VANCOUVER — When torrential rains swept away an entire shopping complex in the Saguenay-Lac-Saint-Jean region of Quebec in 1996, the provincial government called the disaster “an act of God.”
And it was Mother Nature who bore the brunt of southern Ontarians’ fury when damage costs soared to $500 million after severe thunderstorms on a single day in August 2005 washed out roads, golf courses and homes.
But a new study by Environment Canada scientists suggests we may have only ourselves to blame.
The study, to be published today in the journal Nature, links global warming brought on by human activity to some of the most extreme rain-driven natural disasters of the last half of the 20th century.
“If these events of this particular size become more frequent, then we’re going to have to pay for damage more often,” said study co-author Francis Zwiers, who worked on the project for 18 months.
“Once every 10 years rather than once every 20 years, for example.”
Using statistical analysis and climate models from around the world, the researchers charted the largest 24-hour rainfall events that occurred in various locations in each year from 1951 to 1999.
Throughout North America, most of Europe and the areas of Asia where they had data, they found the biggest and wettest rain showers, on average, were steadily getting increasingly torrential.
While it didn’t mean the total accumulation of rain was necessarily greater over an entire year, the researchers saw more water vapour collect in the atmosphere in single instances — more rain.
“A warmer atmosphere is one that’s able to hold more water vapour,” said Zwiers, now the director of the University of Victoria’s Pacific Climate Impact Consortium.
“What we’re seeing is not consistent with things like El Nino, it’s more consistent with something that’s acting globally, and the thing that’s acting globally is the effects of global warming.”
The study found the common element to the growing intensity of precipitation was the rising rate of carbon emissions pouring into the skies as a result of fossil fuel use and clear-cutting over the 20th century, Zwiers said.
The results can’t describe exactly to what extent humans are responsible for the heavy rains, but they are useful for predicting future weather events, he added.
“This is really dependent upon how economies develop and whether or not countries come to an agreement on curbing greenhouse gas emissions, (but) if you run the climate models into the future they show further intensification of precipitation.”
Environmental groups have previously asserted a link between changing rain patterns and global warming, but the study authors said their findings are among the first to mathematically explain the science behind the claim.