To access the other concept sheets in the Cities Subject to Natural Hazards unit, check out the See Also section.
Climate hazards are natural hazards that result from climate phenomena.
A tornado is a funnel of violent winds that extends from the base of a cloud to the ground.
Tornadoes are difficult to predict, move quickly and their trajectory is totally unpredictable. With winds clocking up to 500 km/h, tornadoes can uproot trees, roll cars and destroy houses. They sometimes also bring heavy rain and hail and present a serious risk to the lives of those in their path.
Tornadoes more often occur in the USA and in Canada than anywhere else.
Source: Jonah Lange, Shutterstock.com
In 1971, Dr. Ted Fujita invented the Fujita Scale to categorize tornadoes based on an estimation of their wind speed and the damage caused. In early 2002, scientists realized there were deficiencies in the original scale and developed the Enhanced Fujita Scale. This scale has been used in the United States since 2007, and in Canada since 2013.
| Category | Wind speed | Possible damage |
|---|---|---|
|
F0 |
104 to 137 km/h |
|
|
F1 |
138 to 177 km/h |
|
|
F2 |
178 to 217 km/h |
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F3 |
218 to 266 km/h |
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F4 |
267 to 322 km/h |
|
|
F5 |
322 km/h and over |
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Source of the data: The Weather Channel, 2020[12]. |
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Photograph of the Destruction Caused by an F4 Tornado That Touched Down in the City of Tuscaloosa, Alabama, in the United States.
Source: Gregory Simpson, Shutterstock.com
The Enhanced Fujita Scale is used in Canada but has been modified so that it is better adapted to the country’s reality. To find out more, check out the page Enhanced Fujita scale for wind damage.
The United States records the highest number of tornadoes in the world each year. According to the National Oceanic and Atmospheric Administration (NOAA), there are more than 1200 tornadoes every year[1]. The country sometimes experiences outbreaks of tornadoes. This occurs when there is a very large number of tornadoes over a short period of time. One of the worst stretches occurred in April 2011. It was considered a super outbreak because between August 25 and 28, more than 350 tornadoes formed in different central and eastern states of the country. Many of them were classified F4 and F5 on the Enhanced Fujita Scale. In total, the outbreak caused more than $12 billion in damage[2].
A flood occurs when a large quantity of water occupies a territory that is usually dry.
Floods are the most common climate-related natural disasters. They can occur in a few minutes or hours, and can last up to weeks.
A flood can be caused by different factors:
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heavy rainfall
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rapid snow melt
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a storm surge that accompanies cyclones, typhoons and hurricanes
The most dangerous types of floods are flash floods. They occur when a very large quantity of rain falls in a short period of time and the soil does not have the capacity to absorb all the water. They are often quite serious and occur in a matter of minutes. Flash floods take people and authorities by surprise, which is what makes them dangerous.
Between July 25 and 30, 2022, eastern Kentuky was hit by several storms, accompanied by heavy rainfall. In five days, 35 to 40 cm of rain fell in the region, most of it during the night of July 27 to 28. In some places, close to 10 cm of rain fell per hour. This torrential rain caused flash floods in several areas. These massive flash floods carried entire houses away and transformed roads into rivers, causing 39 deaths[3]. The search for people who disappeared lasted several days. More than 300 people lost their homes and 12 000 people had no electricity.[4]
Floods affect more countries than any other natural disaster. One house in five is at risk of being flooded.
Check out the Government of Canada website and the video on flood risks to find out more.
Source: EB Adventure Photography, Shutterstock.com
Winter storms occur anywhere in the world that has a cold, continental or temperate climate. It can take three different forms:
A snowstorm can completely paralyze a city for a few hours or even a few days. The accumulation of snow can make travel difficult, or even dangerous and impossible. A snowstorm’s impact depends on its location. For example, regions that generally receive a lot of snow have measures in place to quickly remove it from streets and sidewalks.
