EXTREME HEAT

Environment Canada does not issue warnings for extreme heat, but does issue Humidex advisories for heat in combination with high humidity.

A Humidex Advisory is issued by Environment Canada in Ontario when both of the following conditions are forecast to occur:

• the maximum temperature is expected to reach or exceed 30°C

• and the humidex is expected to reach or exceed 40

HEAT WAVES

A heat wave is defined as follows by the World Meteorological Organization (WMO):

• Marked warming of the air or invasion of very warm air, over a large area; it usually lasts from a few days to a few weeks.

In Canada:

• Three or more consecutive days in which the maximum temperature is greater than or equal to 32°C.

HUMIDEX

Humidex is an index to indicate how hot or humid the weather feels to the average person. It is essentially an 'equivalent' temperature that the body feels given the actual air temperature and relative humidity or moisture content of the air. The higher the humidex, the harder it is for perspiration to evaporate and cool the body.

Humidex is derived by combining temperature and humidity values into one number to reflect the perceived temperature. (Note that although the humidex is a dimensionless number, the number indicates an approximate temperature in °C.) For example, a humidex of 40 means that when the temperature is 30°C and the air is humid, the average person feels more or less the same as when the temperature is 40°C and the air is dry.

Humidex was a Canadian innovation, introduced in 1965. Using a formula developed by Environment Canada in 1979, humidex can be calculated from air temperature and dewpoint temperature:

humidex = (air temperature) + h
where h = (0.5555)*(e - 10.0);
e = vapour pressure in hPa (mbar), given by:
e = 6.11 * exp [5417.7530 * ( (1/ 273.16) - (1/ (dewpoint) ) ]

where dewpoint is expressed in kelvins (temperature in K = temperature in °C + 273.1) and 5417.7530 is a rounded constant based on the molecular weight of water, latent heat of evaporation, and the universal gas constant.

Environment Canada defines the degree of “discomfort” associated with the humidex in specific ranges: (see Environment Canada, 2002d):

• Above 45 Dangerous
• 40 - <45 Great Discomfort
• 35 - <40 Some Discomfort
• 30 - <35 Some Discomfort

Heat stroke is imminent if the humidex exceeds 54. The highest humidex recorded at hourly weather observing stations in Canada occurred in Windsor, Ontario on June 20, 1953: a value of 52.1.

HEAT-HEALTH ALERT SYSTEMS

Several municipalities in Ontario have initiated Heat-Health Alert Systems to warn the population of potentially dangerous high temperature related conditions, and to generally increase services to the general public by providing information about heat exhaustion, heat stroke and the impact of heat, sun and smog on pre-existing health conditions. When the Alerts are issued, the municipality's designated alert team response could involve community groups, agencies, facilities/ hospitals, local shelter site(s) and "cooling centres", and the media, which act to coordinate a variety of community services. The following list of websites provides information on Heat-Health Alert Systems that have been initiated in the cities of Ottawa and Kingston as well as in the Regions of Waterloo and Halton. (For information on Toronto's Heat-Health Alert System, please refer to the next section of this document.) Please note that while this list is not meant to be exhaustive, it gives a representation of the Heat-Health Alert Systems currently in place in portions of Ontario.

http://www.ottawa.ca/ residents/ health/ environments/ issues/ hot/ heat_alert_en.html

http:// www.cityofkingston.ca/ residents/ environment/ extreme/ heatlevels.asp

http:/ /www.kflapublichealth.ca/ Files/ Resources/ Extreme_Heat_ Health_Response_ Plan.pdf

http:// www.region.waterloo.on.ca/ WEB/ health.nsf/ c56e308f49bfeb7885256abc0071ec9a/ 62f7de0d34d34d3885256bcd006355e3!OpenDocument

http:// www.halton.ca/ cms/ one.aspx? portalId=8310& pageId=13692

Although the specific criteria for heat (and smog) related alerts will vary by municipality, these alerts are issued, for example, by the regions of Waterloo and Halton when specific advisories are issued by Environment Canada and the Ontario Ministry of the Environment (MOE):

• Heat Alert - when Environment Canada issues a Humidex Advisory for the region.

