Icy Winters in Canada’s Past and Future

The most recent major event, the 2013 Toronto Ice Storm, deposited 30 mm of freezing rain onto the city, causing major damage to trees and power lines. Widespread power outages from the storm left more than 1 million people without electricity for nearly three days, tens of thousands for more than a week. Insured losses for the event totaled about CAD 200 million.^2,3

The January 1998 ice storm—discussed in the next section—stands as the most severe ice storm to hit Canada in recent memory due to the thick ice accumulation, the storm's multi-day duration and areal extent, and the population affected.

The Great North American Ice Storm of 1998

From January 4 through January 10, 1998, a devastating ice storm with high levels of precipitation moved across a broad, high-population area, from eastern Ontario to southwestern Quebec, southern New Brunswick, and Nova Scotia (as well as northern New York and parts of New England). The Great North American Ice Storm of 1998 dumped 73 mm of freezing rain on Kingston, 85 mm on Ottawa, and 100 mm on areas south of Montreal over the course of 80 hours, leaving a coating of ice on buildings, power lines, transmission towers, tree branches, vegetation, vehicles, and roads. The storm claimed 28 lives in Canada and 17 in the United States.

As the 1998 storm demonstrated, in addition to the risk of death and injury, ice storms can have a widespread impact on a regional economy from physical damage, as well as from power outages that darken homes and shutter businesses.

Damage, Power Outages, and Disruption

Southeastern Ontario and southern Quebec suffered the most damage and disruption from the 1998 ice storm, primarily from the weight of accumulated ice on trees and on power lines and their supporting structures. Millions of trees were damaged, with broken branches often falling on buildings, vehicles, and power lines, causing additional damage.

According to Statistics Canada, the heavy ice load brought down more than 30,000 wooden utility poles and toppled more than 1,000 transmission towers, of which 130 were major structures.⁴ (See Figure 2.) Approximately 90% of the 4.7 million people affected by the region-wide power outages lost electricity for more than a week, some for as long as a month.⁵  

Significant service outages were experienced in Quebec, where more than 3,000 kilometers of the power distribution network were affected. (See Figure 3.) Major rebuilding of the power distribution network was required in the storm's aftermath.

In Montreal, power outages shut down much of the city's water supply system when pumping and filtration plants lost power, resulting in drinking water shortages for thousands of residents.

At the peak of the crisis, about 16,000 Canadian soldiers were deployed in the most severely affected areas, the largest peacetime deployment of Canadian troops ever. Icy roads—often blocked by fallen tree branches—slowed the pace of recovery.

Losses

The six-day Great North American Ice Storm of 1998 had a catastrophic impact on the Canadian economy, with an estimated CAD 4.5 billion in losses (1998 dollars).⁷  

Insured losses totaled about CAD 1.6 billion in 1998 dollars, the largest insured loss in Canadian history.^{8, 9} More than 660,000 insurance claims were filed in Canada (a figure just short of the number of claims submitted after Hurricane Andrew devastated coastal Florida in 1992). Almost two thirds of the total loss was paid to residential coverages, 30% to commercial, and 10% to automobiles.

More than 2.6 million people (nearly 20% of Canada's labor force) were impeded or prevented from getting to work. The ice storm disrupted many agricultural and business communities for several days, generating huge losses for farmers (especially dairy farmers), the maple syrup industry, and timber companies.

Multiple Modes of Damage

As the 1998 storm demonstrated, freezing rain can cause significant losses through several mechanisms. While both freezing rain and snow produce loads that act on structures, freezing rain tends to adhere to surfaces and leads to ice buildup, which increases the load on structures as well as the surface area exposed to wind. Generally, more winter precipitation accumulates on structures from freezing rain events than snowstorms, increasing the potential for damage and loss.

Accumulated ice also can cause greater damage to trees and power lines than snow. In general, 6 mm of radial ice thickness—typically produced by 12 mm of freezing rain—results in extensive damage to trees, such as limb and trunk breakage and uprooting. The impact of thick, heavy ice increases with high winds, which often accompany winter storms, enhancing the likelihood of damage. As shown in Figure 4, falling limbs and trees can also damage nearby structures and vehicles, as well as bring down power distribution lines.

In extreme events, ice-laden power transmission towers and other support structures can collapse in chain reactions, causing a cascading failure of transmission lines. The resulting power outages can trigger time element losses, including business interruption losses and additional living expenses, because otherwise functional offices buildings or residences might not be habitable for lack of heat or lighting. Outages also can lead to additional content losses due to food spoilage, and the risk of flooding due to burst pipes increases if the heating system operation is interrupted.

To explicitly model building, content, and time element losses resulting from freezing rain, AIR scientists developed an Ice Accumulation Index specifically for the Canadian environment. (See Figure 5.) The index, which is based on the Sperry-Piltz Ice Accumulation Index™,¹⁰ captures the impact of both ice accumulation and wind speed at a given location (since high wind speeds during ice storms can increase damage significantly due to wind loading).

Closing Thoughts

Freezing rain in Canada can be a relentless and costly peril. While the Great North American Ice Storm of 1998 was the most damaging freezing rain event in recent history, companies should prepare for the possibility of greater losses, even though improvements have since been made to the power systems. Furthermore, in any given year, similar loss levels from freezing rain might be reached through the aggregation of losses from multiple smaller events.

Effectively managing the risk of physical, content, and time element losses from freezing rain calls for a probabilistic model based on robust hazard data, a comprehensive view of vulnerability, and accurate exposure data.