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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/nhess-2020-69
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/nhess-2020-69
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  11 Mar 2020

11 Mar 2020

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This preprint was under review for the journal NHESS. A revision for further review has not been submitted.

Attribution of the Australian bushfire risk to anthropogenic climate change

Geert Jan van Oldenborgh1, Folmer Krikken1, Sophie Lewis2, Nicholas J. Leach3, Flavio Lehner4,5, Kate R. Saunders6, Michiel van Weele1, Karsten Haustein7, Sihan Li7,8, David Wallom8, Sarah Sparrow8, Julie Arrighi9,10, Roop P. Singh9, Maarten K. van Aalst9,11,12, Sjoukje Y. Philip1, Robert Vautard13, and Friederike E. L. Otto7 Geert Jan van Oldenborgh et al.
  • 1Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands
  • 2University of New South Wales, Canberra, ACT, Australia
  • 3Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK
  • 4Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 5Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, USA
  • 6Delft Institute of Applied Mathematics, Delft University of Technology, Delft, Netherlands
  • 7Environmental Change Institute, University of Oxford, Oxford, UK
  • 8Oxford e-Research Centre, University of Oxford, Oxford, UK
  • 9Red Cross Red Crescent Climate Centre, The Hague, Netherlands
  • 10Global Disaster Preparedness Center, Washington DC, USA
  • 11Faculty of Geo-information Science and Earth Observation, University of Twente, Enschede, Netherlands
  • 12International Research Institute for Climate and Society, Columbia University, New York, USA
  • 13Institut Pierre-Simon Laplace, France

Abstract. Disastrous bushfires during the last months of 2019 and January 2020 affected Australia, raising the question to what extent the risk of these fires was exacerbated by anthropogenic climate change. To answer the question for southeastern Australia, where fires were particularly severe, affecting people and ecosystems, we use a physically-based index of fire weather, the Fire Weather Index, long-term observations of heat and drought, and eleven large ensembles of state-of-the-art climate models. In agreement with previous analyses we find that heat extremes have become more likely by at least a factor two due to the long-term warming trend. However, current climate models overestimate variability and tend to underestimate the long-term trend in these extremes, so the true change in the likelihood of extreme heat could be larger. We do not find an attributable trend in either extreme annual drought or the driest month of the fire season September–February. The observations, however, show a weak drying trend in the annual mean. Finally, we find large trends in the Fire Weather Index in the ERA5 reanalysis, and a smaller but significant increase by at least 30 % in the models. The trend is mainly driven by the increase of temperature extremes and hence also likely underestimated. For the 2019/20 season more than half of the July–December drought was driven by record excursions of the Indian Ocean dipole and Southern Annular Mode. These factors are included in the analysis. The study reveals the complexity of the 2019/20 bushfire event, with some, but not all drivers showing an imprint of anthropogenic climate change.

Geert Jan van Oldenborgh et al.

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Geert Jan van Oldenborgh et al.

Geert Jan van Oldenborgh et al.

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Short summary
Southeastern Australia suffered from disastrous bushfires during the 2019/20 fire season, raising the question whether these have become more likely due to climate change. We found no attributable trend in extreme annual or monthly low precipitation, but a clear shift towards more extreme heat. However, this shift is underestimated by the models. Analysing fire weather directly, we found that the chance has increased by at least 30 %, but due to the underestimation it could be much higher.
Southeastern Australia suffered from disastrous bushfires during the 2019/20 fire season,...
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