Characteristics and controls of extremely large wildfires in the western Mediterranean Basin

Abstract

Large fires account for a disproportionally high percentage of area burned with potentially severe environmental and socioeconomic impacts. This study characterizes extremely large fires (ELFs; 2500–24,843 ha) in Portugal (1998–2013) and the concomitant fuel and weather conditions, analyzing the response of ELF size to their variation. ELF burned less shrubland‐grassland (33% of the total ELF area) than forest (59% of total), the latter primarily composed by pine and pine‐eucalypt. High fuel hazard was the norm, as indicated by median values of 0.98 for fuel load as a fraction of potential (maximum) load and time since fire >14 years over 91% of the burned area. ELF occurred under anticyclonic circulation patterns, especially ridging, and 78% of them coincided with extreme fire danger days (corresponding to infrequent conditions) in conjunction with unstable atmosphere. Containment time, fire growth rate, and energy release metrics varied by 1 more order of magnitude than ELF size, hence indicating that size alone is insufficient to describe extreme fires. Distinct combinations between ambient weather conditions, atmospheric instability, and drought defined three categories of ELF as defined by size. Quantile regression indicated that increasingly larger fires showed gradually stronger responses to fire weather severity, highlighting the difficulty in restraining fire spread in flammable landscapes in the absence of extensive fuel treatments. Data limitations inherent to the methods used are discussed, and improvements to further advance the understanding of extreme fires are suggested.

Extreme wildfire events are linked to global-change-type droughts in the northern Mediterranean

“…We acknowledge that some subjectivity was unavoidable in this exercise, but as only few ignitions turn into large fires in Mediterranean France, large fires are systematically covered and well documented. In line with the detailed description of the 2003 summer fire season performed by Favre and Schaller (2004), six large wildfire events were particularly harmful and classified as EWE for the year 2003 (Table 1). For the year 2016, three wildfires were classified as EWE.…”

“…2c). So far, this constraint avoided the occurrence of "mixed FWT fires", which combine strong winds and hot temperatures and are considered as one of the most critical FWTs in southern latitude countries (Pereira et al, 2005;Koutsias et al, 2012;Fernandes et al, 2016). But the weather conditions associated with the "Calanques" fire in the northern Mediterranean (Fig.…”

“…In a large number of ecosystems, anthropogenic ignitions are dominant and dead or live biomass is rarely limiting (Krawchuk et al, 2009;Pausas and Fernández-Muñoz, 2012). In these regions, fuel dryness therefore mainly regulates wildfires (Abatzoglou and Williams, 2016;Littell et al, 2016;Nolan et al, 2016;Fernandes et al, 2016;Turco et al, 2017). But while climate change is expected to increase the frequency and intensity of droughts in regions such as the Mediterranean (Hoerling et al, 2012), our understanding of the impact of increasing drought on EWE remains incomplete because of still-unresolved uncertainties.…”

Relevance of terpenoids on flammability of Mediterranean species: an experimental approach at a low radiant heat flux

“…Unlike other factors, vegetation can be managed to reduce the probability of occurrence of extreme wildfire (Fernandes et al 2016). Among the natural factors favouring fire, the knowledge of plant traits that enhance flammability could assist in forest management aimed at minimizing the consequences of wildfire (Ormeño et al 2009, Ganteaume et al 2013.…”

Extreme Wildfire occurrence in response to Global Change type Droughts in the Northern Mediterranean

“…For 20 instance, the association of hot, windy and dry conditions is relatively unusual in Mediterranean France because strong synoptic winds, blowing from the north, are generally associated with lower temperatures than usual (Ruffault et al, 2017) (see also Figure 2c). So far, this constraint avoided the occurrence of "mixed FWT fires", combining strong winds and hot temperatures, and that are considered as one of the most critical FWT in southern latitude countries (Pereira et al, 2005, Koutsias et al, 2012, Fernandes et al, 2016. But the weather conditions associated to the "Calanques" fire in the northern 25 Mediterranean (Figure 5c) suggest that this type of fire should be considered as an option in the near future.…”