Wildfire Risk in a Changing Climate: Assessing spatiotemporal trends in wildfire risk in Sweden based on meteorological indices and their alignment with past fires

Sammanfattning

Forest fires are a natural disturbance in the Swedish landscape. These are largely dependent on meteorological conditions. However, anthropogenic interference and climate change are shifting natural patterns of fire behaviour. The present study examined trends in weather parameters influencing forest fire activity to improve the understanding of changing fire risk in Sweden. Data from twelve weather stations of the Swedish Meteorological and Hydrological Institute in three geographical regions (northern, central and southern Sweden) were analysed to assess spatial differences between these changes. Using the Canadian Fire Weather Index (FWI), this study identified an increase in the number of fire risk days and the duration of the fire season. Evaluating ERA 5 reanalysis data revealed an increase in maximum daily temperature and a wetting trend based on the Standardised Precipitation Evaporation Index (SPEI) across Sweden. Positive trends in fire risk were relatively stronger in the South compared to the North of Sweden. Fire risk is increasing more rapidly in spring and earlier compared to later in the summer. Burnt areas were moderately well correlated to temperature anomalies and SPEI while FWI showed nearly no predictive power. There was an overall weak correlation of parameters with fire size. However, for all large fires, a certain threshold had to be exceeded across all parameters. Overall, the results suggest an increasing wildfire risk across Sweden with especially strong trends in the South and earlier in the year. This will put additional pressure on firefighting resources making continuous research in this field crucial to protect lives and ecosystems.