Chapter 1
1. URBAN TORNADOES IN CANADA
The public has not forgotten the devastating tornado of Friday, July 31, 1987 which struck Edmonton, Alberta (1987 population 584000, 53o 34'N, 113o 31'W, elevation 680 m). The tornado killed 27 people, hospitalized 53 more, and caused injuries requiring treatment at 6 hospitals to approximately 250 others. Fatalities were confined to the industrial area (12) of east Edmonton and Strathcona County and to the Evergreen Mobile Home Park (15), where 133 homes were destroyed, in rural northeast Edmonton.
At 1455 Mountain Daylight Time (MDT), the Alberta Weather Centre (ALWC) received its first report about the tornado from a viewer 10 km south of the city. The ALWC transmitted a Tornado Warning at 1504 MDT, approximately 25 minutes before the first fatality occurred. Because of communication problems, many radio stations received their first reports about the tornado from their listeners (Hage, 1987a).
a. An outbreak of tornadoes in Ontario, in retrospect
On Friday, May 31, 1985, 2 tornadoes killed 12 people in southern Ontario: 8 in Barrie, 2 in Grand Valley, and 2 in Tottenham (Newark, 1985). These were 2 of 7 tornadoes to traverse southern Ontario that day (Lawrynuik et al., 1985; Leduc et al., 1986), and all occurred where power and telephone service had, in general, been lost. The 7 tornadoes touched down 13 times (Witten, 1985). At nearly the same time as the last fatality occurred, 1700 Eastern Daylight Time (EDT), the Ontario Weather Centre issued its first Tornado Warning, though in the previous 2.5 hours it had issued several Severe Thunderstorm Warnings, each including a note that tornadoes could develop (Leduc et al., 1986). Also at 1700 EDT, the first of 28 tornado touchdowns south of the Great Lakes occurred near Lake Erie on the Ohio- Pennsylvania border. Before sunset, tornadoes had caused 17 deaths in Ohio and 65 deaths in Pennsylvania (Witten, 1985). Not surprisingly, residents of Ontario, Ohio, and Pennsylvania refer to May 31, 1985 as "Black Friday", a term frequently used by Albertans to refer to the day of the Edmonton tornado.
Carter et al. (1989a) conducted an epidemiological study for the regions affected by the Ontario tornadoes. Social workers surveyed most of the injured, and the fatalities were surveyed by proxy. Affected but uninjured people were also surveyed, and their responses were used as matched controls. Forty-eight people were hospitalized with serious injuries, including 2 who were still disabled 2 years later, and an additional 233 people were treated in emergency rooms. The seriously injured spent a total of approximately 600 days in acute care. In an unpublished epidemiological study of the Edmonton tornado, Carter et al. (1989b) found that 46 seriously-injured people spent a total of 930 days in acute care.
Fortunately, the Ontario tornadoes did not strike a mobile home park. Carter et al. (1989a), however, found that 5 of the 6 people killed in residences were in buildings where the ground floors became airborne, a common event when violent winds buffet a mobile home park. Hundreds of houses were subjected to the winds of the Ontario tornadoes, but the floors of just 22 houses became airborne. Of these 22 houses, only 2 were known to have been built to the pertinent anchorage requirements of the National Building Code of Canada (Carter et al., 1989a; Allen, 1986). Lux (1990) concluded that the Edmonton tornado did not lift the ground floor of a frame house.
Ontario Tornadoes, May 31, 1985 (Harris, 1985) includes hundreds of photographs with detailed captions and, of particular interest to researchers who study the behavior of people encountering disasters (such as those who contributed to Handmer and Penning-Rowsell (1990)), dozens of stories from people who wished to relate their experiences.
b. Studying the Edmonton tornado
A survey form was published by Edmonton's 2 daily newspapers (combined circulation 293,000) just 8 and 9 days after the tornado. It gave citizens of central Alberta an opportunity to tell their stories to meteorologists at the University of Alberta and to future generations. A map of reported hail-size categories and a preliminary analysis of perceived warning times, both derived from the 815 responses to the survey, have already been published (Hage, 1987a; Charlton et al. 1990; Charlton et al. 1995).
The Edmonton tornado has been examined from a variety of perspectives. The official review of the local severe- weather-warning system by Hage (1987a) included a survey of the damage path, analysis of the weather conditions during the day of the tornado, commentaries by ALWC forecasters specializing in severe weather, and the results of a telephone survey conducted 6 weeks after the tornado to determine the public's perceptions of the severe-weather-warning system. In response to the conclusions published in the Hage report, an operational Doppler radar system was installed near Edmonton in 1991, the first in Western Canada. The first Doppler radar system in Canada, now used for both research and operations, was installed at King City, north of Toronto, in 1985 (Nichols and Crozier, 1989).
