Toronto residents are being urged to water vulnerable trees after the longest string of rainless days in 47 years.
A trace amount of rain - less than 0.2 millimetres - fell on Toronto on Friday morning after 18 straight days without any precipitation. The city has had only three longer unbroken dry spells since records have been kept at Pearson Airport: A 26-day spell in 1938, followed by two 21-day droughts in 1957 and 1963.
"This is a milestone of sorts," said Environment Canada senior climatologist David Phillips, noting how much has changed from the cold, cloudy months of June, July and August that made this summer the fifth wettest on record.
"It was like the faucet was on and then it was turned off."
The wild weather swing can be attributed to the jet stream - the narrow wind current that separates cold air to the north and warm air to the south. For most of the summer, it was parked south of the Great Lakes, when it usually runs across Canada's North. Now it is where it should have been in the summer, Mr. Phillips said.
September is usually the wettest month of the year, making this dry spell particularly unusual, he added. Toronto received about 50 per cent more sunshine than usual in the first 17 days of the month. "I've heard people say to me, 'Isn't that nice. The bummer of a summer and now we're getting the summer when vacations are over and the kids have gone back to school.' It's like salt in the wound, like nature kind of laughing at us," he said. "But other people are saying better late than never."
It was a boffo summer for the city's tree canopy, as rain and low cool temperatures allowed saplings and shrubs to establish solid root systems, said Richard Ubbens, director of Toronto Urban Forestry.
But because trees still appear lush , "watering is not on anybody's radar," even though the roots are drying out with so little rain.
"We're losing that [summer]benefit now because the soil is so dry that all of the new roots will die off. That just means we'll be starting off with stressed trees again in the spring," he said.
Trees under three years old are especially vulnerable and require 20 litres (about two pails) of water a day. Mature trees should get a soaking once every seven to 10 days.
Rhonda Teitel-Payne, urban agriculture manager for the Stop Community Food Centre, said the dry spell will have "a huge impact" on community gardens without water access. But the sunny skies of late have been a blessing for the agency's 8,000-square-foot irrigated garden at Earlscourt Park after a summer of difficult growing conditions.
Tomatoes, which are a staple for the charity because so many different cultures use them, were a problem.
"Our seedlings got off to such a slow start," she said. "It took a long, long time to get them to flower and start bearing fruit."
Longest dry spells with no trace of rain recorded at Pearson Airport:
26 days - Sept. 23 to Oct. 18, 1938
21 days - Sept. 25 to Oct. 15, 1957
21 days - Oct. 4 to Oct. 24, 1963
18 days - May 29 to June 15, 1949
18 days - June 21 to July 9, 1963
18 days - Aug. 31 to Sept. 17, 2009
Average rainfall for a Toronto summer: 228.2 millimetres
Rainfall this summer: 299 millimetres
Average rainfall for September: 77.5 millimetres
Rainfall so far this September: 0 millimetres
Average hours of sunshine for the first 17 days of September: 118
Hours of sunshine for the first 17 days of this September: 173
Source: Environment Canada senior climatologist David Phillips