Canada is witnessing more thunderstorm impacts than ever before

Gregory Kopp, Western University; David Sills, Western University, and Julian Brimelow, Western University

Residents in eastern Ontario are still recovering after a tornado-producing thunderstorm left a path of destruction over 55 kilometres long and up to 1,400 metres wide in July.

Such thunderstorms, and the damage they leave behind, can have deep and far-reaching impacts on society and the economy, and they are only increasing.

In Canada, the new normal for yearly insured catastrophic losses has reached $2 billion — a significant increase from the $422 million per year between 1983 and 2008 — and a significant chunk of that is from thunderstorm-related severe and extreme weather.

We at the Northern Tornadoes Project and the recently launched offshoot — The Northern Hail Project — are often asked whether these severe and extreme weather events are on the rise, and if this has anything to do with manmade climate change? The simple answer is: it’s complicated.

The difference between severe and extreme

Severe thunderstorms occur in Canada every year, bringing with them large hail, damaging downburst winds, intense rainfall and tornadoes. More rare and of even greater concern are extreme weather events — with their size, intensity or even time of year well beyond what is typically expected based on past observations.

Long, thin tornado from thunderstorm base to ground
Prairie tornado in D’Arcy, Sask. on June 15, 2021. (David Sills), Author provided

Extreme weather conditions include tornadoes causing damage rated EF3-EF5 and significant hail of over five centimetres in diameter. Extreme weather can also arise when large hail accompanies downburst winds — increasing the hailstone impact energy — or when a long-lived thunderstorm system results in a derecho, which is a cluster of downbursts (and sometimes embedded tornadoes) resulting in intense damage over hundreds of kilometres.

In September 2018, for example, a tornado outbreak in the National Capital Region caused catastrophic damage resulting in over $300 million in insured losses. It is also the latest in the year that a tornado outbreak with up to EF3 damage has been recorded in Canada.

In June 2020, Calgary experienced Canada’s first billion-dollar hailstorm and fourth costliest natural disaster on record, with insured losses of $1.3 billion. The derecho in May 2022 that mainly affected southern Ontario took 12 lives, with early estimates of insured losses close to $900 million. And that’s just over the last four years.

How can we detect these trends?

Such events and their impacts cannot be adequately assessed and documented using standard operational weather observation platforms such as radar and surface weather stations.

Tornado tracks and hailswaths are inherently narrow and often pass between stations. Radar can capture some of the key meteorology, but not the impacts on the ground.

Comprehensive storm surveys by weather and engineering experts are required to fully assess and document the meteorology and its physical impacts through what we call an “event-based approach”. In fact, we recently added a social science component to such investigations to better capture the impacts on people and communities. The living database that results from these storm surveys can always be updated as new information is discovered.

Map depicting a 2017 tornado outbreak in Québec
A map shows the starting locations and tracks of the 23 tornadoes that occurred during a two-day tornado outbreak in Québec in June 2017. (Lesley Elliott and Liz Sutherland/The Northern Tornadoes Project), Author provided

This approach allowed the Northern Tornadoes Project to uncover one of the largest recorded tornado outbreaks in Canadian history — 23 tornadoes over two days in Québec — and increase the number of tornadoes documented across Canada each year. It has also allowed the new Northern Hail Project to recover and document Canada’s largest hailstone on Aug. 1, 2022.

The greater the length and better the quality of a national database of these events, the more likely it is that any severe and extreme storm trends will be detected.

Some progress has been made

The tornado data for Southern Ontario is of sufficient length and quality to allow us to begin to look for trends. A 2022 study found that the annual number of tornadoes recorded there since 1875 has grown substantially. But that is mainly due to an increase in weak tornadoes — ones that might have gone unreported in the past but now fail to escape the attention of the expanding population with consumer-grade cameras at the ready and access to social media for sharing.

