How Weather Patterns Affect The Incidence Of Fire

Weather patterns have a direct effect on the incidence of fires. This is exemplified in the varied fire seasons in different parts of Australia. In Northern Australia, there are more fires during the winter and spring. In New South Wales and southern Queensland, the occurrence of fire is heightened during spring and early summer, and for the majority of southern Australia, peak fire season is during summer and autumn.

Weather conditions that contribute to the risk of fire are lack of rain, high winds, and low relative humidity. High temperatures and the heat of the sun dry wood and grass, causing these to burn readily. Hot air decreases the moisture content of grasslands and forests, causing fire, when it occurs, to spread speedily.

Very little rainfall results in parched plant life, dead twigs and dry leaves, providing abundant fuel for fire. In times of drought or combined with hot, windy weather, even large logs, smaller branches of trees, and green leaves can become flammable.

Wind supplies a copious amount of oxygen to keep fires burning. Higher winds equals more oxygen equals more intense flames. If the speed of the wind doubles, the rate of fire spread quadruples. Winds also carry embers to wherever they’re blowing, thus starting more fires. This phenomenon is termed as spotting.

Low humidity levels also increases fire risk. The moisture in the air is measured in terms of relative humidity. Relative humidity is defined as the ratio of the amount of water in the air at a given temperature to the maximum amount it can hold at that temperature. It is expressed as a percentage. So a percentage of less than 20% of relative humidity is cause for concern because at this rate, fuels dry out and become more flammable.

The Bureau of Meteorology broadcasts fire weather warnings when fire conditions are prevalent. Bush fires are more likely to extend quickly when the weather is hot, dry and windy. To reduce the risk of fires damaging or destroying life and property, many states and territories issue total fire bans on days of extreme fire danger. Failure to comply with the fire regulations is punishable by law.

Bushfires affect weather and the atmosphere. Fires increase the amount of carbon dioxide in the air, create huge volumes of smoke and ash, and effect changes in local weather.

Maintenance of Your Home

A well maintained home has a better chance of surviving a bush fire. However, a well maintained home on its own is not enough. You need to undertake all “Five Areas for Action” to improve your chances of successfully defending your home in
a bush fire.
Maintenance activities should be conducted prior to the Bush Fire Danger Season and on a regular basis during the season to properly protect your home. The following activities are a guide only:
- Clear accumulated leaf litter and debris from around the home.
- Clean the leaves out of roof gutters.
- Trim under fences.
- Prune dead leaves and branches from bushes and plants and ensure that there are no branches overhanging your home.
Note: a permit from Council is required to remove, lop or undertake pruning of trees that are 3 metres or more in height, or are 3 metres or more in branch spread, or are 300mm or more in trunk diameter at ground level.
- Make sure that external timbers have a sound coat of paint.
- Make sure that your house number is clearly visible from the street.
- Store flammable liquids in proper containers under cover and away from the home.
- Point LPG gas tank valves away from the home.
- Check that fire fighting equipment is operational and sufficient for your needs.
- Ensure that garden hoses reach all areas of your property.
- Keep the grass mown (but not less than 50mm long) and green.
- Check that there are no gaps in roofing, windows and doors.
- Store flammable materials undercover and away from the home (e.g. wood piles, cardboard)
- Check that you have all the items you need in your household emergency kit.
- Check that your household emergency plan contains current information.
- Don’t place timber or rubbish against the back or side fences especially if the fence is between your property and a reserve or bushland.
- If you have a swimming pool, have a Static Water Supply sign placed on your front fence.
- Do not deposit tree loppings, grass clippings or other materials behind your property into Council reserves.

Preparing your home and family for bush fire

If you live close to a bush land reserve, your property has the potential to be affected by bush fire. Embers are the main cause of houses catching alight during bush fires. Burning debris such as sparks and embers are carried by wind. They can fall on or around the home, igniting small spot fires where they land. These spot fires can destroy your home if you are not prepared.

