Floods in Canada: On the Rise

This blog is the first of a 3-part series on flooding in Canada.


It’s springtime in Canada. For many, spring brings a sense of relief that the cold, short days are behind us and gratitude for the warm sun on our skin and the sweet fragrance of blossoming trees. However, this contentment may also be marred with ambivalence: worry that the wet days of spring may precipitate flooding. 

And flooding it is. It’s only early May and already there’s flooding in the east and flooding in the west.

Canadians are starting to get used to news stories about springtime flooding. Although flooding has and will always happen--it is a natural part of the water cycle, and it’s how the physical characteristics of rivers and streams are themselves formed--the frequency and intensity of floods are becoming more prolific.

Major flood events have been steadily increasing over the past century. According to the Canadian Disaster Database, the number of floods in Canada have been increasing every decade for the past century.

 

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Although the database has only logged information up until 2016, this decade (2010-2020) is well on track to yet again be the worst decade for flooding.

Not only have instances of floods been on the increase, but so too have the severity of floods. The five most destructive floods in Canadian history have all occurred since 2010. In order of severity, these are: 

  1. The 2013 flood in Southern Alberta, when a rain-on-snow event caused the Bow, Elbow, Red Deer, Sheep, Little Bow and South Saskatchewan rivers to swell well over their banks, forcing 100,000 people to evacuate from their homes. Damages totalled an estimated $2.72 billion.
  2. The 2014 flood in Southern Manitoba, when the Assiniboine, Qu’Appelle and Souris Rivers reached record flows after heavy rains. Damages totalled an estimated $1.16 billion.
  3. The 2010 flood in Southern Alberta and Saskatchewan, when record rainfall made the South Saskatchewan River and surrounding tributaries swell, causing evacuations on the Blood Tribe reserve and in Medicine Hat, AB. Damages totalled an estimated $1.03 billion.
  4. The 2013 flood in Toronto, ON when an intense storm dropped 126mm of rain in just three hours, causing flash flooding in the Don River Valley and other areas of the city. Damages totalled an estimated $940 million.
  5. The 2011 flooding in Manitoba, which affected 15 communities along the Assiniboine, Roseau, and Red Rivers after wet spring weather caused these rivers to breach their banks. 2500 people were forced to evacuate. Damages were estimated at just under $600 million.

 

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Of course, the increasing destructiveness of floods is correlated to growing populations and a greater number of people living in floodplains. So, part of the increase in destructive floods is because there are more things to damage close to flooding water bodies.

But, increasing evidence points to very large floods--floods that infrastructure are not built to withstand--are becoming more “normal.” For example, the storm in Toronto that lead to flashi flooding in 2013 was over a 1 in 100 year rain event. The 2011 flood in Manitoba was “unprecedented” in terms of flows recorded in the Assiniboine and its tributaries, and the 2014 flood was even bigger than that one. The recent (and, in some places, ongoing) flood in southern New Brunswick brought river levels to record heights in some areas.

 

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It’s early in the year, but across the country we’ve already had our fair share of incidents: an ice jam on the Grand River caused severe flooding in southern Ontario in February. Melting of unusually large snowpacks in B.C.’s southern interior have resulted in evacuation notices in some communities while others are on flood watch wondering if they will be next. And of course, the devastating floods in New Brunswick. 

In most of Canada’s watersheds, streams and rivers reach their peak flows in late May and early June, when snowmelt is at its height. That means there is still 3-4 weeks to go until streamflows peak in most watersheds. That means that the worst may not be over.

As I write this, I occasionally glance out my window to the stream across the street. I live in Kelowna, B.C. right across from Mill Creek-- a highly urbanized stream that flows through the city from east to west. The stream is rushing wildly by. Although it hasn’t yet reached the top of the channel walls in my neighbourhood, a bit upstream it has flooded out parts of the fields surrounding our community recreation center. In anticipation for the worst, the City has issued a state of emergency.

 

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Last year, there was extensive flooding along the creek that caught our local and provincial governments off guard. An intense thunderstorm brought significant rainfall, generating lots of runoff from the rain itself and from the snowmelt that the storm precipitated. Within 24 hours, whole swathes of land around the creek were inundated. Water levels continued to rise over the next couple days.

After the streams were done flooding, it was the lake that flooded. By early June, it was about one meter higher than full pool. Flooded beaches and impaired water quality kept me and many others away from our beloved lakes--a great reprieve from the 30°C+ weather and powerful sun of the Okanagan summer.

 

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Last year, when I was helping neighbours with sandbags, many shared incredulous observations. “I’ve been living here for 40 years and have never seen anything like this,” one man said.

It’s now happened two years in a row.

I know that flooding has happened in the Okanagan for as long as the Okanagan has been a valley (i.e. not a glacial lake--it was definitely flooded then). However, years ago we built flood infrastructure to stop floods from happening (and then built in floodplains). That infrastructure itself brought many ecological issues--but it did hold back water. However, the infrastructure that was built for normal storms in the 1950s and 1960s doesn’t seem to be holding up anymore.

The Okanagan is not a unique case in this regard. Many climate scientists are suggesting that large scale flooding is the “new normal” in an era of climate change.

 

Our next piece in the series will examine causes of extreme flooding, including climate change and land-use change. 


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