The same study found, however, that tornadoes rated F/EF2+ in southern Ontario occurred gradually later in the year since 1875, now peaking in late summer rather than early summer.

Meanwhile, in the U.S., studies have shown that tornadoes may be occurring in bigger clusters and starting to shift eastward – away from the Great Plains and into more populated areas.

In all cases, clear connections to man-made climate change have not yet been established. It is also yet unknown whether extreme storms are changing in ways that are different from severe storms. But it’s still early and research in this area is growing rapidly.

While storm trends are studied, prepare for increased impacts

Canadians are recording and sharing images and experiences of severe and extreme storms more than ever before, increasing the documentation of these events. As the population continues to grow and spread out, the damage and losses caused by thunderstorms will continue to grow.

Damaged cars are seen next to the remains of houses damaged by a tornado.
Damage from an EF2 tornado in Barrie, Ont. on July 15, 2021. (Northern Tornadoes Project), Author provided

At the same time, we are learning more about changing storm patterns and possible connections to climate change. Continuing to increase the length and quality of our national severe and extreme storm event database is needed to better understand such changes.

In the meantime, developing adaptation strategies to ensure resiliency and to lessen the impact of inevitable damaging storms is becoming increasingly important. Improving upon building codes and other policies to promote more resilient buildings and communities is urgently needed to better protect the lives and property of Canadians.

Gregory Kopp, Professor of Civil Engineering & ImpactWX Chair of Severe Storms Engineering, Western University; David Sills, Executive Director – Northern Tornadoes Project, Western University, and Julian Brimelow, Executive Director Northern Hail Project, Western University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The cheaper we build our buildings, the more they cost after an earthquake, wildfire or tornado

Keith Porter, Western University

A tornado cut a 270-kilometre path through Kentucky in mid-December 2021, killing 80 people, many in their homes or workplaces, and rendering thousands homeless. The incident prompted David Prevatt, a professor of structural engineering at the University of Florida, to write an opinion piece for the Washington Post, reminding Americans that new buildings could be tornado proof, but are not.

We are learning similar truths in Canada. Barrie, Ont., struck by a set of tornadoes on July 15, 2021, is still recovering. So too, are those who survived the fires in Fort McMurray, Alta., in 2016, and in Lytton, B.C., in June 2021. It’s the same story following the floods in British Columbia in November 2021 and the derecho that struck Southwestern Ontario in late May, lifting roofs off some buildings and destroying others.

Engineers, architects and builders can design and construct affordable new buildings that can resist tornadoes, floods and wildfires without making the buildings into bunkers. We could also design earthquake-resilient buildings, but do not.

I am a structural engineer and an expert in performance-based engineering and catastrophe risk management. I believe the only way to make that happen is to require our building code to minimize society’s total cost to own new buildings. We have always been free to make that happen, but have a rare window now to shape that future, as the nation and code developers urgently respond to the climate crisis.

Why don’t we build resilient buildings?

Building-code writers, engineers and others frequently tout the benefits of modern building codes. But new buildings only keep us relatively safe; they’re not disaster proof. Why don’t we build better buildings? Because it would cost a little more.

We build to minimize initial construction costs while maintaining a reasonable degree of safety and avoiding damage where practical, a strategy known as “least-first-cost” construction. We save a small amount on initial construction costs and call the savings “affordability.”

But that kind of affordability is an illusion, like a tantalizingly low sticker price on a flimsy car. Wise car buyers know that the low cost is just the beginning of a series of bills.

In new construction, every dollar saved weaves in $4 or more of future costs to pay for unpredictable catastrophes: severe storms, massive earthquakes and catastrophic wildfires. That future cost is not an if, but a when — or rather a sequence of whens made more frequent and severe by the climate crisis.

In research for the U.S. Federal Emergency Management Agency and others, my colleagues and I applied simple methods to design buildings to be stronger, stiffer, or above the flood plain than the U.S. building code currently requires. (Canada’s National Building Code is similar.) We found that society would initially pay about one per cent more for new construction, but avoid future losses many times greater, minimising society’s long-term ownership cost.

