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

• Published in: Natural Hazards and Earth System Sciences
• Main Authors: Krikken, Folmer Royal Netherlands Meteorological Institute , De Bilt, Utrecht . Research and Development of Weather and Climate models, Lehner, Flavio National Center for Atmospheric Research , Boulder, CO, Haustein, Karsten Univ. of Oxford . Environmental Change Inst., Drobyshev, Igor Centre for Forest Research, Montreal, Univ. of Quebec, Quebec City, QC . NSERC-UQAT-UQAM, Industrial Chair in Sustainable Forest Management; Swedish Univ. of Agricultural Sciences , Alnarp . Southern Swedish Forest Research Centre, van Oldenborgh, Geert Jan Royal Netherlands Meteorological Institute , De Bilt, Utrecht . Research and Development of Weather and Climate models
• Language: unknown
• Published: 2023
• Subjects: 54 ENVIRONMENTAL SCIENCES; Merra; Northern Sweden
• Online Access: http://www.osti.gov/servlets/purl/1849067; https://www.osti.gov/biblio/1849067; https://doi.org/10.5194/nhess-21-2169-2021

In this study, we analyse the role of climate change in the forestfires that raged through large parts of Sweden in the summer of 2018 from ameteorological perspective. This is done by studying the Canadian FireWeather 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 climatemodels (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 ~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 °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 intemperature. The other main factor, i.e. precipitation during summer months, isprojected 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) ...