• Smog Alert - when MOE and Environment Canada issue a Smog Advisory for the region.

• Smog and Heat Alert - when both of the above Advisories are issued for the region.

Similarly, Kingston, Frontenac and Lennox & Addington (KFL&A) Public Health issues a Level 1, 2 or 3 Heat Advisory based on the issuance of specific humidex thresholds with or without the issuance of smog advisories. The issuance of a Heat Advisory under the City of Kingston's Extreme Heat Response Plan invokes three levels of action that coordinate the efforts of community agencies to provide services that will help residents deal with the extreme heat. The extreme heat thresholds defined in the Heat Advisory system are:

• Level 1: Heat Alert:

  - when the humidex is forecast to be 36 or greater for at least two consecutive days and there is no Smog Alert

• Level 2: Heat Warning:

  - when the humidex is forecast to be 36 or greater for at least two consecutive days and a Smog Alert is in effect

  OR

  - when the humidex is forecast to be 40 or greater for at least two consecutive days and there is no Smog Alert

• Level 3: Heat Emergency:

  - when the humidex is forecast to be 36 or greater for at least two consecutive days with other contributing factors (i.e. power outage) and a Smog Alert is in effect

  OR

  - when the humidex is forecast to be 40 or greater for at least two consecutive days and a Smog Alert is in effect

  OR

  - when the humidex is forecast to be 45 or greater for at least two consecutive days and there is no Smog Alert

(see http:// www.cityofkingston.ca/ residents/ environment/ extreme/ heatlevels.asp and http:// www.kflapublichealth.ca/ Files/ Resources/ Extreme_Heat_ Health_Response_ Plan.pdf for the actions associated with each level)

Ottawa's Hot Weather Response Plan is a two level alert system which is initiated when specific humidex thresholds are forecast by Environment Canada:

• Heat Alert - when the humidex is forecast to be 36 or greater for at least two consecutive days.

• Extreme Heat Alert - when the humidex is forecast to be 40 or greater for at least two consecutive days

TORONTO'S HEAT-HEALTH ALERT SYSTEM

An earlier version of Toronto's present day Heat Alert system was initiated in 1999. Under this system, an Alert was called by the City when the Humidex reached 40 or greater for two or more consecutive days. In 2001, the City of Toronto Public Health Department, in partnership with the Toronto Atmospheric Fund, Climate Change Action Fund and with assistance from Environment Canada and the University of Delaware, received federal support to develop a new Heat Alert and Emergency system. Based on statistical and epidemiological evidence, the primary benefit of this new system is to more accurately link warm season climatic factors to an increased risk of elevated mortality from heat impacts. Researchers found that certain climatic conditions were associated with significantly higher rates of death in Toronto. They also determined that the impacts of heat in Toronto (as reflected in mortality statistics) are greater for heat events early in the warm season (e.g. April - May) and for persistent or multiple day heat events (heat waves).

Based on this research, Toronto Public Health and Environment Canada adopted a new Heat-Health Alert and Emergency system commencing in the summer of 2001. The Toronto Medical Officer of Health will call either a Heat Alert or Extreme Heat Alert (formerly known as a Heat Emergency) based on the following criteria:

• Heat Alert - when Environment Canada's meteorological forecasts and results from the epidemiological study project a 65-90 per cent chance of increased mortality for Toronto residents.
• Extreme Heat Alert - when Environment Canada's meteorological forecasts and results from the epidemiological study project a greater than 90 per cent chance of increased mortality for Toronto residents.

