Australian bushfire season 2019-2020 is now the climate topic of the year – severe bushfire season has caused more than 2000 houses to burn in the state of New South Wales (NSW) alone. At least 27 people has died and likely over 1 billion mammals, birds and reptiles has been lost in these fires (1).
Various media sources (1) and Wikipedia pages for 2019-2020 Bushfire season (2) provides estimates that between 8 to 11 million hectares of land has been burned so far. This really sounds severe, but how large is the amount of burned land when comparing to the earlier seasons?
Annual burned area in Australia
There are couple of excellent sources to place this bushfire season in the context. While trying to find scientific evidence into this matter I found a study Giglio at al 2013 (3). The paper describes a fourth generation Global Fire Emissions Database (GFED4). This data set was created by combining 500m MODIS burned area maps with active fire data from the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and the Along-Track Scanning Radiometer (ATSR) family of sensors. Paper also provides burned area data for Australia and New Zealand (combined) for the years 1997-2011.
But, luckily the Louis Giglio and the team has continued to work with this subject and has created excellent source of all burned area and fire-based emissions datasets you would ever need. MODIS Collection 6 (C6) MCD64A1 burned area dataset (4) provides satellite-based burned area data for all continents – and also for Australia.
All this data is available at globalfiredata.org web site with a great analysis tool available at the same place. Currently the dataset provides burned area data for the years 1997-2016. You can select continent or country and several options about the source data from emissions to burned area.
Let’s start with burned area data for Australia:
Figure: Annual burned area in millions of hectares
Figure provides the total burned area for each year between 1997 and 2016 in millions of hectares. Area burned every year was between 18.2 million hectares (2010) and 94.6 million hectares (2001). On average, the area burned during this time period was 52.9 million hectares. Since there is 769 million hectares of land in Australia, the area burned between 1997 and 2016 was 2.4 – 12.3 % of total land area – every year.
These figures seem very high and begs the question where is the land burning?
Again, the same source also provides satellite-based figures of burned area for different years. Let take year 2001 as an example.
Figure: Burned area in Australia for the year 2001
The color of each grid cell presents the percentage of area burned within this grid cell. As we can see the majority of fires are happening within the Australian northern and western territories. But in overall, the fires can happen everywhere with the exception of desert in the middle. The reason for lack of fires in the desert is of course obvious: there is nothing to burn. But if there is sufficient fuel load to burn, the fire seems to be likely at some point.
With this, placing the area burned so far during the bushfire season 2019-2020 in context is easy: The burned area as quoted by several sources is ~20% of average area burned in Australia. Thus, it is likely that the quoted area is too low, since the fires in many remote areas are not reported. The real burned area during this season will eventually be available through satellite burned area datasets.
Most of the burned land areas are acacia forests (Western territory), eucalyptus forests (North and eastern shore area), savannah and grasslands.
The above data provides the details of area being burned in total whether it is forest, non-forest and whether the fire was planned (prescriptive burns) or non-planned. But how about the forests specifically?
Forest fires in Australia
There is another source, which provides a lot of details for forest fires specifically. Australia government’s department of Agriculture provides the “Australia’s State of the Forests Report” for every five year period. The latest one has been published in 2018 (5) and covers years 2011-2016.
This report provides lots of details about forest fires in Australia starting with annual forest fires for seasons 2011-2012 to 2015-2016.
Figure: Annual planned and unplanned area of forest fires in Australia – millions of hectares
Unplanned forest fires where between 8.9 million hectares (season 2013-2014) and 21.2 million hectares (2012-2013). In addition the area burned due the planned (prescriptive) burns was between 6.2 million hectares (season 2013-2014) and 8.2 million hectares (season 2011-2012). Also we can see that this data correlates well with the satellite burned area dataset.
Earlier versions of these reports provides similar figures; for example the year 2008 version of this report says that the estimated area of forest burnt in the period from 2001 to 2006 was 24.7 million hectares; an estimated 20.0 million hectares was burnt in unplanned fires and 4.7 million hectares was burnt in planned fires. In average 15.7% of Australian forest land burned every year. According to the latest report, the total area of forest in Australia burnt one or more times during the period 2011–12 to 2015–16 was 55 million hectares (41% of Australia’s total forest area) (5). Some forests had at least one fire per year during five different years between 2011 and 2016. Thus, forest was in fire every year.
That is a lot of forest fires in one country. You would imagine that after these fires there are no forests left in Australia. But there is and according to the report, the area of forest has even increased slightly between 1990 and 2016. Most of the forested ecosystems in Australia are ecologically adapted to fire and even require it for regeneration.
