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

Abstract

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.

Impacts of fire prevention strategies in a changing climate: an assessment for Portugal

“…FWI is the most widely used fire danger index, and several studies have relied on FWI to assess the impact of climate change on meteorological fire danger over different regions (Abatzoglou et al 2019Calheiros et al 2021, Jones et al 2022, Varela et al 2019. Some of these studies focused on Portugal (Nunes et al 2019), and others extended their scope to encompass the Iberian Peninsula (Calheiros et al 2021, Santos et al 2023 or the western Mediterranean basin (Gouveia et al 2016, Varela et al 2019. All these studies consistently point to the fact that meteorological fire danger, mainly driven by air temperature, humidity, wind speed, and precipitation, is expected to increase under climate change in western Mediterranean, due to higher temperatures (including more summer heatwaves) and less precipitation in spring and summer (Trigo et al 2016.…”

“…ERA5 has been extensively used to compute FWI in several regions of the world (Vitolo et al 2020, Carrillo et al 2022, Santos et al 2023. For instance, the EFFIS of the Copernicus emergency management service makes available a global dataset of fire danger indices based on the CFFWIS using as input reanalyzed meteorological variables from ERA5 (Vitolo et al 2020).…”

“…Recent studies provide plenty of evidence that support to a large extent this shift, namely in what concerns some of the most destructive and intense fires that have occurred in recent years in Australia, California, and the Amazon Forest (Keeley and Syphard 2019, Boer et al 2020, Libonati et al 2021. Located in a climate change hotspot (Giorgi 2006, Diffenbaugh and Giorgi 2012, Sánchez-Benítez et al 2018 at the western tip of the Mediterranean, the Iberian Peninsula, and Portugal in particular, is well-known for its summer fire occurrences, extensively studied by the scientific community (Trigo et al 2006, 2016, Garcia-Herrera et al 2010, Amraoui et al 2013, DaCamara et al 2014, Russo et al 2017, Nunes et al 2019, Turco et al 2019, Calheiros et al 2021, Bento et al 2022, Ramos et al 2023, Santos et al 2023.…”