Anyone who thought the fall months seemed a tad drier than usual weren’t imagining things.
According to Environment Canada, November was particularly dry and the Nanaimo region was about the driest spot on the B.C. coast.
“It has been dry. Particularly on your part of the Island,” said Doug Lundquist, Environment Canada meteorologist.
For the fall months – Environment Canada defines fall as Sept. 1 to Dec. 1 – Nanaimo only received about 60 per cent of the normal average amount of precipitation, compared to Victoria which received about 80 per cent, Vancouver at 90 per cent and Courtenay-Comox at about 70 per cent.
“You’re kind of in that dry spot there,” Lundquist said. “You got 206 millimetres in the fall and you usually get 342.”
But November was particularly dry with just 61mm of precipitation compared to the usual 197mm, less than one-third of normal.
“As we go through the fall months it keeps getting rainier, so the fact that November was that dry is really what skewed it,” Lundquist said. “It was probably, primarily, November’s fault.”
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He said a number of competing factors, such as ocean temperatures and ocean current paths, can combine to influence seasonal temperatures. One reason for the November dry spell was an off-shore high pressure ridge that deflected rain away from the Island, but Lundquist is reluctant to credit the stability of that high pressure ridge with an area of warm water temperatures, called the “bubble” or the “blob” in the Pacific Ocean.
“That’s what’s been protecting us. If we’re on the east side of the ridge we tend to be dry and the ridge was offshore, so we’re east of it and the bubble is probably because of the ridge and not the ridge because of the bubble, so I don’t think we would want to say that the bubble or the blob is resulting in this dryer pattern,” Lundquist said. “It’s not 100 per cent certain. That’s still an emerging science, so let’s just be afraid of trying to pin too much on one thing or the other.”
The city has been making sure to store water at the Jump Lake reservoir and has not had to release additional water into the Nanaimo River for salmon runs, but 2019 is trending to be the driest in 10 years, said Mike Squire, city manager of water resources.
“Just looking at it now, in our last 10 years, it’s going to be our lowest on record as far as precipitation … it’s looking that way to date. That’s the way it’s trending,” Squire said.
Flow rates for the Nanaimo River are well above the 1,400 litres-per-second minimum required for environmental considerations, such as healthy salmon runs, at about 13,000 litres per second, measured at the Trans Canada Highway bridges at Cassidy, Squire said.
He said the city’s reservoir watershed is vast and has enough yield to sustain Nanaimo for the next 10 to 20 years, but if climate change brings sustained droughts due to climate change combined with a growing population, then additional water storage will need to built, sooner than later.
“Our biggest mitigation measure for climate change impacts is impoundment storage in our watershed, for people, the environment and fish,” Squire said.
As to how much precipitation might be expected throughout this winter, Lundquist said Environment Canada can’t provide an outlook with any certainty because all it takes is one storm to significantly shift precipitation figures, but a season’s anticipated temperatures can be forecast to some degree and there is a higher probability of warmer than average temperatures, but not “over the top” for December, January and February.
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