Saturday, December 3, 2022

Can prescribed burning assist in the control of wildfire? Frank Batini

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This article relates to the ongoing debate on ARR.News: Open for Debate – Bushfires, Logging, Burns & Forest Management

Frank Batini

The short answer is definitely YES. However certain conditions need to be met:

1. each prescribed burn fuel reduced buffer should be reasonably large (hundreds to thousands of hectares);

2. the individual burns need to be strategically placed giving due consideration to the prevailing “wildfire” winds; and

3. as a minimum, seven to eight per cent of the area to be protected needs to be burnt each year, so as to achieve a target of at least 40 to 50 per cent of the area with fuels that are less than 6 years old.

Prescribed burns that are small, scattered and cover less than ten per cent of the total area will inevitably fail to stop large wildfires burning under extreme conditions, such as occurred in NSW and Victoria in 2019/2020. Those who use these events to criticise the value of prescribed burning are doing the community a great disservice.

However, these disastrous wildfires have also given land managers and fire services a once-in-a-lifetime chance to get on top of the bushfire situation. By the end of this year, the fuels in the NSW and Victorian 2019/2020 fire areas will be three years old. The next few years will be a wonderful opportunity to break up these large areas of contiguous fuel by widespread prescribed burning, safely, with minimal chance of escapes. It is a chance that must not be missed.

I draw my examples from comparison of two large wildfires which burnt in the Helena catchment in 2005 and 2018.

2005

In the period 2000 to 2005, the level of prescribed burning in this water supply catchment had declined, with larger areas now carrying heavy fuel.

Then, in January 2005, on a day of low humidity and strong easterly winds, an arsonist lit a number of fires. By the time the first crews had arrived the fires were burning in the tree crowns and were throwing embers and burning bark a long way ahead. Due to the intensity at the headfire, water drops from aircraft were unsuccessful.

Another fire started by lightning eventually coalesced with the arsonist’s fires.

Fire-fighting efforts continued for about a week, hundreds of firefighters were involved and some were injured. No lives were lost and no houses burnt.

Although the fire was headed directly toward several of Perth’s suburbs, these had been protected with prescribed burns some years earlier. On reaching the fuel-reduced areas the fire behaviour changed dramatically, allowing mineral earth breaks to be constructed and the fire was contained.

This fire had burnt 27700 hectares, the cost of suppression was very high and it now posed a serious threat to the Mundaring Weir water supply.

2018

Map of 2018 fire
Map of the 2018 fire in red. Hatched and stippled areas show prescribed burns of various ages. Image: Landscope Magazine, DBCA.

In January, almost to the day and under similar weather conditions, an arsonist struck again.

Again the fires had ‘crowned” by the time crews were deployed.

However, in the 13 years between these two events additional mitigating action had been taken.

As a result of the 2005 fire and the close call with respect to water supply, the level of prescribed burning in this catchment had been increased, averaging over 10000 hectares per annum (about seven per cent of the catchment area annually). These buffers are aligned strategically to counter the prevailing summer winds (usually E, NE, NW and then SW).

The Fire Boss, aware that the headfire was heading towards the reservoir and that southern flank would be protected by a two year old prescribed burn aligned East-West, concentrated control with mineral earth breaks on the northern flank and the tailfire.

The headfire hit the waterbody and adjacent cleared shores…. and then spotted fully 150 metres onto the opposite side!

Fortunately this area had also been burnt three years previously, on a North-South alignment about four kilometres wide. The fire behaviour in the two and three year old fuels was much less intense and allowed direct attack and mineral earth breaks to be constructed.

Only 4000 hectares were burnt, again demonstrating the invaluable role that prescribed burning plays in containing wildfire under severe conditions. Suppression was safer, costs were much lower, as was the threat to water supply.

In my view the best way to tackle a wildfire is still by rapid, direct attack, construction of mineral earth breaks (with machinery or by hand) and then mop-up using water from tankers. However firefighting is now becoming increasingly reliant on water drops from fixed wing aircraft or helicopter, on backburning and with water tankers on made roads. 

Frank Batini is a forester and a consultant in Natural Resource Management. Frank is Secretary for the Bushfire Front (www.bushfirefront.org.au) a group of experienced foresters and firefighters, now retired, who advocate for sensible bushfire preparedness, mitigation and control.

Frank’s recommended reading:

David J Ward 2022 “Our dangerous friend”. Discusses burning by Aborigines, settlers and foresters. Amazon/Booktopia $25.
– Roger Underwood (Editor) 2018 Cyclone Alby. Memories of the 1978 Western Australian storm and bushfire crisis. A Bushfire Front publication.
– Frank Batini and Michael Pasotti- A tale of two fires. Landscope Magazine. Department of Biodiversity, Conservation and Attractions (DBCA)

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