Engineers could have used these ideas long ago. If we had, Canada wouldn’t be losing over $2 billion annually to natural catastrophes, equivalent to the cost of four days of new construction.

Our losses grow nine per cent every year, like a credit card that gets charged more each month than is repaid. But unlike a credit card bill, nature demands an unpredictable, enormous payment any time it wants, from anywhere in the country. No Canadian community is immune.

Graphic showing the rate of increase of disaster losses compared to population growth.
Canada’s annual disaster losses have grown about nine per cent annually, 10 times faster than population growth. Author provided

We can fix the problem

Prime Minister Trudeau has committed to bold, fast action on climate change and its associated disasters, and better building codes can be a part of it. We could install sewer backflow valves in homes and workplaces, use non-combustible siding rather than vinyl in the wildland-urban interface (where the built environment mingles with nature) and install impact-resistant asphalt shingle roofs in hail country. Engineers have long lists of ready-made solutions both for new buildings and the ones we already have.

Building codes created those problems. They aim for safe and maximally affordable construction, and ignore long-term ownership cost. We build cheaply but not efficiently.

Three fatal tornadoes in 15 years convinced city officials in Moore, Okla., that the national building codes weren’t protecting them. So, they enacted an ordinance to make new buildings resistant to all but the most severe tornadoes.

Developers warned that the stricter requirements would drive up home prices and that development would dry up or move outside Moore. Neither thing happened. A few years after the ordinance passed, researchers found no impacts on home prices or development.

Other jurisdictions could do better too, just like Florida did after Hurricane Andrew in 1992. The state leapt ahead of U.S. building codes with its own stricter, more cost-effective code. The Insurance Institute for Business and Home Safety developed a voluntary standard, called “Fortified,” that reduces future losses and more than pays for itself in higher resale value.

Disaster-resilient buildings that also cost less

The climate crisis is forcing major energy-efficiency changes to the building code, offering a rare opportunity to fix our growing disaster liability and minimize long-term ownership cost. The update might include these three steps:

  • Enact a building code objective to minimize society’s total ownership cost of new buildings. The Canadian Commission on Building and Fire Codes could formalize the principle in the National Building Code of Canada.
  • Require code-change requests (proposals people make to the Canadian Commission on Building and Fire Codes for inclusion in the National Building Code) to be accompanied by estimates of added construction costs and benefits in terms of reduced energy use, future repair costs, improved health and life safety outcomes, and other economic effects whose monetary value can be reasonably estimated.
  • Limit the freedom of code committees to reject cost-effective code-change requests.

Such changes will eventually shrink Canada’s disaster credit card balance. While Canada rethinks energy efficiency, it can also tackle the false economy of least-first-cost construction. With slightly greater initial costs, our buildings will be better able to survive disasters and cost less to own in the long run.

With a wiser code, we can have better, safer, more efficient buildings for ourselves, our neighbours, our children and all future Canadians.

Keith Porter, Adjunct research professor, civil and environmental engineering, Western University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Hurricane straps keep roofs on houses and can improve safety during tornadoes

Gregory Kopp, Western University

Many people think of a well-built house as one where the walls are strong enough to hold up the roof so it won’t fall on them. This is reinforced by children’s stories like the Three Little Pigs, where the house made of brick is the strongest when the Big Bad Wolf comes to town.

When a strong tornado passes through a neighbourhood, it results in total chaos. Debris is everywhere. Shingles and siding and bricks are thrown about. Entire roofs are tossed, often landing on neighbouring homes. Walls collapse, cars are rolled and flipped. Insulation is stuck to every surface like a strange snowfall.

On July 15, a tornado struck Barrie, Ont., destroying several homes: Could anything have been done to minimize the damage in Barrie?

