Climate Severity

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Environment Canada devised the climate severity index to rate a locality's climate according to human comfort and well being. The index has a range from 1 to 100, with a score of 1 representing the least severe climate and 100 the most.

The climate severity index quantifies the unfavourable aspects of the Canadian climate by weighting 17 year-round weather stressors that are generally considered to be extreme or severe. Some climate stressors include extremes of hot or cold, wetness or dryness, and windiness; poor air quality; continuous darkness or daylight; prolonged or intense precipitation, fog, restricted visibility; lightning and such severe weather as thunderstorms, blowing snow and freezing precipitation.

The climate severity index takes into account 4 major factors most directly related to environmental stress: winter and summer discomfort, psychological state, safety or hazardousness of a place, and limitations on outdoor mobility. Considering the importance of comfort in our daily lives, influencing what we wear, how we feel, if and how we travel and how effectively we work and play, this factor was considered the most important in the climate severity index. Psychological state and hazardousness are complementary factors but were judged to be of lesser importance than comfort because they are generally associated with less frequent and more ephemeral factors. Although weather restricts mobility, especially in winter, it is less significant as a year-round disruptive force than the other 3 factors.

Discomfort Factor

Winter is the most stressful time of the year in Canada. According to Statistics Canada, an average of 108 persons die each year from exposure to extreme cold temperatures, whereas 17 die from all other natural events, such as lightning, storms, floods, heat waves, earthquakes and tidal waves. The largest temperature contrasts occur during winter in Canada, while little contrast occurs during summer south of the Arctic Circle.

Three elements were used to define the winter discomfort. These subfactors are the degree of coldness (wind chill) and the duration and severity of winter. Wind chill is a recognized index of heat loss and cold injury for humans, combining the effects of low temperature and strong winds. The duration of winter is given by the number of months with mean daily temperatures less than 0° C, and the severity of winter by the mean daily temperature of the coldest month.

Summer discomfort can be defined by 4 factors: season duration (ie, the number of months with a mean daily temperature of 10° C or more); a measure of the summer's warmth (ie, the mean daily maximum temperature of the month); humidex; and dampness.

The humidex is an accepted index of summer discomfort. The mean percentage of days with a Humidex value of 30° C for one hour or more at the height of summer was used as an indicator of heat. At a humidex value of 30° C, some people become uncomfortable (below this value almost everyone is comfortable). Dampness can be expressed by the mean wet-bulb depression in July; ie, the difference between the dry-bulb and wet-bulb temperatures. The smaller this difference, the more "close" or damp the weather.

Psychological State

A wide variety of psychological complaints have been blamed upon weather. Symptoms include tiredness, depression, irritability, loss of sleep, lack of concentration, headaches, general nervousness, forgetfulness, photophobia and chest and joint pain. Weather is often blamed for spells of "cabin fever" or general monotony among personnel in isolation.

The climate elements that best represent a psychological state and yet could be readily tabulated from the primary weather data were winter day length, annual number of hours of bright sunshine, annual number of days with measurable precipitation and the frequency of hours with fog.

Long periods of darkness characteristic of high latitude winters are known to be especially detrimental - adversely affecting moods, attitudes and behaviour. Most personnel who have lived for extended periods in the Arctic quickly refer to the 24 hours of total darkness as being particularly debilitating. Some even suggest that the converse in summer, 24 hours of continuous light, is wearing at times.

Sunshine has important physiological and psychological implications. Clear, sunny weather, occurring especially at the end of a long spell of overcast, can be mentally uplifting. Frequent wet or foggy days can be demoralizing. This is especially true for northern residents, who feel discouraged if precipitation occurs frequently during the warmest time of the year, since they have to endure a long winter before enjoying a few days of warm summery weather.

Hazardousness

Elements of climate either singly or together can produce widespread injury and death and bring about considerable damage to property and the environment. Obvious examples are floods and blizzards, which may seriously disrupt entire communities. Extreme wind chill in winter and excessive heat and humidity in summer are also hazardous.

The general hazardousness of a locality could be measured by considering the average winter snowfall and the frequencies of 3 other elements: strong winds, thunderstorms and blowing snow. These phenomena can cause a whole host of personal hardship, including possible death, injuries, missed social and business events, delayed services and other privations. Thunderstorms in particular are good indicators of severe weather; eg, hail, windstorms and tornadoes. Blowing and drifting snow create dangerous outdoor travel conditions, stranding people in perilous and precarious situations. In fact, all outdoor activity becomes extremely hazardous if near-zero visibilities in blowing snow are combined with high wind chill. Under such conditions farmers have become lost and died of exposure while attempting to walk from the barn to the house.

Outdoor Mobility

Our ability to move about, to travel to work, school and shopping is restricted by adverse weather. Three subfactors were identified as restricting outdoor travel and access: total snowfall, limiting visibility and freezing precipitation. In Canada, snowfall must be taken into account for assessing the ease of outdoor movement on foot and by vehicle. Freezing precipitation restricts all forms of transportation from walking to flying. In addition, it frequently plays havoc with communication owing to downed telephone and hydro wires.

Climate Severity Index

For 146 airport locations in Canada, points were assigned for 17 weather elements depending on extremes, intensity and duration, and the totals were summed and weighted to get the climate severity index. For example, a station with long winters (mean daily temperature less than 0° C lasting 10 or more months) was assigned full points for length of winter, whereas one with no months meeting the criteria was assigned zero points for this subfactor. The sum of the 17 subfactors for each of the 4 major factors, weighted by the importance of each factor, yielded the degree of climate severity for that station. The climate severity index is designed so that values approaching 100 indicate the highest severity.

In Canada, much of the northern Queen Elizabeth Islands, except for some sheltered locations, have the highest severity, with all 4 factors showing high values. Only slightly less severity exists in the remainder of the Arctic Islands, the Beaufort Sea coast, the District of Keewatin, northern Manitoba, the Hudson Bay coast of Ontario, the Ungava Peninsula and the Hudson Strait shores of Québec and northern Labrador.

Over the remainder of Canada, the severity values are much lower. Victoria (13) and Penticton (16) are among the most pleasant climates of Canada's populated places. Medicine Hat (29) and Lethbridge (33) are relatively benign.

The accompanying Climate Severity Indexes of Selected Placeslists climate severity index values for some of Canada's major cities. Victoria has the best climate in the country. St John's (56) wins the prize for the city with the toughest climate. The honour of having the absolute worst climate in Canada goes to a place that no longer exists, Isachsen weather station in the NWT (see High Arctic Weather Stations). It had a CSI of 99. Isachsen was closed down in 1978.

These values are estimates for central city locations. In some cases, there are differences between these and the values estimated for airport sites.

The climate severity index is an indicator of the year-round rigours created by climate. It is not an absolute measure, since any such measure would involve subjective value judgements that cannot be precisely quantified.

Climate Severity Indexes of Selected Places