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A major hail storm damaged homes and flooded streets in Calgary, in June, 2020.Jeff McIntosh/The Canadian Press

The storm that changed the way Alberta deals with hail happened on Labour Day, 1991.

It lasted about 30 minutes and pelted Calgary with hailstones as big as tennis balls. Hail smashed windows, killed birds and split open trees. In the city, 15 manhole covers blew off and 28 catch basins needed to be unplugged, according to Public Safety Canada. It was, at the time, the most expensive natural disaster in Canadian history. And the insurance industry had to pay out what was then a record amount of money to cover claims.

This is when insurance companies, facing a future where population growth and climate change would make such catastrophes more severe and more expensive, decided to explore ways to control the weather in Alberta. Their goal was to minimize future claims from hail damage in the stretch between Calgary and Red Deer, which is Canada’s hail hot spot, a bull’s eye for Prairie storms.

A consortium of insurance companies, known as the Alberta Severe Weather Management Society (ASWMS), now pays roughly $5-million a year to seed clouds with silver iodide, in hopes of protecting urban communities. While the project’s proponents say it curbs hail damage, critics argue it does nothing to address climate change itself.

Cloud seeding used to suppress hail

Alberta’s hail suppression project uses planes to distribute silver iodide into storm clouds as a way of mitigating property damage

in communities between Red Deer and Calgary.

Without cloud seeding,

ice particles lifted by

updrafts grow in size

Silver iodide flares

are released from

above cloud base

Hail embryos*

form naturally

Ice particles created

by cloud seeding

travel on a lower

trajectory, inhibiting

their growth

Hail embryos*

form only when

cloud is seeded

Silver iodide

released in

updrafts below

cloud base

Rain

Hail and rain

*Ice particles that grow to become hailstones.

the globe and mail, Source: Alberta Severe

Weather Management Society

Cloud seeding used to suppress hail

Alberta’s hail suppression project uses planes to distribute silver iodide into storm clouds as a way of mitigating property damage

in communities between Red Deer and Calgary.

Without cloud seeding,

ice particles lifted by

updrafts grow in size

Silver iodide flares

are released from

above cloud base

Hail embryos*

form naturally

Ice particles created

by cloud seeding

travel on a lower

trajectory, inhibiting

their growth

Hail embryos*

form only when

cloud is seeded

Silver iodide

released in

updrafts below

cloud base

Rain

Hail and rain

*Ice particles that grow to become hailstones.

the globe and mail, Source: Alberta Severe

Weather Management Society

Cloud seeding used to suppress hail

Alberta’s hail suppression project uses planes to distribute silver iodide into storm clouds

as a way of mitigating property damage in communities between Red Deer and Calgary.

Silver iodide flares

are released from

above cloud base

Without cloud seeding,

ice particles lifted by

updrafts grow in size

Hail embryos*

form naturally

Ice particles created

by cloud seeding

travel on a lower

trajectory, inhibiting

their growth

Hail embryos*

form only when

cloud is seeded

Silver iodide

released in

updrafts below

cloud base

Rain

Hail and rain

*Ice particles that grow to become hailstones.

the globe and mail, Source: Alberta Severe Weather Management Society

The hail suppression project uses five aircraft, based in Calgary and Red Deer, to patrol and seed clouds as thunderstorms approach. Despite wobbly evidence for the program’s efficacy, the insurance industry has been funding it since 1996, highlighting the risk underwriters assign to the potential for catastrophic storms.

“For the $5-million it costs the industry each year to fund this, a very modest 1-per-cent reduction of the hail event pays for itself,” said Todd Klapak, an ASWMS board member.

After the 1991 storm in Calgary, residents filed 62,000 insurance claims for $237-million worth of property damage and another 54,000 claims for $105-million in vehicle damage, according to Public Safety Canada and the Insurance Bureau of Canada (IBC). This translates to $567-million worth of claims in 2020 dollars. The payment record stood until the insurance industry doled out $2-billion, in 2020 dollars, for claims after the 1998 ice storm in Southern Quebec.

Alberta’s government began researching whether it could use cloud seeding to mitigate hail damage to crops back in 1956. The province never deployed the strategy and nixed funding for the research in 1985. While the 1991 storm revived interest in reducing hail damage, it also shifted the focus to protecting houses and cars in urban communities, rather than wheat and barley fields in sparsely populated areas.

