Climate change could cause lightning to become more common in Canada, and with drought concerns, that could also mean more dry lightning and forest fires.
Heat is a factor in lightning, but how could rising global temperatures affect the frequency of lightning in Alberta?
Temperatures rose dramatically last year: experts say the average global temperature was 1.48°C higher than in the pre-industrial era.
According to a 2014 study published in ScienceLightning strikes are estimated to increase by about 12 percent for every degree increase in average global temperature.
The study analyzed lightning frequency in the Great Plains of the United States, east of the Rocky Mountains, where lightning frequency was already high.
Co-author David Romps says two factors influence the intensity of lightning in a given region: precipitation and the amount of energy stored in the atmosphere, also called convective available potential energy (CAPE).
On a warm day, hot air rises, creating an updraft. When it collides with cooler air higher in the sky, a cumulonimbus — or thunderstorm — can form.
CAPE measures the strength of this updraft and the overall instability of the atmosphere. The higher the instability, the greater the chance of a storm arriving.
Romps’ team used climate models to determine how much CAPE will be in the atmosphere in the coming years.
“When we look at these models as they come out of the century toward 2100, we see that CAPE … increases quite dramatically,” said Romps, a professor in the department of Earth and planetary sciences at the University of California, Berkeley.
“This CAPE growth is driving our expectations that we will see lightning growth.”
Could forest fires become more frequent?
That suggests Alberta — a region that already experiences thunderstorms — could see more lightning as temperatures rise.
Experts say the recent fire that swept through Jasper, Alta., was likely caused by lightning. So could what happened there become a more common occurrence?
Parks Canada does not track lightning in Jasper National Park. However, according to Environment and Climate Change Canada, the town of Hinton, just east of the park gate, recorded an average of 40.2 lightning days per year from 1999 to 2018.
This is the second highest number of lightning days in the province during this period.
Edson, Alberta, a town about 85 kilometres east of Hinton, had the highest average number of lightning days: 46.9 per year.
Lightning strikes in dry, hot conditions
Although thunderstorms are typically associated with rain, snow, and strong winds, they can sometimes occur during hot, dry conditions — a phenomenon known as dry lightning.
“Dry lightning is basically regular cloud-to-ground lightning… the difference is that it occurs with little or no rainfall on the ground,” said Dmitry Kalashnikov, a professor of environmental studies at Washington State University.
A 2023 study published in Development of Earth and space sciencesco-authored by Kalashnikov, looked at the conditions that cause dry lightning to occur.
Kalashnikov was inspired to study dry lightning after California’s particularly bad wildfire season in 2020, which was a record year for the amount of land burned by wildfires in the state. He says California saw 12,000 lightning strikes over the course of several days, igniting several wildfires.
“The fires covered nearly a million hectares of land, which was a really big event,” Kalashnikov said. “People died… many buildings burned down.”
We don’t know if the giant Jasper fire was started by dry lightning, but Kalashnikov thinks it’s likely.
One of the factors indicating the occurrence of dry lightning is the amount of precipitation in the atmosphere, which depends on air humidity and rainfall in a given region.
“After long periods of dry weather, the lower layers of the atmosphere will become drier,” Kalashnikov said.
“This could actually create a feedback situation where the lower atmosphere also becomes drier, simply because there is not enough moisture to transpire from vegetation or evaporate from any surface water sources.”
A 2023 study found that dry lightning strikes when rainfall is less than 2.5 mm.
The Jasper area was in the midst of a heat wave when the wildfires broke out. Less than a millimeter of rain fell in Jasper during the first three weeks of July, according to Environment Canada.
The data shows that the average July receives 52 mm of rainfall.
Does dry lightning pose a greater risk?
As with wet thunderstorms, dry lightning requires instability in the mid-troposphere—between three and six kilometers above the ground.
As dry air from the lower troposphere rises, it reaches the middle troposphere, which is moist and cool, and it receives air from the Pacific Ocean or from locations farther south, such as Arizona or Mexico.
“If there is a large vertical temperature gradient, where warmer conditions are below and much colder conditions are above, the air will want to rise faster,” Kalashnikov said.
“The faster the air rises, the more moisture it can strip from the air particles, and that will cause storms to form faster and faster.” [they] They will actually grow larger and produce more lightning.”
Like wet lightning, dry lightning can cause fires. But does it pose a greater risk?
In his study, Kalashnikov claims that half of the California wildfires in 2020 were caused by dry lightning, further underlining the risk this phenomenon can pose.
New study in Canadian Journal of Forest Research examined Alberta’s 2023 wildfire season, the worst on record. The study found that lightning sparked 13 wildfires in May alone. Typically, Alberta will see one lightning-sparked fire in May.
Kalashnikov says that to understand this threat, you need to examine the forest floor and see how dry conditions are.
In Jasper’s case, given the limited rainfall and the surrounding forests containing beetle-infested trees, a lightning strike could have easily ignited the powder-dry trees.
“When it comes to the risk of forest fires, especially in places like the western parts of the United States and western Canada, dry lightning is certainly more dangerous than any other water storms,” Kalashnikov said.
