And the bad news for rural and regional Australia just keeps on coming.....
‘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…
“Almost
regardless of what we do the overall extent of the fire, really, is
dictated by those climate conditions,” he said.
Climate
scientists have found climate change is exacerbating the key fire
risk factors identified by CSIRO’s study, with south-eastern
Australia becoming hotter, drier and, in a particularly worrying
trend, more prone to high wind on extremely hot and dry summer days.
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.’
[The
Sydney Morning Herald,
26
November 2021]
Nature.com,
Nature Communications,
26
November 2021, article
excerpt:
“Multi-decadal
increase of forest burned area in Australia is linked to climate
change”
Josep
G. Canadell, C. P. (Mick) Meyer, Garry D. Cook, Andrew Dowdy, Peter
R. Briggs, Jürgen Knauer, Acacia Pepler & Vanessa Haverd
Received
24 July 2020
Accepted
03 November 2021
Published
26 November 2021
Download
PDF
ABSTRACT
Fire
activity in Australia is strongly affected by high inter-annual
climate variability and extremes. Through changes in the climate,
anthropogenic climate change has the potential to alter fire
dynamics. Here we compile satellite (19 and 32 years) and
ground-based (90 years) burned area datasets, climate and weather
observations, and simulated fuel loads for Australian forests. Burned
area in Australia’s forests shows a linear positive annual trend
but an exponential increase during autumn and winter. The mean number
of years since the last fire has decreased consecutively in each of
the past four decades, while the frequency of forest megafire years
(>1 Mha burned) has markedly increased since 2000. The increase in
forest burned area is consistent with increasingly more dangerous
fire weather conditions, increased risk factors associated with
pyroconvection, including fire-generated thunderstorms, and increased
ignitions from dry lightning, all associated to varying degrees with
anthropogenic climate change.
INTRODUCTION
The
extraordinary forest fires in Australia in 2019 and 20201 have
brought further interest in detecting changes in fire activity, the
possible role of anthropogenic climate change and their likely future
trends both in Australia and globally 2,3,4,5,6.
Terrestrial
ecosystems in Australia are among the most fire prone in the world,
with fire regimes varying widely 7,8. Fire activity is
dominated by savanna and rangeland fires in the northern and western
parts of the continent characterized by fire return intervals of less
than 5 years 7,9. Forests in the east and south have fire
return times of decades to more than a century, with subtropical and
tropical forests in the northeast burning rarely or not at all 9.
Fire, including cultural burns by indigenous people, has shaped the
function and structure of most Australian ecosystems for millennia
10,11.
Against
this background of fire activity, Australia’s mean temperature has
increased by 1.4 °C since 1910 with a rapid increase in extreme
heat events, while rainfall has declined in the southern and eastern
regions of the continent, particularly during the cool half of the
year 12,13,14. These changes can affect the four
components that must simultaneously come together for fire to occur:
biomass production, its availability to burn (fuel loads), fire
weather, and ignition 7, making Australian forests
vulnerable and sensitive to changes in fire activity.
Previous
studies showed increased fire danger due to changes in weather
conditions over past decades in Australia 5,15,16, climate
change fingerprinting to individual fire events and trends 17,18,19,
and predicted increases in fire danger under future climate change
due to increasing atmospheric concentrations of greenhouse gases
2,20,21. Although these studies indicate more dangerous
weather conditions for wildfires in a warmer world, studies also
suggest that trends due to climate change might not be clearly
detectable until later in the coming decades owing to the high
natural variability and extremes of the Australian climate
4,22,23,24.
Fuel
loads and trends, as effected by climate, human activity and time
since the last disturbance, also play a role in determining fire risk
25,26. This link is a central motivation for using
prescribed burning to reduce fuel availability 27, which
in Australia is managed through changes in the frequency of
prescribed burns 28. Although there is some debate on
their value to reduce fire risk 29, particularly during
extreme fire weather conditions 2,30, fuel loads and their
distribution and structure are key determinants of fire spread,
intensity and severity 7.
Here
we analyze trends of the burned area in forest ecosystems in
Australia, which are dominated by temperate forests extending over
the southern and eastern regions of the continent. We use a
high-resolution (1.1 km x 1.1 km) burned area satellite record
available based on NOAA-AVHRR (32 years), the NASA-MODIS burned area
at 500 m resolution (19 years), and the fire histories from State
and Territory government agencies (90 years). In addition, we analyze
trends of nine wildfire risk factors and indices that relate to
characteristics of fuel loads, fire weather, extreme fire behaviour,
and ignition, which together with the burned area enable us to infer
the causal influence of climate change on fire activity.
RESULTS
Trends
in area burned
At
a continental scale, total annual burned area (fire year defined as
July to June to include the Austral summer of December to February)
using the NOAA-AVHRR dataset (“Methods”: Burned area data),
significantly increased over the past 32 years albeit with large
interannual variability (Fig. 1a; Linear fit, p value = 0.04,
Supplementary Table 1). The high variability is in part driven by
large-scale modes of atmospheric and oceanic variability such as El
Niño Southern Oscillation (ENSO) and the Southern Annual Mode 31,32
that influence fire weather conditions 16,22. Nine out of
the 11 fire years, each with more than 500,000 km2 (>50 Mha)
burned, occurred since 2000.
Forest
ecosystems also show increased burned area over time (Fig. 1b, linear
fit, p value = 0.02, Supplementary Table 1; Fig. 2). The
increasing trend is statistically significant with and without the
2019 fire year, indicating a robust increasing trend even before the
extraordinary large burned area of that year (Supplementary Table 1).
Forests in Australia experienced an annual average increase of 350%
in burned area between the first (1988-2001) and second (2002-2018)
half of the record, and an increase of 800% when including 2019. The
2019 fire year burned about three times (60,345 km2) the area of
any previous year in the 32-year AVHRR-Landgate record (Fig. 3,
Supplementary Fig. 1, “Methods”: Burned area). The burned area of
the 2019 fire year was estimated at 71,772 km2 based on State and
Territory agencies (NIAFED) and 54,852 km2 based on NASA-MODIS,
with an average for the three products of 62,323 ± 8,631. Ten
out of eleven fire years with at least 5000 km2 (>0.5 Mha)
burned have occurred since 2001. These trends are broadly consistent
across the three burned area products (Supplementary Fig. 1).
Fig.
2: Monthly burned forest area for fire years (July to June).
