Multi-year droughts are becoming hotter, lasting longer and causing more damage: study
Most severe multi-year droughts in recent decades include ones in Australia and the western U.S.
Droughts that stretch on for years at a time are becoming longer and more devastating for ecosystems across the globe, according to a new study.
And in the wake of 2024 being declared the hottest year on record, it's raising questions about how prepared Canada is for what's to come.
When an individual drought event has a huge impact on the environment or communities, it garners a lot of attention. But many droughts occur in regions with a low enough human population to go unreported, or in tropical or mountainous regions where the impacts aren't immediately detrimental or obvious, making it hard to get an accurate picture of the occurrence of drought.
For this study, published in the peer-reviewed journal Science, researchers mapped out the global distribution of more than 13,000 multi-year droughts, which occurred from 1980 to 2018, to get that big-picture look.
They found that multi-year droughts are becoming hotter, longer and more severe, and have occurred on nearly every continent.
The land affected by multi-year droughts is increasing by nearly 50,000 square kilometres globally per year, according to the study.
"Which is more than the area of Switzerland," Dirk Karger, senior researcher at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and senior author of the study, told CBC News.
Researchers measured drought severity by looking at the balance of precipitation in a region versus how much water was lost to evaporation. They also used satellite images to measure changes in vegetation greenness, and found that grasslands are the most affected by drought conditions.
Among the most severe events in recent decades were multi-year droughts in Mongolia, southeastern Australia and the western United States.
'Tipping points'
Several of the multi-year droughts that researchers identified were ones that had gone overlooked in regions of the Andes and the Congo and Amazon rainforests.
Tracking these matters even if the individual impacts aren't immediately obvious or detrimental, Karger said, because multi-year droughts can lead to "tipping points" where the quality of soil and vegetation in an area has been so damaged that recovery is impossible, turning forests into savannahs and savannahs into deserts.
In December, a United Nations report found that more than 75 per cent of land on Earth experienced drier conditions in the three decades leading up to 2020, compared to the three previous decades.
The increase in severity of multi-year droughts is "strongly driven by climate change," Karger said.
It's a vicious cycle — forests deprived of water and unable to grow are also taking in less CO2 from the atmosphere.
"And then we actually have forests, instead of being a carbon sink, becoming a carbon source," Karger said.
Lasting adaptation needed
Canada is far from exempt from this problem.
"We've always assumed we had plentiful water, but recent years in British Columbia, Saskatchewan and even parts of the North have shown that we don't have secure reliable water supplies all the time," John Pomeroy, professor and UNESCO chair in mountain water sustainability at the University of Saskatchewan, told CBC News.
We've also been experiencing "snow droughts," he said, which occur in Canada's northern regions when a low snow supply results in a low yield of meltwater in the spring. And with many of Canada's glaciers set to vanish in the "next 10 to 20 years," Pomeroy says we're going to lose the "drought proofing" that they provided during the hottest and driest years, when glacier melt gives a boost to rivers and streams.
Canada needs to adapt to a world with worse droughts, he added, building more reservoirs, conserving more water by making crop irrigation more efficient and working on forest management to fight the wildfires that increase whenever droughts occur.
Inter-province agreements surrounding the flow of water may also need to be revisited to make plans for the increasing drought events.
A severe multi-year drought can have huge ripple effects across life and industry.
One of Canada's worst droughts, which spanned 1999-2005, caused shipping to be restricted on the Great Lakes, a loss of 41,000 jobs in the Prairies and an increase in suicides among farmers, Pomeroy said, as well as "a $6 billion economic hit to Canada."
"We need to be prepared and not responding as an emergency every time one hits," Pomeroy said.
"You can kind of sleepwalk into a situation like this, when it gets steadily a little worse every year, and that's sort of the way it's been for Canada."
ABOUT THE AUTHOR
