Now that camping season has arrived, many residents are watching fire warnings to know where they can start a fire.
At the May 1 regular council meeting, council received education from Tom Thompson, Drayton Valley/Brazeau County Fire Services Chief, on how to calculate these warnings for the area.
“Since it's fire season, we're getting a lot of questions wondering why we have different bans at different times,” Thompson said.
The Fire Weather Index is what departments use to calculate different levels of fire warnings, Thompson says. He says this model is used across the country and consists of several different factors: the fine fuel moisture code, the duff moisture code, the drought code, the initial spread index, the accumulation index, and the fire weather index.
“It's based on data that Alberta Forestry collects on a daily basis,” Thompson said.
He said that these different factors all depend on the readings in a particular area. Since the topography of each region can vary, the level of fire warnings can also vary from county to county.
The exact fuel moisture code depends on how dry the grass is, Thompson said. “It only takes about 0.6 millimeters to change that rating,” Thompson said.
He says that if he gets a rating of 80 or higher, he will support free burning. At 90 or higher, there is a possibility that it will ignite and cause spot fires throughout the area.
The DAF moisture symbol focuses on the topsoil on the ground, such as dead or decaying woody material. He said this layer could easily ignite if it was dry enough. Anything with a rating over 20 can support ignition and sustained burning.
The average amount of moisture found deep in the ground forms the basis of the drought code. Thompson says that number will determine how deep the fire is in the ground.
“That's a concern for us since that's where we have problems where the roots will burn at the bottom of the tree,” Thompson said. “You end up with what's called 'widow-making trees' where all the roots underneath get burned, and then the tree, if there's any wind, falls on the firefighters or anyone else around it.”
The rating of 15 is low, and the land is largely waterlogged, he said. Anything at 300 or higher will keep burning for a long time.
Primary spread index that includes wind speed and fine fuel. He said it does not take into account different types of fuel, but only the grass in the area. A rating of 10 or higher will cause rapid spread and will have the ability to ignite candles, with the fire reaching the treetops.
The total amount of fuel available for burning is calculated using the accumulation index.
“You take the DAF wetness code and the dryness code together and you create a classification,” Thompson said.
A rating of 60 or higher is a concern because this type of fire is difficult to extinguish.
The fire weather index is the one most firefighters will generally talk about, Thompson says.
He said that it indicates the intensity with which the fire will burn and depends on the initial spread index and the accumulation index.
All of these different factors combine to form one number called head fire severity, Thompson said. Last year, with the Buck Creek Fire, the HFI was at level six, which is the worst it could be, he said.
He said conditions in the area last year set the stage for the perfect storm. All indicators were high, which is why it was difficult to extinguish the fires.
Alberta Forestry prepares daily reports for municipalities, and that's what those areas base their fire warnings on, Thompson said. He says if they see that any of these numbers are in the red zone for more than a few days, they will change the warning for the area.
“Some people think we're pulling this out of the air,” Thompson said. “This is not the case. We look at this every day and take general trends [into consideration]”.
One day of low numbers doesn't make a difference, but he said if there are multiple days of low numbers, the warning could be lowered.
The Fire Weather Index map can be found at www.alberta.ca/fire-danger.
Amanda Jeffrey, Local Journalism Initiative Reporter, Drayton Valley and District Free Press