A householder survey of people who lived in 2 areas where the tornado passed through was conducted 70 weeks after the event; their recoveries were studied and the results were incorporated into an unpublished Doctoral dissertation for the Department of Educational Psychology, University of Alberta, by Caine (1989). The transportation of the injured to city hospitals was investigated by Scanlon and Hiscott (1994). The experiences of some of the injured were described in an article about the tornado in Reader's Digest (Tower, 1989). Reports from emergency response agencies, the Insurance Bureau of Canada, and utility companies were published in Tornado: A Report (Alberta Public Safety Services, 1990). The report also included a discussion of the climatology of tornadoes in Alberta by K. D. Hage and a brief review of the weather warning system by A. F. Wallace, the severe weather coordinator at the ALWC. The unedited versions of the submissions to Tornado: A Report were placed in file 89-340 at the Alberta Archives. Other publications by forecasters at the ALWC, the main forecasting office in Alberta, described the weather systems that traversed Alberta on July 31 and the area damaged by the tornado (Bullas and Wallace, 1987; Atchison, 1988; Paruk, 1988). The difficulties that insurance companies experienced in settling claims were documented by Deibert and Wood (1988). An assessment of building damage was conducted by Lux (1990), a structural engineer who also provided information to Carter et al. (1989b). The scattering and subsequent clean-up of hazardous materials were reported by Holmes (1989, 1990) of Alberta Public Safety Services. A Master of Science thesis by De Serres (1996) applied the theory of crisis management to the Edmonton tornado.
Between 1500 and 1605 MDT, the tornado, moving from south to north through east Edmonton, left a continuous damage swath 37 km in length, ranging from 100 m to more than 1000 m in width. Immediately to the west, an area of 125 km2 was struck by tennis ball-sized hail. According to Alan Wood, the regional vice- president of the Insurance Bureau of Canada (Edmonton office), there were 60000 successful automobile and building insurance claims, and 50000 of these were paid for hail damage. Numerous reports of giant hailstones were carried by the media, and 1 of the hailstones recovered by a citizen set a new Alberta mass record. At least 2 individuals in south Edmonton were rendered unconscious by blows from hailstones. In Urban Hailstorms: A View From Alberta, Charlton et al. (1995) described the weather events across the province for the day of the Edmonton tornado and compared the 1987 Edmonton storm with 8 major urban hailstorms, 4 in Alberta and 4 outside Canada.
This paper includes a set of detailed maps showing the areal distribution of various storm-related parameters within the Greater Edmonton region (Edmonton, St. Albert, and Sherwood Park). These maps are apparently unprecedented for studies about tornadoes and hailstorms. Numerous new sources are used to supplement the information gathered from the newspaper survey; these sources include photographs from air surveys, the records of two roofing companies, and the results from the telephone, householder, and epidemiological surveys. Tabulations of flooding and sewer blockage incidents and rainfall rates, all obtained from the Water and Sanitation Department (EWS) of the City of Edmonton, are also used.
c. Canadian studies of urban tornado climatology
In addition to the Ontario tornadoes of May 31, 1985, Newark (1985) listed 4 other Canadian tornadoes or series of tornadoes that have caused tragedies: 9 people were killed in Windsor, Ontario on April 3, 1974; 17 perished in Windsor on June 17, 1946; 28 died in Regina, Saskatchewan on June 30, 1912; and, 9 or 11 people lost their lives between St. Zotique and Valleyfield, Quebec on August 16, 1888.
From his exhaustive examination of newspapers and local histories from Alberta and Saskatchewan, Hage (1990) determined the numbers of tornadoes that struck Edmonton and Calgary, Alberta and Regina and Saskatoon, Saskatchewan from 1890 to 1989: Edmonton had 12, Calgary, 3, Regina, 17, Saskatoon, 10. Similarly, Hage (1987b) provided the numbers for Moose Jaw (6), Saskatchewan, and Lethbridge (2) and Medicine Hat (4), Alberta, for 1910 to 1960. For the period 1879 to 1984, Hage (1994) published a booklet about Alberta that contained a list of the occurrences in which deaths, injuries, or property damage were caused by tornadoes, windstorms or lightning. These incidents were organized by types of events and dates. He was preparing a similar volume in 1995 using information for Saskatchewan. Estimates of the numbers of tornadoes that struck 11 Canadian cities during climatological periods of varying lengths were performed by Murray (1990). Newark and McCulloch (1992) used tornado climatologies to determine the risk, weighted by population, for each of 49 Canadian cities. They suggested that their calculations should be used to plan a Doppler radar network for Canada. Etkin (1995) discussed the apparent increase in the frequency of tornadoes in Western Canada. Joe et al. (1995) reviewed techniques used by Environment Canada to forecast the development of severe storms.