Extreme cold can occur during the winter and is also dangerous for those who are not used to it. Cold warnings are adapted to the climate of each region. In Quebec, an extreme cold warning is issued when the temperature drops to -38°C for at least two hours, while in Ontario, an extreme cold warning is issued when the temperature is expected to fall to -30°C[8].
Source: Barisev Roman, Shutterstock.com
In Quebec, an average of 275 cm of snow falls in the winter, however, the quantity varies from region to region. In Montreal, the average is 175 cm of snow, while in Quebec City, it is 300 cm. The Laurentians get more than 600 cm of snow in the winter[7]. For Quebec, the Meteorological Service of Canada sends a heavy snow warning only when more than 15 cm of snow is expected in 12 hours or less. Planning and preparing snow-removal operations allows people to go about their daily routines.
Inversely, places that are not used to getting snow or that get very little, like Washington and Atlanta, in the United States, or even Vancouver, Canada, are paralyzed by a few centimetres of snow.
To find out more, check out the following article.
A blizzard ressembles a snowstorm, but is accompanied by high winds, which leads to low visibility.
According to the Meteorological Service of Canada (MSC), a blizzard is a snowstorm that lasts at least six hours, with wind speeds of more than 40 km/h. These strong winds lead to drifting snow, which can reduce visibility to less than one kilometre[5].
Like all winter snowstorms, blizzards occur in places where the temperature drops to below zero. In Canada, blizzards are most common in the Prairies and the Maritimes.
Drifting snow is fine snow that is lifted and carried by the wind.
An ice storm occurs when there is freezing rain, which is a form of rain that freezes instantly when it comes into contact with the ground or an object. The layer of ice formed is called glaze or sheet ice.
Freezing rain is fairly difficult to predict. It is dreaded because the layer of ice can make surfaces extremely slippery, slowing down traffic and causing major accidents. Sidewalks also become very dangerous for pedestrians. The weight of the ice can damage electrical lines, tree branches, and so on.
Source: ilmarinfoto, Shutterstock.com
Between January 4 and 10, 1998, an ice storm battered southern Quebec and part of Ontario. Up to 100 mm of freezing rain fell in certain regions of the St. Lawrence Valley, double what these regions usually get in one year. It was one of the worst natural disasters in Canadian history.
Many roads were closed, cutting off entire villages. There were major power outages and almost 1.4 million Quebecers were without electricity in the middle of winter. This storm caused 35 deaths, 945 people were injured and more than 600 000 people were temporarily displaced, causing approximately $5.4 billion in storm-related costs.
The federal government sent the Canadian Armed Forces to assist in setting up shelters and medical services, and to help restore the electricity grid. More than 15 000 soldiers provided backup during the 1998 ice storm, the largest peace-time deployment of troops in Canadian history[9].
Hurricane, typhoon and cyclone are different names given to the same meteorological phenomenon. The name changes depending on where the storms occur.
Source: elRoce, Shutterstock.com
A cyclone is a violent storm that originates in the oceans close to the Equator. It can also be referred to as a typhoon or a hurricane depending on the region where it forms.
Cyclones, hurricanes and typhoons are violent storms characterized by strong winds and lots of rain. They form in the ocean close to the equator, meaning between the 30th parallel north and 30th parallel south. The temperature must be fairly high to lead to the formation of a storm. Their trajectory varies according to meteorological conditions. Some storms stay in the ocean, while others hit certain islands as well as the coasts of continents. In general, scientists are able to estimate the trajectories of these storms.
When these storms hit coastal areas, they can cause enormous damage. Strong winds, heavy precipitation and waves can cause floods, flatten buildings, damage electrical lines and much more. In areas where the population is not adequately prepared, these storms can also lead to many deaths.
| Hurricane | Cyclone | Typhoon | |
|---|---|---|---|
| Location | Atlantic Ocean and in part of the Pacific Ocean | Indian Ocean and the southern Pacific Ocean | Northwestern Pacific Ocean |
| Period | June to December | April to December | End of June to December |
Scientists and meteorologists use the Saffir-Simpson Scale to categorize these storms. Hurricanes, typhoons and cyclones are rated from 1 to 5, mostly based on wind strength.
