The 2019–20 wildfires in eastern Australia presented a globally important opportunity to evaluate the respective roles of climatic drivers and natural and anthropogenic disturbances in causing high-severity fires. Here, we show the overwhelming dominance of fire weather in causing complete scorch or consumption of forest canopies in natural and plantation forests in three regions across the geographic range of these fires. Sampling 32% (2.35 Mha) of the area burnt we found that >44% of the native forests suffered severe canopy damage. Past logging and wildfire disturbance in natural forests had a very low effect on severe canopy damage, reflecting the limited extent logged in the last 25 years (4.5% in eastern Victoria, 5.3% in southern New South Wales (NSW) and 7.8% in northern NSW). The most important variables determining severe canopy damage were broad spatial factors (mostly topographic) followed by fire weather. Timber plantations affected by fire were concentrated in NSW and 26% were burnt by the fires and >70% of the NSW plantations suffered severe canopy damage showing that this intensive means of wood production is extremely vulnerable to wildfire. The massive geographic scale and severity of these Australian fires is best explained by extrinsic factors: an historically anomalous drought coupled with strong, hot dry westerly winds that caused uninterrupted, and often dangerous, fire weather over the entire fire season.
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Satellite-based fire severity mapping based on Sentinel-2 satellite imagery38 was obtained for the Victorian fires from the Victorian Department of Environment, Land, Water and Planning and is available on the Victoria government spatial data portal (https://discover.data.vic.gov.au/dataset/fire-severity-map-of-the-major-fires-in-gippsland-and-north-east-victoria-in-2019-20-version-1-). Severity classes were calculated for the NSW fires using the fire extent and severity algorithm (FESM) developed by Gibson et al.39 and are available on the NSW SEED data portal (https://datasets.seed.nsw.gov.au/dataset/fire-extent-and-severity-mapping-fesm). Forest harvest date for Victoria was obtained from the Victorian Department of Environment, Land, Water and Planning and is available on the Victoria government spatial data portal (https://discover.data.vic.gov.au/dataset/logging-history-overlay-of-most-recent-harvesting-activities). Forest harvest date for NSW was obtained from NSW Forestry Corp on request, with data for older age classes within NSW supplemented with statewide land cover and trees study (SLATS) data provided by NSW Department of Planning, Industry and Environment. The 2017 NSW Landuse mapping was obtained from the NSW seed data portal (https://datasets.seed.nsw.gov.au/dataset/nsw-landuse-2017-v1p2-f0ed). Fire history and fire progression isochrons were obtained from the Victorian Department of Environment, Land, Water and Planning (https://discover.data.vic.gov.au/dataset/fire-history-overlay-of-most-recent-fires) and were provided by the NSW Rural Fire Service for NSW. Gridded FFDI data are available from the Bureau of Meteorology60. TPI was calculated from the NASA Shuttle Radar Topography Mission 90-m digital elevation model with a window of 250 m (ref. 62). Vegetation type was derived from the National Vegetation Inventory System 4.1 (https://data.gov.au/data/dataset/57c8ee5c-43e5-4e9c-9e41-fd5012536374) for Victoria and from the state vegetation formation dataset for NSW (https://www.environment.nsw.gov.au/research/Visclassification.htm).
Code for the analyses is available on FigShare at the following URL: https://figshare.com/articles/software/Drivers_of_the_Severity_and_Extent_of_2019_20_Australian_Fires_and_Forest_Management_-_Data_and_Code/14331530.
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We thank the New South Wales Government’s Department of Planning, Industry & Environment for providing funds to support this research via the NSW Bushfire Risk Management Research Hub.
The authors declare no competing interests.
Peer review information Nature Ecology & Evolution thanks the anonymous reviewers for their contribution to the peer review of this work.
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Extended Data Fig. 1 Marginal effect of topographic position index (TPI) in fire severity for the three study regions.
Marginal effect of topographic position index (TPI) in fire severity for the three study regions.
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Bowman, D.M.J.S., Williamson, G.J., Gibson, R.K. et al. The severity and extent of the Australia 2019–20 Eucalyptus forest fires are not the legacy of forest management. Nat Ecol Evol 5, 1003–1010 (2021). https://doi.org/10.1038/s41559-021-01464-6