Island droughts are going to worsen, researchers say


Vancouver Island droughts will be worse in coming decades than they have been in the past 350 years, University of Victoria researchers say.

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A study found that natural droughts from past centuries were more severe than initially believed. Climate change and deforestation will only aggravate conditions that have already seen streams dry up and wildfires rage, research associate Bethany Coulthard said.

Looking at tree-ring data for coastal areas in southern B.C., the report found that 16 historical droughts dating back to the 17th century were more serious than what was recorded. Previous data depended on stream flow, collected at measurement stations in low-flow rivers.

“Those 16 droughts are what we’re calling natural droughts. They’re driven by normal climate variations,” Coulthard said.

“But what we couldn’t account for in the model was anthropogenic climate change and land-use changes like deforestation. When you combine those with these natural droughts that were worse than we thought, that’s where we can expect to see worse droughts in coming decades.”

The researchers focused on two types of trees: One with rings sensitive to winter snowpack and another with rings sensitive to summer drought conditions. They tell a more complete story than stream data, Coulthard said.

“They can tell you the story of drought in every year going back,” she said.

Victoria and the southeastern side of the south Island are in the ecological zone called Dry Douglas Fir, said geographer Dan Smith, who leads the UVic Tree Ring Laboratory.

“We are naturally dry,” he said. “We are in the rain shadow of the Olympic Mountains and the Vancouver Island ranges — the spine of the Island, top to bottom.”

The report, published in the Journal of Hydrology and on, is co-authored by Smith and David Meko of the University of Arizona.

Coulthard will meet provincial planners next month to discuss the modelling.

“This is an important time with communities and the province to know that we need to be more conservative about our drought mitigation strategies,” she said.

While humans can adapt by bringing in water from elsewhere, she said species such as salmon are especially vulnerable.

“In terms of stream ecology and local Pacific salmon, they cannot adapt. Obviously, they’ve survived droughts in the past, but they haven’t had to face climate change and land-use change. This could have disastrous impacts for salmon and stream ecology.”

Langford fire chief Bob Beckett said the department takes forecasting into account. It is organizing a workshop for firefighters on preparedness this month. “The focus is going to be on what are the trends, what are the forecasts. Why do we need to re-evaluate going about fighting our fires and what are the risks and how can we be more proactive in promoting the Firesmart [wildfire education] program?” Beckett said.

Kevin Skrepnek, chief information officer for the B.C. Wildfire Service, said planners take predictive models into account for areas such as staffing and preparedness. “Our people are aware of [reports], we’re aware of the predictive shifts of what may happen to forests on the coast,” he said. “We shift resources around on a day-to-day basis.”

— with a file from Katherine Dedyna

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