An Evaluation of the Atmospheric Instability Effect on Wildfire Danger Using ERA5 over the Iberian Peninsula

The Fire Weather Index (FWI) is used to assess meteorological fire danger worldwide. It has been argued that it lacks an atmospheric instability term. A new enhanced FWI (FWIe) was recently developed incorporating atmospheric instability in the form of the Continuous Haines Index (CHI). Here, the first climatological and evolution analysis of these indexes was performed using ERA5 data for the 1980-2020 period. There was a prevalence of higher values over central Iberia; these were heavily modulated by the climate types, topography, and land cover. Southwest and east Iberia suffered the greatest decadal increases in all three indexes. Relating both indexes to occurrences detected by satellite, through fire radiative power (FRP), showed that FWIe provided an improved meteorological fire danger assessment in higher-risk conditions. This showed that greater-risk observations were more prone to be affected by atmospheric instability than lower-danger observations. Case studies for the 2017 central Portugal and 2003 and 2018 Monchique wildfires were additionally conducted to verify these conclusions. This work points to the usefulness of FWIe when/where atmospheric instability may play a critical role in the development of wildfires, which may contribute to a more focused deployment of suppression mechanisms by the authorities.

Automated summary

The Fire Weather Index (FWI) is widely used for fire danger assessment, but lacks an atmospheric instability term. The enhanced FWI (FWIe) incorporating atmospheric instability in the form of CHI was developed. Climatological and evolution analysis using ERA5 data showed higher FWI values over central Iberia influenced by climate types, topography, and land cover. FWIe improved the assessment of meteorological fire danger in higher-risk conditions and was more affected by atmospheric instability. Case studies verified the usefulness of FWIe in wildfire development and suggested a focused deployment of suppression mechanisms.