When winds are below 63 km/h, it’s considered to be a tropical depression. This becomes a tropical storm when the winds are between 63 and 118 km/h. According to the World Meteorological Organization, these storms become hurricanes, typhoons or cyclones when the winds reach 119 km/h or higher[6].
| Category | Wind speed | Description of Damage |
|---|---|---|
|
1 |
119 to 153 km/h |
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|
2 |
154 to 177 km/h |
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3 |
178 to 208 km/h |
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4 |
209 to 251 km/h |
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5 |
252 km/h or higher |
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Source: National Hurricane Center, n.d.[11] |
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Hurricane Dorian battered the Bahamas from September 1 to September 3, 2019. The category 5 hurricane caused devastating damage to several islands in the archipelago. The winds reached 300 km/h and the heavy rainfall caused major flooding. More than 13 000 houses were destroyed, several roads were seriously damaged and close to 70 000 people were affected. Some of the islands were without drinking water and electricity for several days.
On October 18, 2019, a total of 67 deaths had been recorded, but one year later, hundreds of people were still reported missing[10].
Source: Paul Dempsey, Shutterstock.com
To access the rest of the unit, you can consult the following concept sheets.
- National Severe Storms Laboratory. (n.d.). Severe Weather 101 - Tornadoes. National Oceanic and Atmospheric Administration. https://www.nssl.noaa.gov/education/svrwx101/tornadoes/
- Hirschlag, Ally. (2022, March 10). 9 Record-Breaking Tornado Stats. The Weather Channel. https://weather.com/safety/tornado/news/2021-03-19-record-breaking-tornadoes-us
- National Weather Service. (n.d.). Historic July 26th-July 30th, 2022 Eastern Kentucky Flooding. National Oceanic and Atmospheric Administration. https://www.weather.gov/jkl/July2022Flooding
- Associated Press. (2022, 1August 1). Le bilan des inondations s’alourdit au Kentucky. Radio-Canada. https://ici.radio-canada.ca/nouvelle/1902543/kentucky-pluie-inondations-morts-sauvetage
- Maybank, J. (2015, March 4). Blizzard. L’Encyclopédie canadienne. https://www.thecanadianencyclopedia.ca/fr/article/blizzard
- Mayer, Nathalie. (2017, 17 septembre). Échelle de Saffir-Simpson : qu’est-ce que c’est?. https://www.futura-sciences.com/planete/definitions/meteorologie-echelle-saffir-simpson-3619/
- Ministère de l’Environnement et de la Lutte contre les changements climatiques. (n.d.). Normales climatiques 1981-2010. Gouvernement du Québec. https://www.environnement.gouv.qc.ca/climat/normales/climat-qc.htm.
- Gouvernement du Canada. (2020, October 29). Critères d’alertes météo publiques. https://www.canada.ca/fr/environnement-changement-climatique/services/types-previsions-meteorologiques-utilisation/publiques/criteres-alertes-meteo.html#froidExtreme
- Bonikowsky, Laura Neilson, Block, Niko. (2016, February 11). Tempête de verglas de 1998. L’Encyclopédie canadienne. https://www.thecanadianencyclopedia.ca/fr/article/la-crise-du-verglas-1998
- Lacroix, Camille. (2020, September 29). Les Bahamas se relèvent un an après l’ouragan Dorian. Perspective Monde. https://perspective.usherbrooke.ca/bilan/servlet/BMAnalyse?codeAnalyse=2899.
- National Hurricane Center. (n.d.). Saffir-Simpson Hurricane Wind Scale. National Oceanic and Atmospheric Administration. https://www.nhc.noaa.gov/aboutsshws.php
- The Weather Channel. (2020, April 9). The Enhanced Fujita Scale: How Tornadoes are Rated. https://weather.com/storms/tornado/news/enhanced-fujita-scale-20130206