Bushfires & Back Burning

Bushfires and their impacts is something you can’t avoid when living in Australia. It is not uncommon that you wake up and the air is full of smoke. Last year we had to evacuate a campground in a national park in the middle of the night due to an approaching bushfire.

Meanwhile, the present drought conditions not only foreshadow a serious bushfire season, but this year’s bushfire season has already started earlier than expected. Just recently we experienced devastating bushfires close to the Gold Coast.

But often, especially in the cooler months, the smoke is caused by hazard reduction burning, which is conducted to reduce fuel build-up and decrease the likelihood of serious hotter fires.

So what is hazard reduction burning and what causes all the bushfires? And what is back burning?

Hazard Reduction (Burning)

Hazard reduction generally is any activity that reduces or removes fuel before the onset of a bushfire, to minimize damage to life, property and the environment if a bushfire does occur.

Methods of hazard reduction include

• Hand clearing (e.g. raking up leaves, clippings, clearing out gutters),
• mechanical clearing (e.g. mowing, slashing, ploughing, bulldozing, grading) or
• controlled burning (hazard reduction burning).

Generally in Australia, land managers and owners are responsible for conducting hazard reduction to protect existing dwellings, major buildings or other assets susceptible to fire.

Double fuel means a quadruple the fire intensity

Research has found that doubling the fuel in the forest will double the rate of spread and quadruple the fire intensity. Consequently, removal of fuel might be the solution.

Although complete removal of fuel means an area will no longer support fire, such a practice may be harmful to the environment. The more common practice is to reduce the amount of fuel, in which case the fire would

• generate less heat and be less dangerous for firefighters and the general public
• travel more slowly
• have a lower flame height and be less likely to develop into a crown fire
• be less likely to produce embers that cause spot fires.

In many circumstances, hand and mechanical clearing methods will be considered first as they could be the best way to protect assets. These methods can be safer than burning, easier to organize and maintain.

Hazard Reduction burning is an important part of preparing for bush fires, and is well embedded as part of fire protection systems throughout Australia. It should only involve experienced landholders or qualified firefighters to ensure the fire does not escape and the operation is carried out safely.

Before starting a hazard reduction burn, fire agencies and land managers consider weather forecasts and conditions and the impact on the environment and the local community.

Hazard reduction burning not always achieves the desired result

But does the burning actually reduce the fuel in the forest to the desired levels and will the reduction in fuel levels achieve the aim of being able to control bush fires? Fuel reduction burns will not necessarily halt the spread of bush fires.

While it is intended that fuel reduction burns will be successful in reducing fuel levels with the minimum of damage to the forest, this is not always the case.

Post burn assessments of the effectiveness of prescribed burns in the Blue Mountains in the period 1990 to 97 found that 30 per cent of the burns had a negative result, 40 per cent were sub-optimal, and 30 per cent could be rated as effective burns. The negative results occurred when there was more “creation of fuel” than reduction of fuel, with “creation” of fuel being the fire’s curing of fuels rather than consumption of them.

While hazard reduction burning is the principal means to reduce the risks of bushfire, it should not be applied uniformly. To be effective it needs to be designed to be applied to specific vegetation types and implemented by properly trained and resourced staff.

Side effect: hazardous air pollution

A serious side effect is smoke pollution, which can briefly fumigate nearby communities. Prolonged spells of hazardous air pollution “can affect everyone’s health”. The smoke is composed of combustion products i.e. carbon dioxide, carbon monoxide, water vapor, particulate matter, organic chemicals, nitrogen oxides and other compounds. The principal health concern is the inhalation of particulate matter and carbon monoxide.

Since any fuel reduction burning operation runs the risk of escaping control and causing a bushfire, sometimes hazard reduction burns get out of control. And then is becomes as wildfire …

Bushfires (Wildfires)

The Australian climate is generally hot, dry and prone to drought. The non-profit Climate Council reported that Global warming is increasing the frequency and severity of wildfires.

At any time of the year, some parts of Australia are susceptible to bushfires. The widely varied fire seasons are reflected in the continent’s different weather patterns. A website of the Australian Government shows the fires currently burning.

For most of southern Australia, the danger period is summer and autumn. For New South Wales and southern Queensland, the peak risk usually occurs in spring and early summer. The Northern Territory experiences most of its fires in winter and spring.

A wildfire is an uncontrolled fire, which can also be classified more specifically as e.g. a bushfire, desert fire, forest fire, grass fire or vegetation fire.

Grass fires frequently occur after good periods of rainfall which result in abundant growth that dries out in hot weather. Bushfires tend to occur when light and heavy fuel loads in Eucalypt forests have dried out, usually following periods of low rainfall.

The basic factors which determine whether a bushfire will occur include the presence of fuel, oxygen and an ignition source. The fire intensity and speed at which a bushfire spreads will depend on ambient temperature, fuel load, fuel moisture, wind speed and slope angle. E.g. the rate of spread of a fire doubles with every ten degrees of increase in slope.

The causes of bushfires

There are two basic causes of wildfires in Australia. One is natural (lightning) and the other is people. The most common direct human causes of wildfire ignition are:

• Arcing from overhead power lines
• Arson
• Accidental ignition in the course of agricultural clearing, grinding and welding activities
• Campfires
• Cigarettes and dropped matches
• Sparks from machinery
• Controlled burn escapes.

Above all, sometimes even the Police is causing fires by parking their patrol-car in dry grass – yes one should not do that …

Fire Danger Rating (FDR)

In Australia there is a standardized Fire Danger Rating (FDR). During the fire season the Bureau of Meteorology (BOM) provides fire weather forecasts. Fire agencies determine the appropriate Fire Danger Rating by considering the predicted weather including temperature, relative humidity, wind speed and dryness of vegetation.

The different fire & emergency services of the states inform on the internet in a timely manner about the current bush fires and the associated dangers:

• New South Wales: Fires Near me
• Northern Territory: Fire Incident Map
• Queensland: Current Bushfires
• South Australia: Warnings and incidents
• Tasmania: Tasmanian Fire Service
• Victoria: Vic Emergency
• Western Australia: Emergency WA

Injuries and fatalities

In the years between 1967 and 2013, major Australian bushfires have resulted in over 8000 injuries and 433 fatalities, close to 50 per cent of all deaths from major Australian natural disasters in the period (excluding heatwaves). Over this same period, bushfires cost approximately A$4.7 billion.

Risk Frontiers has estimated that nearly 1 million addresses in Australia are located less than 100 metres from bushland, putting them at the highest risk from bushfires.

If you want to know more about bushfires, I recommend a very good website by the Australian Academy of Science: Understanding bushfires.

Furthermore the Bushfire Mythbusting Guide by the Australian Climate Council is worth to read.

Back burning

The difference between hazard-reduction burning and back burning is effectively the same as the difference between elective and emergency surgery.

Back burning is a last-resort measure to stop wildfire from burning out specific areas. It works by setting fires from containment lines, such as established fire breaks or hastily contrasted ones made with a bulldozer or cut by hand.

It is called back burning because the small fires are designed to “burn back” towards the main fire front and are usually burning and travelling against ground level winds.

The ecological impacts of back burning are rarely discussed but may be quite substantial. Wildlife, which can normally flee a fire front, can become trapped between the bushfire and the back burn. Exacerbating impacts on wildlife is the technique known as “blacking out”. It involves setting fire to unburnt areas that escaped combustion by the back burn. Such unburnt patches can be critical refuges for wildlife and a sort of seed for recovery of adjacent burnt areas.