This text is taken from the Courrier de la Planète. Click here to subscribe.
Quebec is experiencing its worst forest fires in at least 50 years. On Tuesday, nearly 750,000 hectares had been affected by the flames south of 51e parallel. Since 1972 – the year from which we have precise data – never more than 400,000 hectares had burned in one season.
This sad peak is part of a trend in which fires have doubled their grip on the Canadian boreal forest over the past sixty years. There is only “very, very, very little doubt” that this development is linked to climate change, underlines Victor Danneyrolles, professor of forest ecology at the University of Quebec at Chicoutimi (UQAC).
In the boreal forest, fires are a highly variable phenomenon. From year to year, extreme events coexist with dead calm. If we go back a little further in time, we necessarily find seasons when the air in Quebec smelled even more of the burning than last week.
The year 1923 appears in the annals. The Quebec government reported 1.2 million hectares burned. An estimate that may be imperfect, but that gives an idea of the extent of the damage. “The bush is still on fire”, we read in The duty July 19 of that year. In Quebec, “a thick smoke obscured the firmament”.
At that time, the fight against the flames was only rudimentary. “What makes the situation even more serious is that the telegraph lines are partly destroyed and that in many cases it is not known which way to direct the small number of men who have been managed with great difficulty. to bring together”, specifies The duty of July 21, 1923.
However, what about the major trends of previous centuries? Mr. Danneyrolles and his colleagues answered this question using tree rings. They published their results in November last year in the journal International Journal of Wildland Fire.
In a natural (uncut) forest, tree growth lines can be used to estimate when the last fire was. If the trunks that stand are old, it’s been a long time since the flames went through there.
The researchers therefore compiled 16 studies carried out using this method of dating fires. The territory examined stretches from Alaska to Quebec, and the period covered goes back to 1700. By assembling all this data, the scientists found that the boreal forests burned “much more” before the XXe century.
“It’s clear that it was burning much more before,” confirms Mr. Danneyrolles. From two to ten times more, he says in an interview to give an order of magnitude. Then, there is a “particularly strong downward trend” between 1900 and 1950. The “synchronicity” of the decline at most sites suggests that “broad spatial patterns of atmospheric conditions” are involved, write the scientists.
So what happened? The main hypothesis of the Quebec team is based on the “Little Ice Age”, which was then ending. In North America, this period, which began in the fourteenthe century, was not only colder, but probably drier as well.
“Although the average annual temperature and the winters could be much colder than today, we had very dry conditions. Summers could be hot and dry, at least periodically, and therefore conducive to fires, ”explains Mr. Danneyrolles, who is now trying to confirm this hypothesis.
Certainly, the XXe century was a kind of “abnormality” during which Canadian forests burned less, summarizes the professor at UQAC. “The worrying side is that we have become accustomed to forests that burn little,” he says. Our forestry and infrastructure are not designed to deal with many forest fires.
“Now that the fires in the boreal forest are increasing sharply, it’s as if we had a lag in adaptation,” he says. It is therefore far from good news to learn that it was burning more before. »