Skip to main content
Research article - Peer-reviewed, 2021

Attribution of the role of climate change in the forest fires in Sweden 2018

Krikken, Folmer; Lehner, Flavio; Haustein, Karsten; Drobyshev, Igor; van Oldenborgh, Geert Jan;


In this study, we analyse the role of climate change in the forest fires that raged through large parts of Sweden in the summer of 2018 from a meteorological perspective. This is done by studying the Canadian Fire Weather Index (FWI) based on sub-daily data, both in reanalysis data sets (ERA-Interim, ERA5, the Japanese 55 year Reanalysis, JRA-55, and Modern-Era Retrospective analysis for Research and Applications version 2, MERRA-2) and three large-ensemble climate models (EC-Earth, weather@home, W@H, and Community Earth System Model, CESM) simulations. The FWI, based on reanalysis, correlates well with the observed burnt area in summer (r = 0.6 to 0.8). We find that the maximum FWI in July 2018 had return times of similar to 24 years (90% CI, confidence interval, > 10 years) for southern and northern Sweden. Furthermore, we find a negative trend of the FWI for southern Sweden over the 1979 to 2017 time period in the reanalyses, yielding a non-significant reduced probability of such an event. However, the short observational record, large uncertainty between the reanalysis products and large natural variability of the FWI give a large confidence interval around this number that easily includes no change, so we cannot draw robust conclusions from reanalysis data.The three large-ensembles with climate models point to a roughly 1.1 (0.9 to 1.4) times increased probability (non-significant) for such events in the current climate relative to preindustrial climate. For a future climate (2 degrees C warming), we find a roughly 2 (1.5 to 3) times increased probability for such events relative to the preindustrial climate. The increased fire weather risk is mainly attributed to the increase in temperature. The other main factor, i.e. precipitation during summer months, is projected to increase for northern Sweden and decrease for southern Sweden. We, however, do not find a clear change in prolonged dry periods in summer months that could explain the increased fire weather risk in the climate models.In summary, we find a (non-significant) reduced probability of such events based on reanalyses, a small (nonsignificant) increased probability due to global warming up to now and a more robust (significant) increase in the risk for such events in the future based on the climate models.

Published in

Natural Hazards and Earth System Sciences

2021, volume: 21, number: 7, pages: 2169-2179

Authors' information

Krikken, Folmer
Royal Netherlands Meteorological Institute
Lehner, Flavio
National Center Atmospheric Research (NCAR) - USA
Haustein, Karsten
University of Oxford
Université du Québec en Abitibi-Témiscamingue (UQAT)
Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre
van Oldenborgh, Geert Jan
Royal Netherlands Meteorological Institute

Sustainable Development Goals

SDG13 Climate action

UKÄ Subject classification

Climate Research
Forest Science

Publication Identifiers


URI (permanent link to this page)