Geography of Toronto

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Toronto's skyline from its harbour

The city of Toronto, Canada, covers an area of 630 km2 (243 sq mi) and is bounded by Lake Ontario to the south, Etobicoke Creek and Highway 427 to the west, Steeles Avenue to the north, and the Rouge River to the east. In addition to Etobicoke Creek and the Rouge River, the city is trisected by two minor rivers and their tributaries, the Humber River in the west end and the Don River east of downtown. Both flow southward to Lake Ontario at Humber Bay and Toronto Harbour respectively, which are part of the longer Waterfront. The concentration and protection of Toronto's ravines allows for large tracts of densely forested valleys with recreational trails within the city. 17.5% of Toronto is covered with trees,[1] a fairly high percentage within a large city in North America and there are ambitious proposals to double the coverage.

Scarborough Bluffs

The shoreline of the former Lake Iroquois is a major west−east geological feature which was formed at the end of the last glacial period. In the west end, Davenport Road follows the ancient shoreline with the steps to Casa Loma rising above and downtown skyscrapers clearly visible to the southeast. It merges with current Lake Ontario shoreline at the Scarborough Bluffs promontory.

Toronto's immediate neighbours are Mississauga and Brampton within the Regional Municipality of Peel, Vaughan and Markham within the Regional Municipality of York, and Pickering within the Regional Municipality of Durham. The Greater Toronto Area (GTA) includes the regional municipalities of Halton, Peel, York and Durham.

The GTA is part of a larger, natural ecosystem known as the Greater Toronto Bioregion. This ecosystem is bounded by Lake Ontario, the Niagara Escarpment, and the Oak Ridges Moraine, and includes many watersheds that drain into Lake Ontario. Some parts of Toronto, such as High Park and the lower Humber River are located in the most northern parts of the Carolinian forest zone found in North America.

In March 2005, the Government of Ontario unveiled the boundaries of a greenbelt around the Greater Toronto Area, a 7,200 km2 (2,800 sq mi) area stretching from Niagara Falls to Peterborough. The green belt is designed to curb urban sprawl and to preserve valuable natural areas and farmland surrounding the city. However, some types of development including detached single residential, quarries and commercial facilities continue to get approved, exerting pressure and population growth on the Greenbelt. Toronto is the latest in a line of cities that have implemented growth boundaries of some kind as a method of restricting urban growth, including Ottawa, Portland, Oregon, Frankfurt, Melbourne, Seoul and London, UK.

Climate[edit]

Toronto
Climate chart (explanation)
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Average max. and min. temperatures in °C
Precipitation totals in mm
Source: Environment Canada

Toronto's continental climate is moderated by Lake Ontario; its climate is among the mildest in Canada east of the Rocky Mountains. Downtown Toronto sits in a pocket of the humid continental climate (Köppen climate classification Dfa) zone found at the south-western end of Lake Ontario covering the southern part of the city - including downtown, where the annual average temperature exceeds 9 °C (48 °F). It is located in hardiness zone 6a.[2] There is a high degree of variability from year to year and sometimes even over a period of days, particularly during the winter months.

Lake Ontario's water temperature varies due to upwelling of colder water or warmer pools of surface water creating very localized thermal contrast; the deeper waters of the lake, far from the shore, remain at a near constant water temperature of 4 °C (39 °F), the effect of which is either cooling or warming (in winter). This creates generally warmer nights through the colder season. When offshore winds occur in summer, they warm as they blow toward the lakeshore in the evening; conversely, the cooling effect by the lake is most pronounced on spring afternoons, which affects Toronto even more than other cities on the Great Lakes as during spring onshore east to southeast winds are predominant, on some days the temperatures can be as much as 10C cooler than areas located far enough away from the Lake Ontario, an effect that wanes by summer when the dominant windflow becomes more southwesterly.

Springs and autumns feature varied weather with alternating periods of dry, sunny weather and rain. These seasons are brief when compared to summer or winter seasons, many days in thse seasons are sunny with pleasant rather than warm or cold temperatures. Nights are generally cool, but frosts are rare. Snow can fall in early spring or late fall but usually melts quickly after contact with the ground. At these times changeable times of the year, temperature contrasts (up to 30 °C (54 °F) in extreme cases) can occur within a short time frame due to rapidly changing air masses that sweep across the continent, Toronto's weather is affected by the relative position of the polar jet stream and storm track, both of which pass over the area with some frequency.

Annual average precipitation is 831 mm (32.72 in).