Preparing yourself, your family and your property for bush fire requires careful thought and planning. Simple steps such as cleaning leaves out of gutters and mowing long grass around your home can assist, but to improve your chances of success you need to consider the following “Five Areas for Action”:

1.Manage the vegetation around your home.
2. Design and construct new homes or modify existing homes so they are better able to withstand a bush fire.
3.Undertake regular home maintenance activities.
4.Have the appropriate fire fighting equipment.
5.Prepare your family. (hyperlinks have been removed – fact sheet is hyperlinked below)

History Of Bushfires

Bushfires are as old as trees. In Australia, trees that naturally grew in the continent were those that could best cope with the dry conditions – trees such as the fire-adapted Eucalyptus which contains plentiful oil in its leaves. Over thousands of years, the aboriginal Australian learned how to use controlled burning to drive game, clear undergrowth, and encourage renewed growth of plants. Fire for them was a tool to manage land use. Indigenous plants evolved methods to survive fires. Some of them developed reserve shoots that would sprout after a fire. Others evolved fire-resistant seeds or even seeds that were triggered on occasion of fire. Fire-encouraging species, such as the Eucalyptus, extended their area of growth while less fire-tolerant species diminished.

If A Bushfire Approaches – Leave Or Protect

Prepare as above, unless you have decided to leave early or are ordered to do so. Stay in the house after taking these precautions:
Phone 000 – don’t assume the fire service knows.
Turn off gas. Put door mats inside. Close vents, windows, doors, and block gaps from the inside with wet towels.
Fill baths, sinks, buckets and bins with reserve water.
Plug downpipes with rags and fill gutters with water.
Remove curtains, cross-tape windows and move furniture clear.
Wear long, woollen or heavy cotton clothing, solid boots or shoes, a hat or woollen balaclava, and gloves.
Hose down all walls, garden etc on sides facing the fire and watch for spot fires from flying sparks or embers.
As the main fire-front arrives, go inside with hoses, away from windows, while it passes (usually 5 to 15 minutes).
Quickly extinguish any fires which may have started in, near, or under the house or roof. Check inside roof too.
If the house is alight and can’t be extinguished, move to burnt ground. Don’t go – wait for help. Listen to battery radio for updates.

Weather And Fire

When fire danger conditions become extreme, the Bureau of Meteorology issues Fire Weather Warnings. Warnings are broadcast on radio and television. In most States and Territories, fire authorities will declare a Total Fire Ban when they receive a Fire Weather Warning from the Bureau.

Low relative humidity, high winds and lack of rain all contribute to increased fire danger. Sunshine and high temperatures rapidly dry timber and grass (fuel) which burn very quickly. Hot air can lower the moisture content of forests and grasslands to around 5 per cent and in extreme cases to 2-3 per cent, greatly increasing the speed of the fire.

Humidity: Relative humidity is the most commonly used measure of atmospheric moisture and is defined as the ratio of the amount of water vapour actually measured to that which air could hold at saturation. Very low relative humidity of, say, less than 20 per cent, causes fuels to dry out and become more flammable.

Wind: Air movement provides the oxygen the fire needs to keep burning. Higher winds mean more oxygen and more intense flames. Doubling the wind speed will quadruple the rate of spread of the fire. Winds also carry burning embers downwind, which can start new fires. This is known as spotting.

Rainfall: Dry grass, parched native shrubs and dead leaves and twigs are fire’s basic fuel. During droughts and in very hot, windy weather, even heavy fuels like large logs and the green leaves and smaller branches of large trees can become dry and flammable.

The Bushfire Threat

Large areas of Australia suffer from the threat of bushfires. The Australian climate is generally hot, dry and prone to drought. In the southeast, occasional strong winds often associated with summertime cold fronts can lead to extreme fire danger. The amount of rain in preceding months affects the amount of dry grasses. If good spring rains have resulted in abundant plant growth, late summer grass fires can be intense.

Many of Australia’s native plants burn easily. The eucalypts’ high oil content makes them particularly fire prone. The vast areas of dry grass common in mid-to-late summer also burn readily.

Most loss of life and property damage occurs around the fringes of the cities where homes are sometimes surrounded by flammable vegetation.

Varied fire seasons reflect different weather patterns. 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. Northern Australia experiences most of its fires in winter and spring.