Farmzone: Forecasts and Observations

Forecasts and Observations

Questions


Answers

  1. When is the forest fire season in Canada?

    Generally, the forest fire season in Canada runs from April through to October. The most fires and the largest areas burned happen in June, July, and August.


  2. How many forest fires occur each year?

    During a typical year there are over 9,000 forest fires in Canada, burning an average of 2.5 million hectares (ha) or 25,000 square kilometres. The number of fires and area burned can vary dramatically from year to year.


  3. What causes forest fires?

    In Canada, two-thirds of all forest fires are caused by people, while lightning causes the remaining third. This varies across the country: lightning causes over 50% of fires in western Canada and the Northwest Territories but only 10% of fires in the Maritime provinces. Despite this, lightning fires account for over 85% of the area burned in Canada, largely because many of the lightning-caused fires occur in the West and North, where there are more remote areas that are difficult to reach with fire suppression equipment. Human-caused fires usually start close to communities, where they are reported quickly and dealt with by local fire crews.


  4. How big do forest fires get?

    Most forest fires are caught in the early stages before they have chance to grow. Under extreme conditions fires can grow rapidly, sometimes exceeding 100,000 ha. In Canada, approximately 2% of forest fires account for 98% of the total area burned.


  5. Is there a way of telling if this will be a bad fire season?

    Not really. Weather forecasts are reliable for only a few days, and long-range forecasting is still unreliable. The amount of snowfall that occurs during the winter can indicate how dry the forests may be at the start of a fire season, but this usually changes after the spring rains.


  6. How fast do forest fires burn?

    Most forest fires advance at a rate of less than 0.5 km/h, and few spread faster than 1 km/h. The fastest forest fires can burn at 6 km/h or more.

    The speed that a fire burns depends on the type of trees and the amount of moisture in the forest. Coniferous (evergreen) trees burn 5 to 10 times faster than deciduous trees because of the resin in the bark and needles. Deciduous trees are more resistant to fire when the leaves are out.


  7. How much heat comes off a fire?

    As with the speed of a fire, the intensity of a fire depends on the type of trees and the amount of moisture in the forest. An average surface fire on the forest floor might have flames reaching 1 metre in height and can reach temperatures of 800°C or more. Under extreme conditions a fire can give off 10,000 kilowatts or more per metre of fire front. This would mean flame heights of 50 metres or more and flame temperatures exceeding 1200°C.


  8. What about all that smoke?

    Smoke rises from a fire in a plume consisting of liquids, gases, and particles of different sizes. The small particles in smoke, and ozone produced by the reaction of sunlight with gases in the plume, can easily pass through our noses into our lungs and cause health problems in children, the elderly, and people with heart or lung conditions.

    The spread of smoke is affected by a combination of wind and air temperature. Dense smoke occurs when the winds are calm and the surface air temperature is cooler than the air above it, but when the air is unstable and windy, smoke can be carried thousand of metres up in the atmosphere or downwind from the fire. Weather features may even trap smoke in areas far from a forest fire, while regions close to the fire will have little smoke.


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