Winter and snowfall[edit]

Despite being cold, extended snow free periods occur in most winter seasons and precipitation can be rainfall with temperatures sometimes climbing above 10 °C (50 °F). Average winter snowfall is 121.5 cm (47.8 in) at the weather station in Downtown Toronto[3] and 108.5 cm (42.72 in) at the airport.[4]

The average January maximum/minimum is −1 °C (30 °F)/−7 °C (19 °F) in the city.[3] There are usually a few colder periods where temperatures remain below −10 °C (14 °F) and less frequently below −20 °C (−4 °F) at night (especially in the northern suburbs), with wind chills making it feel like −30.[5]

Due to its position on the northwest shore of Lake Ontario, Toronto is not a direct target of heavy, wind−whipped lake-effect snow squalls that hit other Great Lake cities on the south/east shorelines of the lakes, in areas where prevailing winds amplify lake effect. Despite this, there are usually two or more heavy snowfalls each winter which deposit at least 15 cm (5.91 in) accumulation, usually from powerful winter storms known as "Colorado Low"s or Panhandle Hooks that pick up moisture en route to the Great Lakes. These storms can produce strong easterly driven winds that fetch additional moisture from Lake Ontario. They frequently come with a volatile mix of snow, ice pellets, freezing rain and sometimes just ordinary rain, all of which can disrupt transportation, and in severe cases, interrupt power supply. A sustained freezing rain event occurred on December 22, 2013 plunging 30% of the city into darkness, some until after Christmas Day [6]

Such storms can also produce large snowfall amounts, higher totals found in areas closer to Lake Ontario, sometimes falling over a series of days or weeks creating havoc. On January 13, 1999, former Toronto mayor Mel Lastman called in the Canadian Forces to assist with snow removal and clearing streets. Within twelve days, the downtown Toronto weather station at the University of Toronto (Trinity College near Queens Park) recorded an average season's worth of 118.4 cm (46.6 in) of snow, much of it lake effect from Lake Ontario and a monthly record for January, but fell short of the snowiest month overall March 1870, with 158.5 cm (62.4 in), of which 89 cm (35.0 in) fell over a 5-day span. February 2008 set a record a snowfall record for the month with 76.8 cm (30.2 in) falling at the airport. The winter of 2007−08 brought accumulated seasonal snowfall totals of 209.7 cm (82.6 in) downtown and 194.0 cm (76.4 in) at the airport. The heavy winter snows, in combination with record rains during June–July of that year made 2008 the wettest year on the climate record with over 1,070 mm (42.1 in) of total precipitation.

On the opposite extreme, the winter of 2011-12 had the lowest seasonal snowfall total with 41.0 cm (16.1 in). March 2012 was the warmest March on record. The least snowfall in a calendar year was 2006, with only 32.4 cm (12.8 in). The El Nino influenced winter of 2009-10 had 52.4 cm (20.6 in), March 2010 recorded no measurable snow, the first such occurrence in any March since 1946, this was followed by the warmest April ever on record.[7]

Toronto skyline taken from Colonel Samuel Smith Park in Etobicoke.

Summer[edit]

Maximum temperatures typically range from 23 to 31 °C (73 to 88 °F) with moderate to high humidity, proximity to Lake Ontario and the other lakes contribute to summer moisture content but far away sources like the Gulf of Mexico also factor in. Temperatures over 32 °C (90 °F) occur but usually no longer than over a period of a few days and they very rarely exceed 38 °C (100 °F). Night temperatures generally hover close to 20 °C (68 °F) in the city but during hotter spells can remain closer to 25 °C (77 °F). Summer heat episodes are usually broken by cooler, drier periods not experienced further south on the continent. But intense heat episodes pose a health risk to some as they often arrive with high humidity and dangerous levels of airborne smog. Summer thunderstorms are a regular occurrence and can pop up quickly, especially west and north of the city in areas more prone to the "lake breeze front" or "lake breeze thunderstorms" phenomenon, in which intense, sharply defined squall lines develop quickly on summer afternoons amplified by localized wind patterns between the Great Lakes.[8] These storms sometimes move into the city causing localized flooding, intense lightning and severe winds knocking down trees and powerlines.

Severe weather and records[edit]

In addition to snowstorms, ice storms, windstorms and heavy rainfall events associated with Tropical storms, very severe thunderstorms or tornadoes are rare, but do occur. Tornado warnings have been posted for the city on a few occasions in the past few years, however no touchdowns have been confirmed in the city since a weak tornado hit Scarborough in the mid−1990s. A pair of dangerous F2 tornados did touchdown in neighbouring Vaughan on August 20 during the 2009 tornado season.

The tropical storm remnant of Hurricane Hazel caused 81 deaths in October 1954 due to flooding that swept homes along river banks into Lake Ontario. A sudden downburst during a strong thunderstorm was believed to have played a contributing factor in the Air France Flight 358 crash in August 2005 and just a few weeks later record-breaking intense rainfall, the worst since Hazel, deluged north-central sections of the city within a couple of hours resulting in record insurance claims. Some rain guauges recorded 175mm (7") of rain, over 100mm (4") in just one hour. Another large rainstorm with intense, record rainfall amounts struck a wide swath of the city during the afternoon rush hour on July 8, 2013 flooding city streets, subway tunnels, basements and knocking out power for over 2 million residents, stranding commuters, some that had to be rescued from a submerged train. A daily rainfall record of 126.4mm (5") was set at Pearson Airport, most falling in an hour and a half. Flood insurance claims are likely to exceed the 2005 storm due to a wider area affected.[9]

During the 1936 North American heat wave, downtown temperatures in Toronto exceeded 40 °C (104 °F) on three consecutive days (July 8−July 10),[10] an unofficial all-time record high.[11] The city was ill equipped at that time to handle such a prolonged extreme heat wave, and heat stroke claimed 225 lives in the city,[12] not counting indirect deaths from causes such as drowning.[13] The hottest month recorded, however, was July 1921, when the average maximum temperature downtown was 31.7 °C (89 °F), and a mean temperature of 26 °C (79 °F) still holds as the warmest month. At the airport, the highest monthly maximum average was 31.2 °C (88 °F) in July 1955.