For example – Eucalyptus trees do not just resist fire, they actively encourage it. Eucalyptus leaves don’t decompose and are highly flammable. Some species for these trees hold their seeds inside small capsules. Fire triggers massive drop of seeds to the ground cleaned by the forest fire (6). Due to the flammable materials generated by Eucalyptus trees, the forest fire in Eucalyptus forest is inevitable sooner or later. Sooner it happens, more controlled the fire is and less harm it will generate to the trees and animals. Avoiding fires too long is clearly not a good idea. Due to this there are a lot of planned (prescriptive burns) in Australia. Prescriptive burns are the only way of managing the volume of burnable biomass in Australian forests.
In summary, the Australian bushfire season 2019-2020 overall – despite of all the harm it has caused to lives – both for humans and animals – has not been exceptional on country level. It has not been one of the worst seasons in any metric e.g. not with the area of burned land or burned forests. But there is something special happening in New South Wales in particular.
Fires in New South Wales
Almost all the publicity regarding the 2019-2020 bushfire season in Australia has been related to the fires in New South Wales. And according to the MODIS fire count data from globalfiredata.org there is something extraordinary going in in Southeast Australia – especially in New South Wales, where the number of fires detected is about four times higher than previous records.
Figure: Eastern Australia fire counts (7)
Why the fires are so intense especially in New South Wales?
Positive Indian Ocean Dipole event
Incidentally there is an exceptional natural event going on. An exceptionally positive Indian Ocean Dipole (8) is currently ongoing (9) and has caused severe weather not only in Australia, but in Africa too (10). The event among the strongest in 60 years (12).
Why is this relevant to the extreme fires in South-East Australia? According to the study Cai et al 2009 (11) there is a systematic linkage between positive Indian Dipole events and severe fires in Southeast Australia. Almost half of most severe fires has occurred during pIOD.
Some of the studies have tried to link pIOD to the Climate Change, but so far the climate model’s ability to predict the pIOD has been less than optimal (13).
Lack of sufficient prescribed burning
According to studies, the hazardous level of fuel loads can occur within 2 to 4 years from the low intensity prescribed burning in South East Australia (14). But the prescribed burning practices are not popular among locals. “Let’s not forget, only a matter of months ago in New South Wales, we and the land management agencies, particularly national parks and forestry, we were public enemy number one because a byproduct of hazard reduction burning is smoke and yes, there’s a very significant health issue with smoke”, said NSW Rural Fire Service (RFS) Commissioner Shane Fitzsimmons for ABC News (15).
NSW has about 20 million hectares of forests, so the current level of prescribed burning (~ 200000 hectares annually) will do little to reduce the risks of catastrophic bushfires.
But one thing is sure: the debate about the right level of prescribed burning will continue (16).
- All-in-all the bushfire season in Australia is not abnormal
- Consider Australia to be a continent of fire. Most ecosystems in Australia are ecologically adapted to the fire and will even require it
- The only way to manage the fire hazards in Australia is to manage the fuel loads
- Natural Indian Ocean Dipole events (and ENSO events) has and will have the effect on droughts in Australia
- Hazardous volume of fuel loads together with abnormally positive Indian Ocean dipole and the associated drought is the reason for is the prime reason for extreme bushfire season in Southeast Australia and especially in New South Wales.
Australia’s state of forests report 1998 provides a lot of good background information about the forests and forest fires in Australia in the past.
- Giglio, L., J. T. Randerson, and G. R. van der Werf (2013), Analysis of daily, monthly, and annual burned area using thefourth-generation global fire emissions database (GFED4),J. Geophys. Res. Biogeosci.,118, 317–328, doi:10.1002/jgrg.20042.
- Giglio, L., Boschetti, L., Roy, D.P., Humber, M.L., Justice, C.O., 2018. The collection 6 MODIS burned area mapping algorithm and product. Remote Sens. Environ. 217,72–85. https://doi.org/10.1016/j.rse.2018.08.005.
- Australia’s State of the Forests Report 2018; https://www.agriculture.gov.au/abares/forestsaustralia/sofr
- 2019-2020 Australian bushfire season; image credit globalfiredata.org; image and all other images used with https://creativecommons.org/licenses/by-nc-nd/4.0/
- Cai, W., Cowan, T., & Raupach, M. (2009). Positive Indian Ocean dipole events precondition southeast Australia bushfires. Geophysical Research Letters, 36, L19710. https://doi.org/10.1029/2009GL039902
- Cai, W., and T. Cowan, 2013: Why is the amplitude of the Indian Ocean dipole overly large in CMIP3 and CMIP5 climate models? Geophys. Res. Lett., 40, 1200–1205, https://doi.org/10.1002/grl.5020
- Morrison et al 1996, Conservation conflicts over burning bush in south-eastern Australiahttps://doi.org/10.1016/0006-3207(95)00098-4