Some parts of southern Ontario have already seen the fall leaves change colour due in part to the record amount of rainfall the region experienced this summer — and it’s expected that more leaves may change colour sooner.
Global News meteorologist Ross Hull says that after the wettest summer on record for the Greater Toronto Area and other parts of southern Ontario, it appears that the excessive rainfall has “stressed certain trees,” causing an earlier leaf colour change in some areas.
“It looks like some parts of southern Ontario are already at about a 10 per cent colour change mostly outside of the GTHA — meaning the chlorophyll production is slowing down earlier than normal in some trees,” Hull said.
The rainy summer has also led to significant leaf and tree growth, added Global News meteorologist Anthony Farnell. He said often times trees will grow a certain amount in the year and then shut down photosynthesis to protect themselves for the upcoming winter.
“Trees that turn first are those that are stressed or lack certain minerals in the soil,” Farnell said.
This summer was the rainiest in Toronto history with over 500 millimetres of rain since the beginning of June, which amounts to 229 per cent of normal, Farnell said. Almost half of that rain fell on just two days — July 16 and Aug. 17 — and both caused significant flooding in the city and regions around it. Mississauga, Ont., saw a staggering 128 mm of rain in one day on Aug. 17.
However, Hull said what ultimately decides the peak colour change, the timing, and just how vibrant the foliage will be is the weather forecast in the coming weeks.
Ideally, warm, dry and sunny fall days alongside cool or crisp (but not cold) nights are the best conditions for seeing vibrant fall leaf colours, he said. Low winds also come into play so that the leaves don’t fall off the trees.
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Farnell said if there is a week of light wind and no rain, the peak gets drawn out as leaves are slow to fall but that is difficult to predict this far in advance.
“The weather will be key on how long it lasts, however, if some trees are already exhibiting a head start on their leaf colour change then that could mean an earlier peak,” Hull said.
Typically, depending on weather conditions, the leaves begin a significant change by mid-September with a peak change by Thanksgiving weekend or around mid to late October, he noted.
September has started out warm, sunny and dry but that pattern will change this weekend as temperatures drop and rain moves in. But a drier pattern appears in the forecast next week along with rising temperatures, Hull said.
The forecast is showing above-average temperatures for much of September and likely into at least early October, Hull said.
But in terms of precipitation, both Hull and Farnell noted that the outlook is a bit more uncertain.
“Hurricane season could play a role again in our weather pattern as the season is expected to become very active again later this month,” Farnell said. “It’s impossible to determine how these storms could potentially impact the region since they haven’t even developed yet.”
“Overall, another warmer than normal fall is expected around southern Ontario.”
The first official day of fall is Sept. 22.
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