The ASWMS contracts out forecasting and seeding to Weather Modification International, a company based in North Dakota that started flying missions in Alberta in 1996. The Alberta project employed 11 full-time pilots and four meteorologists in 2021.

Hail forms when small ice particles linger in thunderstorm updrafts within regions of supercooled cloud water. The supercooled water freezes to the ice particles, increasing their size.

The silver iodide particles used to seed Alberta’s clouds act as artificial ice nuclei. These planted ice crystals then compete with natural ice particles for the supercooled water in the cloud, decreasing the potential size of each hailstone.

The province’s hail season runs between June 1 and Sept. 15. To protect towns and cities, clouds must be seeded 20 to 30 minutes before storm cells move over the target zones.

The Alberta project’s planes seed the tops of clouds by shooting small pyrotechnics known as ejectable flares, which each contain 20 grams of the seeding agent, into the updrafts of developing supercooled cloud towers. Each flare burns for about 37 seconds and falls about 800 metres. Cloud bases are also seeded when there are updrafts, using 150-gram flares that burn in place and take four minutes to fizzle out.

The hail suppression project seeds an average of 86 storms a hail season, according to program director Terry Krauss. In the 2022 season, the team conducted 80 seeding flights in 63 storms, he said. It seeded on 27 days.

The previous year, the team conducted only 51 seeding flights in 35 storms, according to its annual operations report. The smaller amount of storm activity could have been related to smoke from wildfires in and around the province, which can prevent heat and moisture from rising in the atmosphere to produce the types of clouds that result in thunderstorms and other severe weather. There were 25 days with hail in the project area, 12 of them with hail the size of walnuts.

Mr. Krauss said recorded radar data serves as evidence the system works. “We absolutely show reductions in the intensity” of storms after seeding, he said. “However, Mother Nature can provide some unusual situations.”

Nature trumped science on June 13, 2020, when a hailstorm hammered northeast Calgary. It resulted in about 70,000 insurance claims and $1.3-billion in insured damages, according to the IBC. The hailstorm now ranks as the costliest in Canadian history, and the fourth costliest natural disaster, the insurance bureau said.

Mr. Krauss’s team had seeded the clouds as the storm approached Calgary, but as the weather system intensified it sucked in a nearby rain shower. This blocked the aircrafts’ access to the storm’s key region, a 2020 operations report said. The scientists on the project hypothesized that the rain may have bonded to the ice particles in the thunderclouds, producing larger hailstones.

There were four seeding flights and three seeded storms that day, the report said. One plane was hit by lightning, and a flare failed on another. Project leaders believe the seeding mitigated damage in Airdrie, Alta., and even in hard-hit Calgary.

“The Chief Meteorologist notes the unique challenges of this storm created the most dynamic, unpredictable and stressful day of seeding he has encountered in his 18 years of hail suppression operations,” the report said.

Mr. Krauss said there is no evidence hail suppression in one area adversely affects another. A 1985 study of North Dakota’s hail-suppression program found seeded clouds produce 5 per cent to 10 per cent more rainfall than unseeded clouds.

The industry has also dismissed concerns over releasing silver iodide into the atmosphere. Mr. Klapak compared it to pouring a teaspoon of salt over Niagara Falls every hour. “There’s more silver in a cup of tea if you stir it with a silver spoon,” he said. The project reports to Environment and Climate Change Canada.

Robin Cox, a professor at Royal Roads University who specializes in disaster management and climate adaptation, said the overall number of hailstorms is expected to decrease in North America. But, she added, the average size of hailstones is expected to grow, because climate change means more moisture in the air. Disaster mitigation techniques, such as better warning systems or cloud seeding programs, are not the solution, she said.

“That doesn’t affect the causes, because the causes are with greenhouse gas emissions and global warming. We are not globally, or in Canada, reducing our emissions rapidly enough and extensively enough.” Decades worth of future climate change, she said, is already locked in by past emissions.

For the insurance industry, this is reason enough to continue to seed thunderclouds over cities such as Calgary and Red Deer.

“If we can do something that helps reduce the damage, or even prevents the damage from happening, I think that is a much better outcome for Albertans than the insurance industry just simply continuing to increase your rates,” Mr. Klapak said.