Fire weather worsening: more heat, less rainfall

Bushfires burn on the outskirts of Canberra on Friday.

The fires during the past few months have been unique in the modern fire history of Australia because of their location, extent and rich carbon reservoirs. The latest estimates are of 10 million hectares of burnt area (and counting) in the south and southeast, making this year’s fire season the largest in the region since records began.

The fact only a small fraction of the southeast forests remain unburnt also makes this season unique. These fires are taking place after 200 years of land clearing, when the extent of temperate forests is the smallest in history. This means that as the remaining forests burn, critical habitat for many species is further reduced. At present, 49 species have had more than 80 per cent of their habitat burned, raising the question of whether some species have shifted from being threatened to endangered.

Although tens of millions of hectares burn every year, most of that is in the savannas of the Top End and in the rangelands of the centre and west where largely grasses burn. In these rangelands, the biggest fire years occur after good rains. This is in marked contrast to fires in the southeastern forests that occur during periods of drought.

Preliminary analyses from the Global Fire Emissions Database, run by a consortium of research institutions including NASA, suggests that last year fire emissions in Australia were higher than in any previous year since records began in the late 1990s. Work we are doing in conjunction with the fire emissions group for Australia’s carbon budget (calculating the net balance of all emissions and removals of greenhouse gases in Australia, which the CSIRO has been calculating since 2013) shows that fire emissions from the southeast last year were at least as high as the entire annual Australian CO2 emissions inventory from the combustion of fossil fuels, so effectively doubling the nation’s carbon footprint. The large carbon emissions this year are the result of burning some of the most carbon dense forests in the world, many accumulating hundreds of tonnes of carbon per hectare.

The CO2 emitted from forest fires can be taken up again by later regrowth over years, decades or centuries. However, the higher frequency of fires as seen in the south and southeast, and the burning of fire-sensitive ecosystems such as alpine and rain forests, leads to increasing levels of permanent degradation and permanent transfers of carbon to the atmosphere.

How did we get to this catastrophic fire season? Research done by CSIRO and the Australian Bureau of Meteorology has shown a pervasive increase in past decades of the type of weather that is highly conducive to bushfires in many parts of Australia, particularly in the south and southeast. Three components of that worsening fire weather are the observed increase in average air temperatures, the increase in frequency of extreme heat events, and the reduction of winter rainfall, which primes the forest to be drier by the time the fire season starts. With more than 30 years of national and international research, those climate trends are now unequivocally linked to the increase of greenhouse gases in the atmosphere due to the combustion of fossil fuels and multiple uses of the land here in Australia and around the world.

Those trends alone were unlikely to have led to the current catastrophic fire season, which has been spurred by a combination of factors including the current drought lasting over three years in some parts of the southeast and the culmination of 2019 being the hottest and driest year recorded in the history of this country; importantly, all these factors are driven or influenced by climate change.

Under these conditions, the magnitude and intensity of bushfires this season were no surprise. Many of the underlying trends associated with climate change that have taken us to this point will continue to increase into the future. Climate modelling done by CSIRO and the BOM shows a consistent increase in high fire danger days and worsening fire behaviour in a warmer world. For instance, CSIRO research published in 2005 showed that Canberra would have up to 24 per cent more very high or extreme fire danger days by 2020 (the catastrophic rating did not exist back then), a figure that could reach up to 66 per cent by mid-century. Our research also confirms the increased plant growth under a CO2-richer world as plants used CO2 as a building block of new growth, thus increasing the fuel loads.

It is important to highlight the role of climate extremes, which led to the extraordinary outcome last year of having the lowest rainfall since records started more than 100 years ago. Climate extremes have been part of the Australian climate for millennia, but for some of them, human-induced climate change is increasing how extreme they are becoming.

Nationally, there is an opportunity for government, disaster and resilience management agencies, research institutions and land communities to develop a resilience and adaptation plan. This will need to recognise the strong climate change link in order to understand the nature of what we want to adapt to. There is no longer a normal or even a new normal to adapt to, but rapidly changing conditions that require a longer-term adaptive management strategy.

Preliminary efforts to understand the relevance, impact and historical context of this fire season have stumbled with the fact there is no national archive of fire occurrence and associated data but many repositories in state-level agencies that hold responsibilities in fire management. There is now a great opportunity to co-ordinate an effort to bring this rich source of data into a national database to support research and the planning of resilience and adaptation strategies.

A detailed review and assessment of the current understanding of climatic, ecological and management drivers that have led to this year’s devastating fire season is also needed. This needs to include an update of research into the likely future fire activity in light of new advances in the knowledge of drivers of fire weather and the sensitivity of the climate to greenhouse gases.

There are decades of research into three main impacts of fires — the safety of people living in or near bushfire-prone areas; the impact on people of smoke inhalation; and the impacts on ecosystems. The question is how to apply and refine this knowledge in the face of a continuing trend for worsening of fire weather. Importantly, we will need mature evidence-based dialogue on a range of matters many feel strongly about.

We also need urgent efforts to protect threatened species and ecosystems, and to support the regrowth of forests. For instance, we know that salvage logging is highly detrimental to the recovery of many species, and that prescribed burning programs need to be highly tailored to the specific ecosystems and habitats intended to be protected.

Finally, we need to recognise we can never fully proof our managed landscapes and ecosystems from the likely increase in fire activity. An evidence-based approach will help us to build the resilience of local communities and make the right adaptation choices now and into the future. But only addressing the causes of human-induced climate change will stabilise the climate and prevent further impacts on our economy and natural endowment.

Pep Canadell is a chief research scientist of CSIRO Oceans and Atmosphere (and of the Earth Systems and Climate Change Hub of the National Environmental Science Program) and the executive director of the Global Carbon Project.