Guest essay by Eric Worrall

Reducing available fuel seems and obvious strategy for fire risk management. But according to the CSIRO, the real culprit is climate change.

CSIRO study proves climate change driving Australia’s 800% boom in bushfires

By Mike Foley
November 26, 2021 — 9.00pm

Climate change is the dominant factor causing the increased size of bushfires in Australia’s forests, according to a landmark study that found the average annual area burned had grown by 800 per cent in the past 32 years.

The peer-reviewed research by the national science agency, CSIRO — published in the prestigious science journal, Nature — reveals evidence showing changes in weather due to global warming were the driving force behind the boom in Australia’s bushfires.

Lead author and CSIRO chief climate research scientist Pep Canadell said the study established the correlation between the Forest Fire Danger Index – which measures weather-related vegetation dryness, air temperature, wind speed and humidity – and the rise in area of forest burned since the 1930s.

“It’s so tight, it’s so strong that clearly when we have these big fire events, they’re run by the climate and the weather,” Dr Canadell said.

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The weather system that drove a blast furnace’s worth of westerly wind across NSW and Victoria’s forests, sparking some of the worst fires of the Black Summer in 2019-20, will be up to four times more likely to occur under forecast levels of global warming.

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Last year, the bushfire royal commission reported fuel-load management through hazard reduction burning “may have no appreciable effect under extreme conditions” that typically cause loss of life and property.

The CSIRO findings bolster that conclusion and call into question calls for native forest logging to be used as a bushfire management tool.

“This is happening regardless of anything that we might or might not do to try to stop the fires,” Dr Canadell said.

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Read more: https://www.smh.com.au/politics/federal/csiro-study-proves-climate-change-driving-australia-s-800-percent-boom-in-bushfires-20211126-p59cgr.html

Do fuel reduction burns work?

There is significant evidence in Australia that the big problem with fuel reduction burns is they aren’t happening frequently enough.

From a fire services report written in 2015, Overview of Prescribed Burning in Australasia;

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Nevertheless, the lowered incidence and intensity of bushfires in areas that have been subject to extensive prescribed burning is compelling in south western WA and in the tropical savannah, but less so elsewhere.

Its effectiveness in temperate southern Australia appears to be most significant if undertaken at a rate which maintains at least 25% of land area with fuels younger than or equal to five years old. This condition is currently not achieved in any of the southern states.

There is also debate about the value of prescribed burning in improving the controllability of bushfires burning under extreme fire danger conditions, when weather appears to become the main driver of fire spread and extent. While the majority view amongst fire researchers is that low fuel levels have little effect on directly improving bushfire controllability under such conditions, reduced fuel levels can provide indirect benefits by freeing-up suppression forces and improving asset protection opportunities. Further, the mapping of burn severity after recent major bushfires has shown that low fuels from previous burning can significantly reduce the damage to a range of environmental values under extreme conditions, particularly in comparison to the damage incurred in forests with heavier fuel loads.

As the vast majority of bushfires burn under less than extreme conditions, it seems that most can be mitigated to some degree by lighter fuels derived from prescribed burning. However, predicting or empirically measuring this degree of mitigation is complex due to a range of factors including the variability of vegetation types and ages, the time since burning, the effectiveness of the burn in reducing fuel loads, and the weather conditions driving the bushfire.

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The strategy of trying to exclude fire from the hottest period of the year has reduced its incidence, but facilitated a situation whereby hot summer bushfires, when they inevitably do occur, can be far more damaging than they ever were – both in environmental and human terms.

This situation sees community pressure to take steps that sees the inevitable bushfire impacts both mitigated and minimised. A key element in any associated strategy is the managed use, in ecosystems where it is appropriate, of cool burning (or prescribed burning) to reduce the fuels available for unplanned summer bushfires.

Concurrently however, prescribed burning in southern Australia has become increasingly difficult to conduct on a significant scale due to a range of social and demographic factors and, over time, flammable fuels have continued to built-up as fuel loads have grown due to lengthy intervals between burns.

International bushfire historian and analyst Stephen Pyne (2006, Part Three, pp. 67 – 106) believes this has been exacerbated by Australian State governments, particularly since the 1970s, responding to perceived community concerns, centred largely but not exclusively in urban-based electorates, and excluding economic uses from many public lands. The redesignation, for example, of many areas of State forest as National Parks has left management agencies largely dependent on the ‘public purse’ to finance their management activities.

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Read more: https://knowledge.aidr.org.au/media/4893/overview-of-prescribed-burning-in-australasia.pdf

Australian forest want to burn. The seeds of many species of the dominant eucalyptus trees absolutely need fire to germinate, they have evolved to use fire to clear away the competition. Even when dry and dead, eucalyptus leaves and wood contains millions of microscopic pores filled with highly flammable Eucalyptus oil. Green eucalyptus leaves and small branches quite happily burn when ignited, thanks to the oil content. When Eucalyptus leaves and branches fall, which happens continuously thanks to ubiquitous wood boring insects, they naturally pile themselves into well aerated piles of kindling, ready to be ignited by the slightest spark.

I believe the apparent suggestion that fuel reduction burns don’t work is absurd. Eucalyptus forests always catch fire in the end, there is nothing we can do to prevent Australian woodlands from burning. If humans don’t burn off the accumulated fuel load, nature takes care of it for us, through lightning strikes or spontaneous combustion. All we can hope to do, through deliberate burnoffs, is control the timing and limit the damage.

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