The City of Toronto activates a Hot Weather Response Plan when a Heat Alert or Extreme Heat Alert is declared. The Plan includes the following:

• more than 750 community agencies working with vulnerable populations (i.e. elderly, ill and homeless);

• a 12-hour Red Cross operated help line to answer heat-related inquiries from the public and to respond to requests;

• homeless shelters allow people to stay inside during the day to keep cool;

• coordinated delivery of bottled water to vulnerable groups

• Emergency Medical Services respond to calls of heat-related illness and transports individuals to hospital or a cooling centre based on the health assessment of the individual;

• air-conditioned libraries and community centres are open/ available to the public

• when an Extreme Heat Alert is in effect, in addition to the above, major civic centres are operated as Cooling Centres

Information on Toronto's Hot Weather Alert system is available from the following website:
http:// www.toronto.ca/ health/ heatalerts/ heat_notification.htm

"ATMOSPHERIC HAZARDS IN ONTARIO" MAPS

Sub-Category TEMPERATURE

'DAYS WITH', 'EXTREME MAXIMUM' AND 'DATE OF LAST OCCURRENCE' TEMPERATURE DATA

Data for the 'days with', 'extreme maximum' and most recent 'date of extreme maximum' temperature graphics on this website (http:// www.hazards.ca) was extracted from Environment Canada's National Climate Data Archive. Only climate and weather observing stations with at least 20 years of temperature record during the 1971-2000 climate normals period were used in the data analyses. In some cases, stations may have been joined to extend the period of record (e.g. joining stations that may have become automated, changed station identification name and number, but still remained at essentially the same location). Not all climate stations used in the analyses are still operating. For the 'date of last occurrence' maps, stations with data records ending prior to 2000 are indicated. The 'days with' data is also available from the Environment Canada Climate Normals website (Environment Canada, 2003a):
http:// climate.weatheroffice.ec.gc.ca/ climate_normals/ index_e.html

If a station did not have 20 years of record during the 1971-2000 period, additional station selection criteria were considered in the 'extreme maximum' and most recent 'date of occurrence' analyses (Environment Canada, 2009b). This allowed additional station temperature extremes to be included. The criteria specified:

1. All extreme maximum temperature records ≥ 39°C are included if the station is a) still open as of July 2009 or b) the station was closed in 1985 or more recently. The station must also have at least 5 years of temperature record.
2. A station is included if there are 20 years or more of station period of record and a) the station is still open as of July 2009 or b) the station was closed in 1985 or more recently.

HEAT#1 - AVERAGE ANNUAL COOLING DEGREE DAYS ABOVE 18°C FOR THE PERIOD 1968-1988

This map provides Cooling Degree Day information for Ontario (Watson and MacIver, 1995). Cooling Degree Days are a measure of the amount of cooling energy which is required to maintain a residence or building at a comfortable temperature of approximately 18°C and are therefore an estimate of the air-conditioning requirements at a location. The Cooling Degree Days for a particular day are computed as the difference between the base temperature 18°C and the daily mean outdoor temperature air temperature. If the daily mean air temperature is below 18°C, there are no Cooling Degree Days for that day. The average annual total represents the average annual accumulation of Degree Days for the period 1968-1988. The map may also be considered to be an indication of the annual broad temperature pattern found within the province. This map is also available from the Integrated Mapping Assessment Project website (MacIver et al., 2000):
http:// www.can-imap.ca/ collections/ maps/ climate/ heat/ Coann5_ON.jpg

HEAT#2, #3, #4, #5 - AVERAGE NUMBER OF DAYS PER YEAR WITH MAXIMUM TEMPERATURES GREATER THAN 30°C (1971-2000)

These maps show the average annual frequency of days with maximum temperatures greater than 30°C at climate stations in Ontario (#2 provincial overview dot plot, #3 provincial overview contoured map, #4 southern Ontario, #5 northern Ontario) based on the 30 year climate normals period, 1971-2000. Only climate stations with at least 20 years of temperature record within this period were included. Some stations may no longer be in operation.

Note that a frequency less than 1 means that the event does not occur every year.

HEAT#6, #7, #8, #9 - AVERAGE NUMBER OF DAYS PER YEAR WITH MAXIMUM TEMPERATURES GREATER THAN 35°C 1971-2000)

These maps show the average annual frequency of days with maximum temperatures greater than 35°C at climate stations in Ontario (#6 provincial overview dot plot, #7 provincial overview contoured map, #8 southern Ontario, #9 northern Ontario) based on the 30 year climate normals period, 1971-2000. Only climate stations with at least 20 years of temperature record within this period were included. Some stations may no longer be in operation.

