The kinds of floods that triggered mudslides and threatened northern communities this past spring could become much more frequent as a result of British Columbia's unprecedented mountain pine beetle epidemic, community leaders were told yesterday.
And if floods weren't enough to worry about, cities and towns in beetle-hit areas also face a fire threat from beetle-killed timber that, if left standing, could quickly turn into an inferno.
"What we've seen over the last few years is that transition from the ground fire up into the crown seems to be moving pretty quickly," Chris Duffy, superintendent of fuel management with the B.C. Ministry of Forests, said in describing fires in forests killed by the pine beetle.
The fires behave "almost like a large grassfire," Mr. Duffy added, resulting in less time to evacuate residents or move in firefighting crews and equipment.
Mr. Duffy spoke at a panel on community safety at a pine beetle conference held as part of the Union of British Columbia Municipalities Convention in Vancouver this week.
He urged community leaders to develop fire-management and "fuel control" plans, saying such measures can make control measures more effective.
On the flood side of the equation, the pine beetle outbreak can affect water and snow levels in several ways, said Jim Whyte, director of operations for the Provincial Emergency Program.
Dead trees don't hold as much snow in their branches, resulting in up to 30 per cent more snow left on the ground to melt.
More sun can make its way to the ground through bare trees than through needle-covered limbs, so snow melts earlier and faster.
Faster water flows can erode riverbanks, compounding the problem.
Studies of small watersheds suggest beetle outbreaks could lead to water flows that were typically seen once every 50 years coming around every five years - resulting in significantly higher costs for disaster response and flood control, Mr. Whyte said.
"It's going to mean additional costs for government, no question," he said after his presentation. "You can't have those kinds of flood frequencies without it costing you more money."
It's not definitively known what impact the pine beetle outbreak would have on big watersheds such as the Upper Fraser, Mr. Whyte said, adding that efforts are under way to predict changes in water and snow levels that could result from huge areas of dead and dying trees.
But for an indication, consider what happened this past spring, when the Nechako and Fraser Rivers both had extremely heavy snow packs, he said.
The Nechako watershed has suffered tremendous tree loss from the pine beetle, whereas the Upper Fraser watershed has not been heavily affected, Mr. Whyte said.
In similar weather conditions, Fraser River levels hit one-in-20-year highs, whereas the Nechako River recorded eight consecutive weeks of one-in-50-year levels, Mr. Whyte said - conditions that would have been much worse had it not been for flood-control measures taken on the Nechako system.
Not all of the differences in the two river systems can be chalked up to the pine beetle outbreak, he said, but a "substantial" amount of the difference can be attributed to beetle-influenced runoff in the Nechako region. Such changes are likely to be long-standing.
"These are things that are going to endure for 30 to 60 years," Mr. Whyte said. "It's going to be a long time before forest cover is restored in these watersheds."
He said the provincial and federal governments should work together on dike programs.
During his speech, he also urged community leaders to take flood risks into account when planning and building new developments.
The pine beetle conference featured speakers from communities, aboriginal and government agencies. The UBCM convention continues this week.