Holding on to the roof

In any windstorm, tornadoes included, the roof needs to be secured — this is due to the uplift, the same physics that allows an aircraft to fly. This runs counter to our intuition since we tend to think about roofs collapsing, not flying. The uplift is the main vulnerability of houses. The structure of residential roofs in Canada tend to be strong because they are designed to handle the heavy weight of snow in winter.

For the wind, which acts in the opposite direction as the snow, it is the nails connecting the trusses to the top of the wall that become critical to ensure that the roof stays in place during a severe storm.

The National Building Code of Canada requires three nails — just over three inches long — in each roof-to-wall connection. These toe nails, as they are called, are what hold the roof down in the wind. If this is done properly, the roof structure should be safe until wind speeds reach about 160 kilometres an hour. At such wind speeds, asphalt shingles may blow off but the roof structure will remain intact.

Houses are not designed for tornadoes, although the building code discusses tornadoes. The requirements for fastening the walls to the foundations were developed to deal with tornadoes. These were included in the 1995 release of the National Building Code following tragic deaths in 1984 when cottages were swept into Blue Sea Lake in Québec, along with post-storm observations following a 1985 tornado in Barrie.

It is now known that toe-nailed connections are the weak links in the structure, more likely to fail before the roof sheathing and before the walls pull apart from the foundation. Walls are more likely to collapse when the roof is gone, and the roof itself can become airborne. Both of these are threats to life and safety.

The Northern Tornadoes Project survey in the immediate aftermath of the recent tornado in Barrie indicated that several homes did not meet the building code requirements because of missing toe nails.

This is nothing new.

Similar observations were made in 2009, when tornadoes landed in Vaughan, and in 2014 in Angus.

Unknown speeds

To design for tornadoes, we need to know the wind speeds in tornadoes. These are rarely measured. Rather, tornado wind speeds are assessed through the damage they cause, via the Enhanced Fujita Scale.

The recent Barrie tornado was assessed to have had maximum wind speeds of 210 kilometres an hour based on the damage to a few of the houses. It was a strong tornado. However, if this strong tornado had instead gone through farmers’ fields, missing all buildings and trees, then it would have been assessed as an EF-0 (90-130 km/hr) tornado even though its true strength was greater. Clearly, the use of damage to estimate the tornado wind speeds is challenging, particularly in sparsely populated areas.

As a result, the reported intensity of a tornado — its maximum wind speed — depends on what it hits and, therefore, on the quality of construction. A roof with only a single toe nail would be assessed as EF-1, while properly installed toe nails yield an expected wind speed of about 195 kilometres an hour, which is EF-2.

Put another way, a wood-frame roof is expected to fail in an EF-2 tornado, while improper toe nails would lead to roof failure in an EF-1 tornado. As a result of this uncertainty, quantifying wind speeds in tornadoes is still an active topic of research and development.

Nevertheless, the combination of tornado simulators, wind tunnels that create tornado vortices to define the wind forces on buildings, and full-scale laboratory tests on houses to determine their strength has helped. They’ve provided good estimates of failure-inducing wind speeds during tornadoes under a range of conditions including that of the roof-to-wall connections.

Could anything have been done to mitigate the damage in this EF-2 tornado? In any tornado, the highest wind speeds only occur over a relatively small proportion of the total damage path. That means damage reduction measures can be quite effective in mitigating damage from the overall storm.

If all of the houses in Barrie had been built to the building code requirements, there would have been less damage overall, although there still would have been some significant damage because of its intensity.

Strapping down

There is a better solution: the use of hurricane straps instead of toe nails. This well-established technology, developed to deal with hurricanes, can work to keep the roof attached to the walls in tornadoes with wind speeds up to about EF-2. They are inexpensive, costing less than $200 per house to install, and are easy to inspect for compliance.

Hurricane straps are a more efficient and safer replacement.

