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‘The worst fire season ever’ … until next year

Bushfires are part of the Australian landscape and the psyche of its human inhabitants. This is particularly true as months of hot, dry weather approach. Recent warnings have predicted a dire summer ahead…

We all want to know how bad the next fire season will be, but working it out isn’t easy. AFP/Torsten Blackwood

Bushfires are part of the Australian landscape and the psyche of its human inhabitants. This is particularly true as months of hot, dry weather approach.

Recent warnings have predicted a dire summer ahead with the potential for major fires across the continent.

So will this year’s fire season be particularly bad? What are the different types of bushfire activity found across our continent? And how can these bushfire types help us predict how climate change will affect future fire seasons?

More rain = more fire

Last year, floods and high rainfall affected many regions of the continent, including large tracts of the dry interior.

A wet year, following extended dry spells, has resulted in rapid growth of grasses and herbs. This leaves a relatively dense and continuous layer of ground cover blanketing what is often bare ground.

Such conditions are the precursor to major fires, particularly as herbaceous ground cover begins to dry or “cure”. Once cured it is then available as fuel to burn.

In other years we’ve heard warnings but for different reasons. During the major droughts of recent years, warnings of a “horror” fire season were targeted at the forests that fringe our coastline, particularly in the temperate south where most Australians live.

These are our wettest environments and where plant growth or “productivity” is high. The relatively dense cover of trees, shrubs and grasses in forests provides an ever-present fuel layer of ground litter: it’s mainly the fallen leaves of trees and shrubs.

For much of the year, these litter fuels are unavailable to burn (they are too wet). But periodic, prolonged and widespread droughts dry this fuel enough that fires can readily ignite and spread.

Such circumstances – as in 2003 and 2009 – can result in fires that cause major losses of life and property on the margins of our largest cities and towns.

It’s not what starts fires, but what usually stops them

Most years, fires don’t happen because there is something stopping them. We call these things “key limitations”. When limitations break down, fire takes hold.

Where fire follows rain, as in dry ecosystems, the mass of fuel is normally too low and patchy to enable fires to spread. In wet years this limitation is overcome, as often-dormant plants start to grow.

By contrast, in our relatively moist, productive ecosystems, fuel mass and continuity is normally sufficient for fires to spread but is otherwise too wet for fires to take hold. Prolonged, extensive dry spells are needed to overcome this limitation.

In the dry country, big wet years typically occur a decade or more apart, with exceptional, extensive years – such as 2011 – occurring less frequently.

In wetter forests, major drought may occur as often as twice a decade. In cooler regions, droughts may be a decade or more apart.

AAP/Scott Webster

Up north, there are no limits

These patterns aren’t the same across the whole country. Across northern Australia’s vast, tropical savanna woodlands, conditions for fire are ideal.

The tropical grasses of these woodlands have a prolific surge of growth in response to the deluge of the wet season, providing extensive fuel every year. The ensuing six-month dry season that follows without fail, ensures this fuel is fully cured.

At the climax of the dry season, when people in Sydney and Melbourne are shivering in late winter, fire activity in the tropical north is reaching its climax under the influence of hot dry trade-winds. Up north, major fires happen annually, in contrast to other ecosystems where the right conditions occur less often.

Consequently, the average annual area burned across the top end of Australia dwarfs that which occurs elsewhere.

Our continent therefore has differing natural fire rhythms. These reflect the underlying patterns of climate and weather and the types of plants that grow in response to these conditions.

What does this mean for fire management?

From day to day, managers of land and fire need the ability to monitor the key processes that bring their local landscape into a state where it is ready to burn.

Many initiatives – such as using satellites to monitor the growth and drying of vegetation and the resultant perimeters and patterns of burning – are pivotal to this task.

Ongoing scientific research provides key insights and management tools for this purpose.

Grass fires burn far more land than fires in forested areas on the eastern seaboard. Stephen Mitchell

In the longer term, and where the primary limitation on fire is the availability of dry fuel to burn, warming and drying may mean more fires. Where the limiting factor is the lack of sufficient surface fuel, such as in many arid regions, warming and drying may mean less fire.

Given that most of the continent is dry, fire could recede across much of it in coming decades. But fire could also increase in environments where human exposure is greatest and most vulnerable (that is, the forested margins of our capital cities).

There are many complications and variants to this scenario. For one, plant growth and its rate of drying are not solely affected by these direct effects of future climate.

Fire in the future will also be influenced by a complex array of other processes, such as effects of elevated atmospheric CO₂ on plant growth, invasive drought resistant grasses, patterns of land clearing and altered rates of ignition due to changes in lightning and human populations.

These possibilities make it difficult to predict future directions. Getting a base-line understanding of how fires work in different local areas is the first step toward meeting this challenge.

Join the conversation

5 Comments sorted by

  1. Bernie Masters

    environmental consultant at FIA Technology Pty Ltd, B K Masters and Associates

    My chairing of an advisory committee that provided government with input into a draft management plan for a national park in south west WA sparked my interest in Aboriginal fire practices prior to European settlement. Thanks to the work of people like Sylvia Hallam who wrote the book Fire and Hearth in 1975, it's clear that large parts of south west WA were burnt every 2 to 4 years by Aboriginal men who lit fires in the months of January to March in moderately windy conditions but who also controlled…

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    1. David Thompson

      Science Communications at Hawkesbury Institute for the Environment (UWS) at University of Western Sydney

      In reply to Bernie Masters

      How did they contain them, do you know? With all our technology and equipment, we certainly can't control them at that time of year.

      Was it with firebreaks?

      report
  2. Eddy Schmid

    Retired

    I have been an active member of Perth Bushwalkers Club, and regularly walk the bush throughout Perth regional areas, particularly within the Hills areas and occasionly the catchment areas.
    These walks provide us with with firsthand information of what's going on with out Flora and fauna, and one thing I can say catagoricaly, the claims of excessive forrest litterand undergrowth build up this year, allegedly because of a good rainy season is FALSE !
    Totaly UNTRUE, I challenge anyone who claims the…

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  3. Shirley Birney

    retiree

    WA's on fire at present due to a controlled burn. Nasty summer ahead methinks.

    report
  4. Bernie Masters

    environmental consultant at FIA Technology Pty Ltd, B K Masters and Associates

    David, the usual way of containing a fire is: 1. firebreaks and 2: burning next to an area that has been burnt in the last few years and hence contains relatively low fuel levels. During a fire, containment lines are cut with bulldozers as firefighters do what they can at the same time as aerial water bombers drop water to protect assets or put out spot fires, etc. In some situations, lighting a fire in front of the main fire so that it will back-burn into the main fire, thereby consuming the fuel in front of where the main fire was heading, is sometimes used, but not under extreme or catastrophic weather conditions as were in force at the time that Margaret River was threatened.

    report