We know that climate change is making our fire seasons longer and more intense. This brings up a range of problems and questions, including the need to increase ground and air capacity to fight fire, how we sustain volunteer and career firefighters through longer summers, how we grapple with the chance that we will get less support from overseas in coming years, and how we manage our landscapes and live in forested areas in a way that allows us to minimise the impacts of fire.
One of the tools we use to manage the intensity of fire is prescribed (or hazard or fuel reduction) burning. While Australia is a continent adapted to fire, there are ecological impacts, potentially both positive and negative, attached to fuel reduction operations.
New research says that the value of prescribed burning is declining as climate change drives more intense fire behaviour.
The report 2019–2020 Australian forest fires are a harbinger of decreased prescribed burning effectiveness under rising extreme conditions, published in Scientific Reports, looked at the effects of different rates of prescribed burning treatment on risks posed by wildfire to life, property and infrastructure.
The authors are Hamish Clarke, Brett Cirulis, Trent Penman, Owen Price, Matthias M Boer and Ross Bradstock.
In the introduction, they say:
The 2019–2020 Black Summer fires in eastern Australia raised questions about the effectiveness of prescribed burning in mitigating risk under unprecedented fire conditions. We performed a simulation experiment to test the effects of different rates of prescribed burning treatment on risks posed by wildfire to life, property and infrastructure. In four forested case study landscapes, we found that the risks posed by wildfire were substantially higher under the fire weather conditions of the 2019–2020 season, compared to the full range of long-term historic weather conditions.
For area burnt and house loss, the 2019–2020 conditions resulted in more than a doubling of residual risk across the four landscapes, regardless of treatment rate (mean increase of 230%, range 164–360%). Fire managers must prepare for a higher level of residual risk as climate change increases the likelihood of similar or even more dangerous fire seasons.
They note that there have been a range of studies into prescribed fires, with some showing a ‘significant decrease in fire severity’, with effects greater for more recent burns and weaker for older burns. Other studies found decreases in the probability of high severity fire and house loss after past fire (either prescribed fire or wildfire), but also that this effect was significantly weakened under extreme fire weather conditions.
This finding is consistent with previous research. For instance, Philip Zylstra, an adjunct associate professor at both Curtin University and the University of Wollongong and his colleagues have found that hazard-reduction burning, also known as prescribed burning, is only effective in limited circumstances and for a relatively short time.
He goes further and says that in peer-reviewed research published internationally that it is clear that large-scale burning is achieving the opposite of its intent. Rather than lessening the likelihood of future infernos, it is making forests more flammable and increasing the risk.
With more frequent intense fire coming because of climate change, we need to review the impacts of our current management practises, which are heavily focused on fuel reduction management of forests, both at the landscape level and in and around human assets like houses and towns.
Header image: Geoffrey Browne