Albertans can expect major floods as often as every five years thanks to climate change, according to Gerhard Reuter, a meteorologist and professor at the University of Alberta.
The last three big Alberta floods were in 2013, 2005, and 1996, and followed in the wake of “giant rainstorms,” which Reuter classifies as rain events of more than 200 millimetres. In the last 50 years, these giant rainstorms happened every seven years on average, typically in June because of “cold-core lows” — low-pressure systems that strengthen in height in accordance with the thermal wind relationship.
“The significance of this is that the flow goes in a circle and stays stationary over a point,” said Reuter.
To get them moving you need wind, and that’s where climate change comes in, he said. In the last few years, the wind shear — the way wind speed varies with height — has been reduced, with winds at higher altitudes becoming weaker.
That means intense storms that linger over one area and pummel it with heavy rain will be more common, said Reuter.
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The silver lining in these dark storm clouds is that flood prediction models are now able to track weather patterns about a week before a major weather event occurs.
Unfortunately, Reuter said, these warning signs weren’t heeded last year.
“I was tearing out my hair in frustration. They were about to have major flooding, and the radio stations were discussing the highs and whether it would be plus 24 or plus 23.”
The time has come to make this sort of weather data available to the public, including maps or charts that explain the amount of precipitation in a given week, he said.
“Then let the people or the farmers decide what they can make out of it,” he said.
That would have made a major difference for many of last year’s flood victims, he added.
“I sent emails to my friends in Calgary telling them to pack their stuff and move stuff out of their basements,” said Reuter. “Some people got two hours’ notice and they had to leave. It was a disaster that was completely human made because they were not prepared.”