Enhancing the fire weather index with atmospheric instability information

Abstract

The Fire Weather Index (FWI) is widely used to assess the meteorological fire danger in several ecosystems worldwide. One shortcoming of the FWI is that only surface weather conditions are considered, despite the important role often played by atmospheric instability in the development of very large wildfires. In this work, we focus on the Iberian Peninsula for the period spanning 2004–2018. We show that atmospheric instability, assessed by the Continuous Haines Index (CHI), can be used to improve estimates of the probability of exceedance of energy released by fires. To achieve this, we consider a Generalized Pareto (GP) model and we show that by stepwisely introducing the FWI and then the CHI as covariates of the GP parameters, the model is improved at each stage. A comprehensive comparison of results using the GP with the FWI as a covariate and the GP with both the FWI and CHI as covariates allowed us to then define a correction to the FWI, dependent on the CHI, that we coined enhanced FWI (FWIe). Besides ensuring a better performance of this improved FWI version, it is important to stress that the proposed FWIe incorporates efficiently the effect of atmospheric instability into an estimation of fire weather danger and can be easily incorporated into existing systems.

Global and Regional Trends and Drivers of Fire Under Climate Change

“…Dowdy and Pepler (2018) showed that there have been significant increases in the frequency of spring and summer days with 95 th percentile C-Haines index values and compound events when both fire weather and C-Haines are in their 95 th percentiles in parts of southeast Australia during 1979-2016. The compounding effect of pyroconvection on likelihood of fire have also been highlighted in the Mediterranean (Pinto et al, 2020;Tatli & Türkeş, 2014).…”

“…In our analysis, we observed strong and significant correlations between FWI and BA on both monthly and interannual timescales in the Mediterranean during 2001-2019 (Table 3; Figure 7), which is consistent with the especially strong relationships seen in prior work. Pinto et al (2020) recently highlighted the compounding impact of pyroconvective conditions on fire activity in the Mediterranean. Inclusion of the C-Haines index in predictive models of area burned by large wildfires led to improved model performance.…”

“…Pinto et al. (2020) recently highlighted the compounding impact of pyroconvective conditions on fire activity in the Mediterranean. Inclusion of the C‐Haines index in predictive models of area burned by large wildfires led to improved model performance.…”

Wildfire–atmosphere interaction index for extreme-fire behaviour

“…In cases of extreme-wildfire events, the Haines Index (Potter, 2018a) can identify dangerous fire spread conditions by using values of temperature and humidity at different elevations. Although the index was successfully used in large fire episodes in the USA (Potter, 2018b), it failed to explain or predict the behaviour of extreme fires that have happened recently (Pinto et al, 2020).…”

Wildfire-Atmosphere Interaction Index for Extreme Fire behaviour

“…In cases of extreme wildfire events, the Haines index (Potter, 2018a) can identify dangerous fire spread conditions by using values of temperature and humidity at different elevations. Although the index was successfully used in large fire episodes in the USA (Potter, 2018b), it failed to explain or predict the behaviour of extreme fires that have happened recently (Pinto et al, 2020)).…”