Since EF-2 and lower-rated tornadoes represent more than 95 per cent of all tornadoes, requiring straps in the building code could reduce much of the damage of these severe storms and and significantly improve safety.

While a few other things need to be done to make houses fully able to withstand EF-2 tornadoes, this adjustment would eliminate the weakest link, increasing resilience and safety by keeping the roof on the walls and stopping entire roofs from flying downwind and hitting other buildings.The Conversation

Gregory Kopp, Professor of Civil Engineering & ImpactWX Chair of Severe Storms Engineering, Western University

Thumbnail: Some of the worst damage from the EF-2 tornado that struck the Ontario city of Barrie on July 15.(Northern Tornadoes Project) Author provided

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Future hail and severe weather environment

Three model pairings (HadCM3-MM5; HadCM3-HRM3 and CCSM3-MM5) from the North American Regional Climate Change Assessment Program (NARCCAP) (Mearns et al. 2012) were used to assess future (2041-2070) hail and severe weather climate west of the continental divide based on the SRES A2 emission scenario. In addition, for the first time, a hail model (HAILCAST; Brimelow et al. 2002) was run using the NARCCAP models to explicitly project future changes in hail characteristics.

According to Brimelow et al. (2017), by midcentury, we may see an overall decrease in the number of severe weather days in southern Saskatchewan and Manitoba in the summer (with no change in the spring), though when it does occur, it could potentially be more severe (with respect to wind and tornadoes). However, changes in hail are not obvious due to the increasing height of freezing levels that tend to melt hail more readily.

The decrease in future severe weather days in southern Saskatchewan and Manitoba may be due to increased capping (i.e. warm air above the ground that inhibits storm formation). Much of Alberta may experience an increase in damaging hail in the summer, when storms do occur.

There does not appear to be much of a future change in severe hail days over southern Ontario, however, when hail does occur, it may potentially be larger (in spring, not summer) partially due to higher freezing levels, so as to melt smaller hail before it reaches the ground. In addition to larger hail, southern Ontario may also experience an earlier occurrence of large hail in the spring period.

Over all regions, the common ingredient that creates conditions for more intense storms is an overall increase in atmospheric moisture, caused by increased future warming that increases storm energy (when storms do occur). These results are broadly consistent with other U.S. research (e.g. Allen et al. 2015; Trapp et al. 2009; Van Klooster and Roebber, 2009), although future changes in the summer jet stream affecting southern Canada may not substantially decrease like the U.S. This is partially why parts of the southern Canadian Prairies may not see decreased severe weather potential in summer.


Allen, J. T., Tippett, M. K. & Sobel, A. H., 2015:  An empirical model relating US monthly hail occurrence to large-scale meteorological environment. J. Adv. Model. Earth Syst. 7, 226–243.

Brimelow, J. C., Reuter, G. W. & Poolman, E. R., 2002: Modeling maximum hail size in Alberta thunderstorms. Weath. Forecast. 17, 1048–1062.

Brimelow, J.C., W.R. Burrows and J.M. Hanesiak, 2017: The changing hail threat over North America in response to anthropogenic climate change. Nat. Clim. Change, DOI: 10.1038/NCLIMATE3321.

Mearns, L. O. et al. 2012: The North American regional climate change assessment program: overview of phase I results. Bull. Am. Meteorol. Soc. 93, 1337–1362.

Trapp, R. J., Diffenbaugh, N. S. & Gluhovsky, 2009: A. Transient response of severe thunderstorm forcing to elevated greenhouse gas concentrations. Geophys. Res. Lett. 36, L01703.

Van Klooster, S. L. & Roebber, P. J., 2009: Surface-based convective potential in the contiguous United States in a business-as-usual future climate. J. Clim. 22, 3317–3330.


Article written for the Institute for Catastrophic Loss Reduction’s (ICLR) Cat Tales, January/February 2018:

On February 15, ICLR released Hail climatology for Canada: An update. The report was written by David Etkin, Associate Professor of Disaster Management at York University.

