Climate making disasters like B.C. rain more frequent and more intense: scientists

Climate scientists have been warning of catastrophic weather for years now, but nobody’s happy the predicted floods and slides crippling British Columbia this week have come to pass.

“It’s not really an I-told-you-so moment, but seeing it firsthand really does bring home the effects of climate change,” said Nathan Gillett of Environment Canada’s Centre for Climate Modelling and Analysis in Victoria.

“Even though I study the climate, it is still quite shocking.”

Rainfall in buckets has set more than 20 records across the province over the last few days, including 252 millimetres over three days in Hope, B.C. Highways were closed, communities evacuated and more than 100,000 people were without power at some point.

Get used to it, said Francis Zwiers of the Pacific Climate Impacts Consortium at the University of Victoria. More extreme events, more often, have been a fixture of climate models almost from their beginning.

“Precipitation extremes are probably going to become more intense as the climate warms,” he said Tuesday. “What we’re seeing is not inconsistent with what the climate models are saying.”

The B.C. government itself acknowledged the risks two years ago. A 2019 Strategic Climate Risk Assessment said severe river flooding, extreme precipitation and landslides were all “medium” risks.

That study, a first in Canada, is now being replicated in other provinces, said Joanna Wolf, director of B.C.’s Climate Action Secretariat. 

“Risk assessment is being understood as one of the fundamental exercises you can take,” she said. 

Warming temperatures don’t necessarily cause destructive weather. They exaggerate natural variability — what would have been a heavy rain becomes Biblical and once-a-decade storms return every third year.

“We’re affecting frequency and intensity in many kinds of events,” said Zwiers.  

There’s even a formula, he said. For every degree of warming, the atmosphere can hold seven per cent more water. 

Scientists caution that climate change can’t be blamed for everything. 

Weather cycles such as the back-and-forth between El Niño and La Nina years have a big impact. So do factors such as landscape management — for example, a clearcut slope has less ability to hold water than one that retains its trees. 

“There’s a role for human influence but there’s a lot of natural influence as well,” said Zwiers. 

But the evidence for links between extreme weather and climate are growing clearer all the time through an increasingly prominent branch of climatology called attribution science. Last summer, researchers concluded the heat dome that brought unprecedented temperatures to B.C. would have been all but impossible without climate change. 

It’s easier to pin heat waves on climate change than heavy rain, said Gillett. Still, he expects the connection to be drawn in the case of B.C.’s recent travails.

“No one has yet had time to do the studies. But we can say for this region, increases in rain extremes are projected due to the effects of climate change.”

Studies affirming what climate modelling has already predicted are a bit of an I-told-you-so exercise, acknowledges Danny Blair of the Prairie Climate Centre in Winnipeg.

“I’m always cautious about saying too much about an event being attributed to climate change. But as they happen more and more often and more and more intensely, there has to come a moment where you realize, yeah, it is having an effect.”

But, he said, they’re worth it if they get public attention for the need to fight climate change. 

“It wakes people up,” said Blair. “That is a moment where you can say climate change is real, climate change is causing damage, climate change is something we need to deal with.

“The big take-away? Let’s do something about it.”

This report by The Canadian Press was first published Nov. 16, 2021.

Bob Weber, The Canadian Press