Increasing concurrence of wildfire drivers tripled megafire critical danger days in Southern California between1982 and 2018

Mohammad Sadegh Khorshidi*, Philip E. Dennison, Mohammad Reza Nikoo, Amir Aghakouchak, Charles H. Luce, Mojtaba Sadegh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


Wildfire danger is often ascribed to increased temperature, decreased humidity, drier fuels, or higher wind speed. However, the concurrence of drivers-defined as climate, meteorological and biophysical factors that enable fire growth-is rarely tested for commonly used fire danger indices or climate change studies. Treating causal factors as independent additive influences can lead to inaccurate inferences about shifting hazards if the factors interact as a series of switches that collectively modulate fire growth. As evidence, we show that in Southern California very large fires and 'megafires' are more strongly associated with multiple drivers exceeding moderate thresholds concurrently, rather than direct relationships with extreme magnitudes of individual drivers or additive combinations of those drivers. Days with concurrent fire drivers exceeding thresholds have increased more rapidly over the past four decades than individual drivers, leading to a tripling of annual 'megafire critical danger days'. Assessments of changing wildfire risks should explicitly address concurrence of fire drivers to provide a more precise assessment of this hazard in the face of a changing climate.

Original languageEnglish
Article number104002
JournalEnvironmental Research Letters
Issue number10
Publication statusPublished - Oct 2020

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Science(all)
  • Public Health, Environmental and Occupational Health

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