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Observed increases in extreme fire weather driven by atmospheric humidity and temperature

Abstract

Recent increases in regional wildfire activity have been linked to climate change. Here, we analyse trends in observed global extreme fire weather and their meteorological drivers from 1979 to 2020 using the ERA5 reanalysis. Trends in annual extreme (95th percentile) values of the fire weather index (FWI95), initial spread index (ISI95) and vapour pressure deficit (VPD95) varied regionally, with global increases in mean values of 14, 12 and 12%, respectively. Significant increases occurred over a quarter to almost half of the global burnable land mass. Decreasing relative humidity was a driver of over three-quarters of significant increases in FWI95 and ISI95, while increasing temperature was a driver for 40% of significant trends. Trends in VPD95 were predominantly associated with increasing temperature. These trends are likely to continue, as climate change projections suggest global decreases in relative humidity and increases in temperature that may increase future fire risk where fuels remain abundant.

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Fig. 1: Significant trends in extreme fire weather.
Fig. 2: Anomalies in annual extreme fire weather metrics.
Fig. 3: Global attribution of FWI95 trends.
Fig. 4: Attribution of FWI95 trends by region.
Fig. 5: Trends in T and Td and relationship with extreme fire weather trends.

Data availability

The hourly ERA5 data used for this study are available at https://doi.org/10.24381/cds.adbb2d47. The fire weather metrics derived for the period 1979–2020 that support the findings of this study are available from https://doi.org/10.5281/zenodo.5567021 (daily ISI and FWI) and https://doi.org/10.5281/zenodo.5567062 (daily maximum VPD). Global mean land-surface temperatures are available from the NOAA National Centers for Environmental information, Climate at a Glance: Global Time Series (published July 2021), at https://www.ncdc.noaa.gov/cag/. The global biomes used in this study are available at https://www.worldwildlife.org/publications/terrestrial-ecoregions-of-the-world and land-cover data are available at https://doi.org/10.5067/MODIS/MCD12Q1.006.

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Acknowledgements

We thank the Canadian Partnership for Wildland Fire Science for their support. P.J. thanks M. McElhinny and J. Beckers for their help in developing code for FWI calculation. J.T.A. was partially supported by NSF award no. OAI-2019762.

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P.J. and M.D.F. designed the initial study. All authors contributed to discussions regarding further development of the study design and analysis. D.C-A., P.J. and J.T.A. performed the analysis. S.C.P.C. and P.J. wrote the manuscript. All authors contributed to review and revision of the manuscript.

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Correspondence to Piyush Jain.

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Peer review information Nature Climate Change thanks Ubirajara Oliveira and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Jain, P., Castellanos-Acuna, D., Coogan, S.C.P. et al. Observed increases in extreme fire weather driven by atmospheric humidity and temperature. Nat. Clim. Chang. 12, 63–70 (2022). https://doi.org/10.1038/s41558-021-01224-1

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