Note, for example, that a frequency of 0.2 means that a maximum temperature greater than 35°C occurs, on average, once every 5 years.

HEAT #10, #11, #12 - EXTREME RECORDED MAXIMUM TEMPERATURE

The values plotted on these maps represent the extreme maximum (or the hottest) temperature recorded at climate stations in Ontario (#10 provincial overview, #11 southern Ontario, #12 northern Ontario) over each climate station's period of record through 2008. Note that #11 is comprised of 4 individual maps that provide extreme maximum temperature information for southern Ontario:

A.Southern Ontario (overview dot plot)
and detailed temperature extreme values on maps of:
B.Southwestern Ontario
C.South Central Ontario
D.Eastern Ontario

Criteria for station inclusion in the analysis are discussed above. Some stations may no longer be in operation.

HEAT#13, #14 - MOST RECENT OCCURRENCE OF EXTREME MAXIMUM TEMPERATURE

Station locations are plotted by color code for the most recent date of occurrence of record daily maximum temperatures (#13 southern Ontario, #14 northern Ontario; the extreme maximum temperatures are plotted in Maps #10, #11 and #12). Criteria for station inclusion in the analysis are discussed above. For those locations where the record daily maximum temperature has occurred in recent years (2000-2008), the station location dots are plotted in red. Orange and blue dots indicate that the extreme maximum temperatures were recorded during the period 1990-1999 and prior to 1990, respectively. Stations where the data records end prior to 2000 are also indicated on the map with a '+' symbol. The most recent dates of occurrence (day-month-year) of extreme maximum temperatures in Ontario are listed in the EXCEL spreadsheet 'Heat-Extrememax-e.xls ', as indicated in the DATASETS summary below.

Sub-Category HUMIDEX

'DAYS WITH HUMIDEX EQUAL TO OR GREATER THAN 40', 'EXTREME HUMIDEX', 'MAXIMUM NUMBER OF CONSECUTIVE HUMIDEX DAYS' AND 'DATE OF LAST OCCURRENCE' HUMIDEX DATA (Meteorological Service of Canada-Ontario, 2006; Environment Canada, 2009b)

Hourly air temperature and dewpoint temperature was extracted from Environment Canada's National Climate Data Archive and used to calculate hourly humidex values for 36 Ontario airport observing stations over each station's period of record through 2008 (using the humidex formula defined above).

A maximum humidex on each day of the station period of record was determined, and the date of its occurrence was noted. The number of days was computed during each year when at least one hourly humidex during the day was within specific humidex threshold levels (i.e. 30-<35, 35-<40, 40-<45, 45 and greater). The annual average number of days with humidex equal to greater than 40 was calculated for each station for the recent 30-year normals period, 1971-2000, provided at least 20 years of data was available. Finally, the maximum number of consecutive days per year with at least one hourly value of humidex equal to greater than 40 was calculated and the year of its occurrence was recorded. Annual period counts of the number of consecutive days with at least one hourly value of humidex equal to or greater than 40 were also determined for each of the available stations.

Hourly temperature and/ or dewpoint data may have been missing for some dates in the station record. In these cases, a subjective analysis on the threshold range of the maximum daily humidex was made, dependent on surrounding station data information and the number and times of hours of station data missing during the day (i.e. maximum humidex is usually reached during the afternoon hours of the day, so a maximum humidex for the day would be calculated even if temperature data was missing during the overnight hours). Some stations used in the analyses had less than 20 years of data, and not all of the stations are still operating. For the 'date of last occurrence' maps, stations with data records ending in 1991 or starting after 1991 are indicated.

The results of the Meteorological Service of Canada (2006) humidex analyses are presented in HEAT Maps #15-18.

HEAT#15 - AVERAGE NUMBER OF DAYS PER YEAR WITH HUMIDEX EQUAL TO OR GREATER THAN 40 (1971-2000 AND STATION PERIOD OF RECORD)

This map shows the average annual frequency of days with at least one hourly humidex equal to or greater than 40 at hourly weather observing stations in Ontario, based on the 30 year climate normals period, 1971-2000. Only stations with temperature records greater than 20 years within this period were included. Some stations may no longer be in operation. The Ontario humidex frequency data used to generate this map is provided in the EXCEL spreadsheet 'Heat-Humidexdata-e.xls ', as indicated in the DATASETS summary below.