The coldest minimum temperature of −33 °C (−27 °F) was recorded on January 10, 1859. The coldest temperature recorded at Toronto Pearson International Airport was −31.3 °C (−24.3 °F) on January 4, 1981, and the coldest windchill recorded was −44.7 on the same day.[4][5] The coldest month overall: at the airport January 1994, averaging −12.4 °C (10 °F); downtown February 1875 averaged −12.6 °C (9 °F). Winter cold snaps pose a danger as they often come with high winds, leaving the city's homeless population very prone to frostbite and hypothermia.

Upward temperature trend[edit]

Based on public records provided by Environment Canada, the average annual temperature has increased 1.5 °C (2.7 °F) at Pearson Airport over the last decade as compared to the thirty−year normals from 1971−2000, more of this increase occurred at night: the average minimum temperature was 1.9 °C (3.4 °F) higher last decade. Average precipitation during the same period was close to the average of the previous period, snowfall totals down only marginally with slightly higher rainfall. By month in order, the largest mean temperature increases occurred in September, August, January, April and November while only a marginal average increase was observed for May. Part of this warming is likely attributed to increased urban growth surrounding the airport.

An older study conducted in the 1990s analysed the heat island effect comparing data from selected regional stations, including both Downtown Toronto and Pearson Airport.[14]

The table below is preliminary average temperature data for the last decade provided by Environment Canada's climate database. It might be noted that the decades between the 1930-1950s were warmer in Toronto than the period from the 1960s through to the first half of the 1990s, a large part of the latter timespan is included in the 1971-2000 climate averages.

Toronto Pearson Airport
Climate chart (explanation)
J F M A M J J A S O N D
 
 
47
 
−1
−8
 
 
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15
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−5
Average max. and min. temperatures in °C
Precipitation totals in mm
Source: Environment Canada

Statistics[edit]


References[edit]

  1. ^ Trees on Private Property
  2. ^ "Plant Hardiness Data". Natural Resources Canada. December 19, 2011. Retrieved February 23, 2013. 
  3. ^ a b c "1981 to 2010 Canadian Climate Normals". Environment Canada. 2014-02-13. Climate ID: 6158350. Retrieved February 24, 2014. 
  4. ^ a b c "Toronto Lester B. Pearson INT'L A". 1981-2010 Canadian Climate Normals. Environment Canada. Retrieved June 3, 2014. 
  5. ^ a b "Canada's Wind Chill Index". Environment Canada. 2005-01-04. Retrieved 2009-02-16. "The wind chill is expressed in temperature-like units, but because it is not the actual air temperature, it is given without the degree sign." 
  6. ^ [1]
  7. ^ Ontario Weather Review
  8. ^ Lake Breeze Weather
  9. ^ "TO Flood by he Numbers". CTV News. 
  10. ^ "Daily Data Report for July 1936 (station in University of Toronto)". National Climate Data and Information Archive. Retrieved 21 June 2012. 
  11. ^ Woods, Michael (21 July 2011). "When is a temperature record not really a temperature record?". Toronto Star. Retrieved 21 June 2012. 
  12. ^ Phillips, David. "Heat Wave". The Canadian Encyclopedia. The Historica-Dominion Institute. Retrieved 21 June 2012. 
  13. ^ Wencer, David (16 November 2011). "The 1936 Heat Wave". Heritage Toronto. Retrieved 21 June 2012. 
  14. ^ Impact of urbanization on the climate of Toronto, Ontario, Canada
  15. ^ "Daily Data and Monthly Data for Toronto Lester B. Pearson Int'L A". Environment Canada. Retrieved January 15, 2013. 
  16. ^ [http://www.climate.weatheroffice.gc.ca/climateData/dailydata_e.html?timeframe=2&Prov=ONT&StationID=31688&hlyRange=2002-06-04 %7C2013-01-14&Month=12&Year=2012&cmdB2=Go&Day=1 "Daily Data and Monthly Data for Toronto City"]. Environment Canada. Retrieved January 15, 2013. 
  17. ^ Daily Data for Toronto, accessed 28 March 2012.
  18. ^ "Canadian Climate Normals 1971-2000, Toronto Pearson International Airport". Environment Canada. 
  19. ^ Climate data for Toronto Lester B. Pearson Int'l, ON, Canada, accessed 25 March 2012.
  20. ^ "Toronto, Ontario". Canadian Climate Normals 1971–2000 (in English & French). Environment Canada. Retrieved June 22, 2013. 
  21. ^ "Toronto Lester B. Pearson INT'L A". Canadian Climate Normals 1981–2010. Environment Canada. Retrieved June 3, 2014.