette

Tracking the severity of Quebec floods is a complicated science - Montreal Gazette
Ottawa declares state of emergency as water keeps rising
Were going to see more and more of these extreme weather events more regularly, Justin Trudeau said.

Canadian Forces personnel sandbag a house against the floodwaters Thursday in Laval. Ryan Remiorz / THE CANADIAN PRESS

Environment Canada earlier on Thursday issued a special weather statement warning of “significant rainfall” in the Ottawa area totalling 20-35 millimetres between Friday morning and Saturday morning. This heavy precipitation coupled with the spring snowmelt has the Ottawa River Regulating Committee forecasting peak floods reaching 11 centimetres above 2017 levels in the Britannia/Lac Deschenes area on Sunday.

During his Sunday tour of Île Bigras, a picturesque Laval community in the middle of Rivière des Prairies that’s been flooded twice in the last three years, Premier François Legault said Quebec was going to have to rethink its compensation strategies given the increasing frequency of flooding events caused by climate change.

The municipality issued a plea for help to the provincial and federal governments after assessing new weather and river level forecasts for this coming weekend. Ralph Goodale, federal minister for public safety and emergency protection, confirmed Thursday evening the Government of Canada is sending help, “including support from the Canadian Armed Forces.”

City of Ottawa declares state of emergency as flood levels projected to rise above 2017 peak

“We’re going to see more and more of these extreme weather events more regularly,” Justin Trudeau said.

As Quebecers grapple with another disastrous season that has flooded 1,900 homes so far, only two years after water levels rose to historic levels and flooded out more than 5,000 residences, there is a common perception that the frequency and severity of flooding events has increased significantly over the last decades.

“Anything Ottawa needs to help affected families and support city staff on the ground, the Province of Ontario will be there to support them,” the premier wrote. “My message to Mayor Watson and the people of Ottawa is this: together, we will get through this.”

Backing that perception up with hard figures is difficult, however, due to a lack of historical data and the extreme swings seen in natural variability.

The City of Ottawa has declared a state of emergency as water levels along the Ottawa River are expected to rise above the flood levels in 2017 that were “devastating” to many communities bordering the river, Mayor Jim Watson announced on Thursday afternoon.

For instance, explains Daniel Henstra, a University of Waterloo professor specializing in flood-management policies, and a fellow at the Centre for International Governance Innovation, a so-called “100-year flood” refers to a flood the magnitude of which has a statistical probability of occurring once every 100 years, or, in other words, has a 1 per cent chance of occurring in any given year. Since the probability is the same from year to year, it is possible for a community to experience such a flood in two consecutive years.

The mayor and city staff thanked the more than 1,200 volunteers who have “tirelessly” helped fill sandbags and supported other flood preparation efforts over the past week. They said the city still needs folks to lend a hand in the coming days.

“Due to a lack of available (longitudinal) data, it is practically impossible to know whether the frequency of these ‘100-year floods’ has increased in Canada,” Henstra said. “Although it would seem that way, given the number of events we have been experiencing, we don’t have sufficient, convincing evidence that these events are actually becoming statistically more likely.”

Add to that the fact it’s difficult to separate climate change effects from natural variability. Quebec has experienced several devastating inundations in the past since all rivers flood at some point as part of the natural life cycle of a river, said Pascale Biron, an expert in river dynamics and professor in Concordia University’s department of geography, planning and environment. The Canadian Disaster Database run by Public Safety Canada records that Quebec has suffered several major flooding events over the last decades. They include one in the Saguenay region in 1996 that forced the evacuation of 15,825 residents, and another in 1998 in eastern Ontario and Quebec that evicted 3,757 from their homes. In 1974, major flooding ravaged the Maniwaki region.

While the city has enough sand and sandbags to set up around properties at risk of flooding, it no longer has enough manpower or time to meet residents’ needs in the face of the “worsening forecast,” officials said.

But whether there are more frequent, severe storms now than in decades past is hard to tell, Biron notes, because there are not many gauging stations in Quebec that have long historical records, and the way flood levels are measured has evolved technologically, so it’s not always possible to compare discharge levels from the 1930s with those from the 2000s. At the same time, changing land use from forested zones into urban areas can also have a major effect.

Kanellakos couldn’t say how long the City of Ottawa will be in a state of emergency, which gives the municipality the authority to buy any supplies that are urgently needed without going through the normal tendering processes.