The paper serves as an update to Etkin’s Canada’s Hail Climatology: 1977-1993, prepared for ICLR in April 2001. The update is based on an objective analysis of hail observation station data from 1977 to 2007.

National hail climatologies (i.e. the number of hail days per year in Canada) serve as a foundation for hail risk analyses. Although national hail climatologies cannot be used to determine hailstorm severity or to infer damage, they are used to help identify vulnerable regions, and thus areas where mitigation efforts should be concentrated.

Hail days data for the analysis was obtained from the Digital Archive of Canadian Climatological Data, Environment Canada from all hail observing stations in the country. For each station, monthly days-with-hail were calculated where the number of missing observations were less than four days in any month. This represents 96.7% of the records. Monthly hail days were adjusted for missing data by multiplying the unadjusted hail-day observation by the factor [1+ (number of missing days) ÷ (number of days in the month)].

A trend analysis showed no change in hail frequency for Ontario, in contrast to other studies that have examined severe hail frequency and tornado frequency. Alberta, by contrast, showed a significant increase in hail frequency during the period 1977 to 2007.

Manitoba and Saskatchewan showed decreasing trends. Future research could examine in more detail which areas exhibit increasing or decreasing hail frequencies, and how those seasons correlate with larger scale climate drivers.

Etkin warns that further hail research would be constrained by the lack of ongoing hail observations by Environment Canada. Hail observations at Environment Canada weather and climate stations were not widespread until 1977, he notes. After 1993 the number of hail observing stations began to decline and after 2005 the number of stations reporting hail dropped precipitously. After 2007, he reports, the number of observation stations was trivial. Other datasets would have to be used, such as those created by radar and satellite imagery.

In the 1990s and early 2000s, ICLR conducted a number of studies focused on understanding the risk of hail damage in Canada. The hail research needs of insurance companies was acute before ICLR was established when Canada’s most costly hailstorm struck Calgary in 1991. In particular, ICLR published an earlier hail climatology (1977-1993) and conducted several workshops where hail was considered as part of a broader discussion of convective storm-related losses.

Institute members also contributed to an industry discussion that lead to the creation of the Alberta Severe Weather Management Society.

Fortunately, there were few large hail damage events in Canada between 1991 and 2008. Indeed, there was a period of almost ten years when the Institute received virtually no requests from member companies to study the peril. The industry directed ICLR to focus its research on other hazards, including the alarming increase in water damage. Indeed, hail research was not included in the Institute’s last five-year plan.

However, hail damage claims have ramped up in Canada in recent years. Just three wind/water/hail events in Alberta (2010, 2012 and 2014) totaled more than $1.66 billion in insured losses. As a result, in 2015 Canadian property and casualty insurers – through ICLR’s Insurance Advisory Committee – formally asked the Institute to investigate the peril and suggest actions insurers can take to mitigate future hail losses in the country.

Conducting an updated climatology of hail is key to understanding the current state-of-play for the hazard before more in-depth research is pursued.

Prior to joining York University, David Etkin worked for 28 years with the Meteorological Service of Canada in a variety of fields, including operations and research. He has been an associate member of the School of Graduate Studies at the University of Toronto since 1994, doing research on natural hazards, teaching and supervising graduate students. In 2003 he was awarded the Environment Canada Award of Excellence. Prof. Etkin has participated in three international hazard projects and was one of only two non-Americans to assist with the U.S. 2nd national assessment of natural hazards. He has been principal investigator for a NATO short term project on natural hazards and disasters and the Canadian Assessment of Natural Hazards Project that resulted in the book An Assessment of Natural Hazards and Disasters in Canada, which he edited. The summary report he wrote of this latter project has been widely distributed within Canada and was used by Public Safety Canada and Foreign Affairs Canada as the official Canadian contribution to the recent ISDR Kobe disaster conference. CT

Link to report: