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An Investigation Into The Impacts Of Tornadoes In Canada Tornados

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Tornadoes are one of the most impressive and powerful forces of nature. They can strike quickly with little warning, and cause millions of dollars in damages and even death. It is these powerful impacts that have led to the fascination that storm chasers have with discovering the inner workings of tornadoes. The focus of this term paper will be to investigate the natural hazard known as tornadoes. It will follow the framework for Analysis of Human Adaptation to Natural Hazards. This will include biophysical dimensions of tornadoes, human use of the affected environment, a consideration of the environmental change caused by tornadoes, and the human response to tornadoes.

Although they are rarer and have smaller damage paths than other natural hazards, tornadoes represent a significant hazard because of their unpredictable and rapid onset of violent winds, reaching devastating levels within minutes. Tornadic thunderstorms are the most damaging type of weather faced by Canadians and are of great interest to the human population because of the major social, economic and environmental impacts they impose on our lives.

When you think of Canada, the thought of tornadoes as a natural hazard does not necessarily come to mind. Surprisingly, Canada experiences the second most tornadoes out of any other country in the world. It is interesting to note that the average number of tornadoes increases every year. Most tornadoes occur during the spring and summer months, with June and July having the highest frequency. Despite this pattern, there have been a few cases of tornadoes touching down around winter time. Tornadoes will usually develop in the mid-afternoon to early evening.

Tornadoes are essentially a whirlpool of converging opposites, where upwelling warm air confronts down tumbling cool air, dry air encounters moist, and winds aloft collide with winds below. In nature this produces torrential rains, dangerous lightning, hailstorms and winds up to 300 mph. (Bernanke, 1994). These conditions occur when cold polar air comes in contact with warm moist air from the Gulf of Mexico. This is the main reason why eastern Canada receives more thunderstorms and tornadoes than western Canada. A tornadoes diameter at the earth's surface is usually from 100 to 600 m, but in the case of more violent winds the diameter has exceeded 1.6 km. Tornadoes usually remain in contact with the ground for only short distances rarely more than 25 km. Their forward motion averages 70 km/h, but they have been known to exceed 100km/h.

To make tornadoes even more hazardous, they commonly occur in families; a single line of thunderstorms can create numerous tornadoes. On May 31, 1985 a family of seven tornadoes traveled through South-western Ontario extensively damaging Barrie, Orangeville and Grand Valley. Twelve people were killed, 155 were injured, and total damage was estimated at $100 million (Etkin, 1997).

Theodore Fujita, a man whose research formed the cornerstone of tornado science, developed a scale for classifying the intensity of tornadoes. The Fujita scale is broken down into the following classes: F0 and F1 (weak, with winds less than 180 km/h); F2 and F3 (strong, with winds 181-332 km/h); F4 (violent, with winds over 333 km/h); and F5 (over 420 km/h) (Christopherson, 2001). Damage can range from broken tree branches in the case of F0 tornadoes to houses being uplifted and cars being tossed like missiles in F5's.

Human Use of the Affected Environment

Humans occupy many areas that are vulnerable to tornadoes and severe weather.

In Canada, tornadoes most frequently affect the Prairie Provinces and Ontario. Extreme Southwestern Ontario has the highest tornado frequency in Canada, with approximately 10 events per year per 10,000 km2. The regions of Southern Ontario with the highest tornado frequency have patterns that are a function of topography and proximity to lakes and their on-land breezes (Judd, 1998). Development in this area has been influenced by freshwater resource of the Great Lakes and by its vast farmland.

The bulk of tornadoes occur in the southern regions of the afflicted provinces due to patterns of warmer temperatures required for convection to occur. The peaks occur in extreme southern regions, with definite higher frequencies clustered around major cities. The clustering occurs where higher populations are present to witness and report the events, and distributions are much lower in the peripheral zones. Canada is sparsely populated in areas, allowing tornadoes in rural regions to go undetected, unwitnessed, or merely unreported because of either no, or low damage (Judd, 1998).

Humans inhabiting areas prone to tornadoes are in a vulnerable position. Without being able to accurately predict them, people in the path of a tornado may not be alerted until it is too late. People in mobile home parks and cottages are most vulnerable to the violent winds because they are generally not anchored and are constructed to lower standards. Even houses may collapse in the event of a tornado if the walls are improperly anchored to the foundation or if the roof is not secured.

Canada, unlike the United States, does not receive many of the more damaging tornadoes. From 1918 to 1992, Canada recorded no F5's and only 8 F4's. It seems that tornadoes in Canada do not occur often enough to deter people from living in affected areas and when they do occur they are generally classified as weak, ranging from F0 to F2. The return period for severe tornadoes (F3 or stronger) in Southwestern Ontario is five years. This means a disastrous tornado can be expected in the populated area of Ontario once in five years (Eisen, 2000).

Environmental Change

Tornadoes can have harmful physical impacts on the environment when they strike with incredible velocity. The winds are powerful enough to snap and uproot trees, destroying forests in their paths. Tornadoes and the torrential rain and hail that accompany them can destroy a vast amount of crops. Winds of up to 300 mph can turn harmless objects and structures into deadly projectiles, all occurring in a matter of seconds. Injuries or deaths resulting from tornadoes are most often caused by the collapse of buildings and flying debris.

The greatest physical damage occurs when tornadoes rip through populated areas. The destruction of these areas leaves an aftermath of garbage and debris, including harmful household chemicals. In the case of devastating tornadoes, waste disposal action plans must be put in place to ensure debris and hazards are removed from the environment and disposed of safely.




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