Forensic Damage Assessment of a $3 Billion Urban Hailstorm – August 5, 2024 Calgary, Alberta, Canada

On August 5, 2024, a major wind-driven hail event hit northern portions of the City of Calgary, Alberta—Canada's 5^th most populous metropolitan area. Large volumes of hail with maximum diameters of 40 to 50 mm were accompanied by outflow winds gusting from 65 km/h to possibly over 100 km/h. This affected residential, commercial and industrial areas, as well as the international airport. With an estimated insured loss of $3.25 billion CDN, this event is both the costliest hailstorm and the costliest severe convective event in Canadian history.

On the day following this event, the Northern Hail Project (NHP) deployed its Rapid Response Survey (RRS) for Major Urban Hailstorms, executing what is likely the most thorough damage survey of an urban hailstorm in North America. First, a team was deployed to conduct a scouting mission, locating the worst affected areas, as well as defining the boundaries of urban hail impacts. Following this, a rotating group of three teams was deployed to document— through extensive ground and aerial surveys— impacts in the worst affected areas. These teams made 49 drone flights, conducted over 100 eyewitness interviews, and drove over 1000 km. This was supplemented by outreach (using phone and social media) for locations with limited access, and by consultation with roofing and building repair companies.

The survey documented damage to residential and commercial buildings, vehicles and other assets. Information was collected on damage to a variety of residential roofing and siding materials, including hail-resilient products. Single-, double- and triple-pane building windows were broken. Water penetrated the flat roofing systems of commercial and industrial buildings. Vehicle damage (~1/3 of the insured loss) was recorded in residential areas (personal and fleet vehicles) and vehicle storage lots. Notable damage at Calgary’s International Airport included roof damage and water penetration, as well as severe damage to dozens of commercial aircraft.

Damage information will be compared to hail data from multiple sources, including hail samples collected by the NHP, and disdrometer stations within the CSSL’s disdrometer network. Findings will be used to support and refine the identification of hail-resistant construction materials, and to inform risk reduction measures and hail event scenario modelling. Our findings indicate that, given the significant amount of damage from this event and the potential for even worse hailstorms to hit the city, much greater damage could result from future events unless widespread damage reduction measures are implemented across Calgary.