“Unfortunately the science is just not good enough to attribute a particular local extreme weather phenomenon to climate change, particularly in a data-poor country like Canada,” Henstra said.

What scientists have concluded is that most climate change models predict more frequent extreme precipitation events in the future, Henstra noted, which could lead to more river flooding, as well as urban flooding and coastal flooding as sea levels rise.

The centres will be staffed with representatives from Ottawa Public Health, the city’s community and social services department, the Salvation Army and the Canadian Red Cross, according to the city.

“Overall (not just in Quebec), scientists believe that events that were on average occurring once in 20, 50 or 100 years, may occur more frequently in the future because warmer air is able to hold more moisture, so perhaps a 50-year flood will become a 40-year flood in the future,” Biron said.

Ottawa Mayor Jim Watson declared a state of emergency for the city in response to flooding and the rainfall forecast for the coming days. He said the Canadian Armed Forces have also been requested.

“I think what is safe to assume is that the climate will become more unpredictable in the future, so we need to prepare for flood events that we have not seen yet, realizing that the natural variability will always remain, but the amplitude of the changes will likely increase,” Biron said.

The communities most threatened by rising water levels include Cumberland, located east of downtown Ottawa, and Britannia and Constance bays, located west of the downtown core.

The inability to present hard data can be frustrating for researchers who note it makes it more difficult to convince Canadians to pay now in order to prevent catastrophes in the future.

“We will continue to have ample stocks for residents,” he said on Thursday. “More than 200,000 sandbags have been made available as of this morning.”

In its overview of climate change nationally, Natural Resources Canada wrote that national trends in precipitation are difficult to assess largely due to the fact it comes in different states (rain, snow, freezing rain) and differs largely by region.

Watson said it’s too early to tell how much the escalating flood response will cost the municipality, but staff said the city has already started tracking expenses.

“Nevertheless, Canada has, on average, become wetter during the past half century, with mean precipitation across the country increasing by about 12 per cent,” the overview finds.

Volunteer check-in locations can be found on the city’s website. City officials urge residents to steer clear of volunteer and military operations over the weekend.

In Quebec, government ministries base their strategies and actions on studies published by scientists and researchers in the domain, said Louise Quintin, a spokesperson for the province’s ministry of public security. After the 2017 floods, Quebec ordered the creation of costly flood maps for the whole province by the end of 2020, after decades of going without.

“If the flooding is severe, there could be weeks of recovery operations, but our commitment to residents is the city will be there to help,” Kanellakos said.

In Quebec, the combination of science and repeated, heavily publicized flooding events occurring in rapid succession appear to be shifting government attitudes.

The City of Ottawa has declared a state of emergency as river levels continue to rise, threatening to surpass those reached when flooding devastated some neighbourhoods two years ago.

We can no longer do it alone.- Ottawa Mayor Jim WatsonEnvironment Canada has issued a special weather statement predicting up to 35 millimetres of rain by Saturday morning, and river authorities are now forecasting that in some areas, the water could rise up to 11 centimetres above peak levels reached in May 2017.

The municipality hopes to have about 400 members of the military helping out on the ground, with the first troops arriving on Friday morning, city officials said.

Watson said he's also asked for help from the Canadian Armed Forces, and has been told 400 troops will be deployed to key areas.

As for sandbags, the city’s general manager of emergency and protective services, Anthony Di Monte, said sand and empty bags are available across the city.

"We can no longer do it alone," Watson said. "We are now beyond our city's capacity, and that is why we have called in the Armed Forces."

As of 2 p.m. on Thursday afternoon, the city had received a total of 180 service requests from homeowners — about 60 a day — according to senior staff.

City manager Steve Kanellakos said the city felt prepared until the latest forecast from Environment Canada.

"I can say with certainty that the flooding situation has changed almost in the blink of an eye," he said.

“Ottawa has a lot of heart and these volunteers come out over and over again, just as recently as the tornadoes last fall,” Kanellakos said.

"I cannot tell you how long we will be in this state of emergency. If the flooding is severe there could be weeks of recovery operations."

Premier Doug Ford has also pledged the provincial government's support, and will visit the region on Friday.  

While levels on the Rideau River have stabilized, the Ottawa River is expected to rise about half a metre from Constance Bay to east of Cumberland by the weekend, according to South Nation Conservation.

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