The humidex frequency map is interactive, returning the historical time series of the number of days during each year of the selected station's period of record through 2008 when at least one hour during the day recorded a humidex equal to or greater than 40. The bar graphics depict the annual number of days in the specific humidex "discomfort" ranges (see Environment Canada, 2002d):

• Above 45 Dangerous
• 40 - <45 Great Discomfort
• 35 - <40 Some Discomfort
• 30 - <35 Some Discomfort

(The last two ranges are only plotted for stations in northern Ontario where humidex values above 40/ 45 have not been recorded.)

HEAT#16 - EXTREME MAXIMUM HUMIDEX DURING THE STATION PERIOD OF RECORD

The values plotted on the map represent the highest hourly humidex recorded at hourly weather observing stations in Ontario over each station's period of record through 2008. As noted above, only stations reporting hourly observations of air temperature and dew point temperature were used in the humidex analyses. Stations with less than 20 years of air temperature and dewpoint temperature data for the humidex calculations are denoted with a '+' symbol. Not all stations are still in operation.

The extreme maximum humidex and its most recent date of occurrence (day-month-year) in Ontario are listed in the EXCEL spreadsheet 'Heat-Humidexdata-e.xls ', as indicated in the DATASETS summary below.

HEAT#17 - MOST RECENT OCCURRENCE OF EXTREME MAXIMUM HUMIDEX

Station locations are plotted by color code for the most recent date of occurrence of the highest recorded humidex values as determined from the humidex calculations (the extreme maximum humidex values are plotted in Map #16). As noted above, some stations had less than 20 years of record for analysis. For those locations where the record humidex has occurred in recent years (2001-2008), the station location dots are plotted in red. Orange and blue dots indicate that the extreme maximum humidex values were recorded during the period 1991-2000 and prior to 1991, respectively. Stations where the data records started after 1991 or ended in 1991 are also indicated on the map with a '+' or an 'x' symbol, respectively. Not all stations are still in operation.

The extreme maximum humidex and its most recent date of occurrence (day-month-year) in Ontario are listed in the EXCEL spreadsheet 'Heat-Humidexdata-e.xls ', as indicated in the DATASETS summary below.

HEAT#18 - MOST RECENT OCCURRENCE OF LONGEST CONSECUTIVE DAY PERIOD IN YEAR WITH HUMIDEX EQUAL TO OR GREATER THAN 40 (STATION PERIOD OF RECORD)

Station locations are plotted by color code for the most recent date of longest consecutive day period during a year with at least one hourly humidex equal to or greater than 40 on each day for the station period of record through 2008. The number plotted within the station circle is the maximum number of consecutive days with humidex equal to or greater than 40 that have occurred during a given year in the station period of record through 2008. For those locations where the greatest number of consecutive days meeting the humidex criteria has occurred in recent years (2001-2008), the station location dots are plotted in red. Green and blue dots indicate that the record occurrence occurred during the period 1991-2000 and prior to 1991, respectively. Pink dots indicate that the humidex has not exceeded 40 during the station period of record. Stations where the data records started after 1991 or ended in 1991 are also indicated on the map with a '+' or an 'x' symbol, respectively. Not all stations are still in operation.

For example, a green station circle with a number 5 indicates that a maximum number of 5 consecutive days with at least one hourly humidex equal to or greater than 40 on each day occurred during a year within the period 1991-2000.

The humidex occurrence map is interactive, returning the historical time series over the selected station's period of record through 2008 with the number of consecutive days when at least one hour during each of the days recorded a humidex equal to or greater than 40. The bar graphics are displayed for a minimum of zero occurrences during a year to the number of consecutive days for each of a maximum of five periods annually when the consecutive day equal to or greater than 40 humidex criteria was met.

The maximum number of consecutive days during a year when the 40 humidex criteria was met and the year in which it occurred at the Ontario stations are listed in the EXCEL spreadsheet 'Heat-Humidexdata-e.xls ' (see DATASETS summary below).

"ATMOSPHERIC HAZARDS IN ONTARIO" DATASETS

The four climate datasets that were used to develop HEAT Maps #2 to #18 are also available in Microsoft EXCEL spreadsheet format, as indicated below:

'Heat-Daysgreater30C-e.xls' - Ontario climate station information and average annual number of days with maximum temperatures greater than 30°C for the period 1971-2000 (HEAT Maps #2, #3, #4 and #5).

'Heat-Daysgreater35C-e.xls' - Ontario climate station information and average annual number of days with maximum temperatures greater than 35°C for the period 1971-2000 (HEAT Maps #6, #7, #8 and #9).

'Heat-Extrememax-e.xls' - Ontario climate station information, the extreme maximum temperature record and date of last occurrence through 2008 (HEAT Maps #10, #11, #12, #13 and #14).

''Heat-Humidexdata-e.xls' - Ontario hourly weather observing station information, the extreme maximum humidex record and date of last occurrence through 2008, the average number of days per year with humidex equal to or greater than 40 during the 1971-2000 period and the number of years used in the analysis, the maximum number of consecutive days during a year when the 40 humidex criteria was met and the year in which it occurred (HEAT Maps #15-18).

REFERENCES

City of Kingston, 2005. Heat Levels. http://www.cityofkingston.ca/ residents/ environment/ extreme/ heatlevels.asp

http:/ /www.kflapublichealth.ca/ Files/ Resources/ Extreme_Heat_ Health_Response_ Plan.pdf

City of Ottawa, 2009. Heat Alert Facts.
http://www.ottawa.ca/ residents/ health/ environments/ issues/ hot/ heat_alert_en.html

City of Toronto, 2009. Heat Alerts and Extreme Heat Alerts.
http:// www.toronto.ca/ health/ heatalerts /heat_notification.htm

Environment Canada, 2003a. Canadian Climate Normals 1971-2000.
http:// climate.weatheroffice.ec.gc.ca/ Welcome_e.html

Environment Canada, 2009b. Internal Data Analysis. Data Courtesy of Environment Canada's National Climate Data and Information Archive.

MacIver, D., H. Auld, A. Fenech and N. Urquizo, 2000. Integrated Mapping Assessment Project (IMAP). Developed with support from Environment Canada, Meteorological Service of Canada; the Environmental Conservation Service - Ecological Monitoring and Assessment Network (EMAN); the Great Lakes 2000 Program and The Institute of Environmental Studies, University of Toronto.
IMAP home website: http:// www.can-imap.ca and Cooling Degree Day graphic available at:
http:// www.can-imap.ca/ collections/ maps/ climate/ heat/ Coann5_ON.jpg

Meteorological Service of Canada-Ontario Region, 2005a. Internal. Data Courtesy of National Climate Data and Information Archive.

Meteorological Service of Canada-Ontario, 2006. Internal Data Analysis. Data Courtesy of Environment Canada's National Climate Data and Information Archive.

Region of Waterloo, 2003. Air Quality and your Health.
http:// www.region.waterloo.on.ca/ WEB/ health.nsf/ c56e308f49bfeb7885256abc0071ec9a/ 62f7de0d34d34d3885256bcd006355e3! OpenDocument

The Regional Municipality of Halton, 2009. Heat Alert.
http:// www.halton.ca/ cms/ one.aspx? portalId=8310& pageId=13692

Watson, B. G. and D. MacIver, 1995. Bioclimate Mapping of Ontario. Environment Canada and Ontario Ministry of Natural Resources. Summary information available at:
http:// www.can-imap.ca/ collections/ data/ climate_and_biota/ ontario_bioclimate_map.htm

DOCUMENTATION PREPARED BY:

Meteorological Service of Canada-Ontario Region, December 2003 and updated February 2007.

Revised by J. Klaassen, Meteorological Service of Canada-Ontario Region, April 2005 and updated April 2007, October 2009.