Every year worldwide some extraordinary wildfires occur, overwhelming suppression capabilities, causing substantial damages, and often resulting in fatalities. Given their increasing frequency, there is a debate about how to address these wildfires with significant social impacts, but there is no agreement upon terminology to describe them. The concept of extreme wildfire event (EWE) has emerged to bring some coherence on this kind of events. It is increasingly used, often as a synonym of other terms related to wildfires of high intensity and size, but its definition remains elusive. The goal of this paper is to go beyond drawing on distinct disciplinary perspectives to develop a holistic view of EWE as a social-ecological phenomenon. Based on literature review and using a transdisciplinary approach, this paper proposes a definition of EWE as a process and an outcome. Considering the lack of a consistent "scale of gravity" to leverage extreme wildfire events such as in natural hazards (e.g., tornados, hurricanes and earthquakes) we present a proposal of wildfire classification with seven categories based on measurable fire spread and behavior parameters and suppression difficulty. The categories 5 to 7 are labeled as EWE.

A fuel-type map of a predominantly shrub-land area in central Portugal was generated for a fire research experimental site, by combining airborne light detection and ranging (LiDAR), and simultaneous color infrared ortho imaging. Since the vegetation canopy and the ground are too close together to be easily discerned by LiDAR pulses, standard methods of processing LiDAR data did not provide an accurate estimate of shrub height. It was demonstrated that the standard process to generate the digital ground model (DGM) sometimes contained height values for the top of the shrub canopy rather than from the ground. Improvement of the DGM was based on separating canopy from ground hits using color infrared ortho imaging to detect shrub cover, which was measured simultaneously with the LiDAR data. Potentially erroneous data in the DGM was identified using two criteria: low vegetation height and high Normalized Difference Vegetation Index (NDVI), a commonly used spectral index to identify vegetated areas. Based on the height of surrounding pixels, a second interpolation of the DGM was performed to extract those erroneously identified as ground in the standard method. The estimation of the shrub height improved significantly after this correction, and increased determination coefficients from R 2 = 0.48 to 0.65. However, the estimated shrub heights were still less than those observed in the field.Additional keywords: color infrared ortho image, fuel types, LiDAR, shrub height.

Wildfire fatalities remain a significant problem in Mediterranean Europe. Although there is a strong inter-annual variability with regard to their number, repeated tragic accidents remind us of this grim occurrence, despite the increasing firefighting capacity aimed to improve human safety. In this paper, we present an analysis of the 865 fatalities caused by wildfires in the 1945–2016 period. Data originating from national databases were merged, contextual and weather factors related to the accidents that caused these deaths were documented and analysed to explore probable relationships with the number and type of fatalities. Results show a major rise of fatalities in late 1970s in the four regions of Greece, Sardinia (Italy), Spain and Portugal. Fatalities present a strong seasonality in summer months, as expected. Overall, Spain has the highest absolute numbers of fatalities; however, normalisations by population, and burned and forest area show that annual number of fatalities is comparatively smaller. Certain other factors showed correlation with mortality. Civilians were the most affected group in Greece (65%) and Sardinia (58%), but not in Spain and Portugal. Findings indicate that an in-depth revision of fire-management policies and practices is required, with emphasis on prevention planning in urban areas, and better training of the firefighting resources.

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On 17 June 2017, one of the most dramatic and destructive wildfires in Portugal’s History started, formed by a complex of at least five wildfires that merged together burning more than 45,000 hectares. In its aftermath, 66 persons lost their lives, most of them trying to run away from the fire, more than 250 were injured, and over 1000 structures (including 263 residential homes) were damaged or destroyed, with direct losses estimated at around 200 million euros. Shortly after the fire was extinguished, and as part of a larger analysis, the authors performed exhaustive field work to assess the fire impact on all manmade structures in the area of the Pedrógão Grande fire. A specific geodatabase was built, accounting for an extensive set of parameters aimed at characterizing: (i) The structure, (ii) the surroundings of the structure, and (iii) the arrival and impact of the fire. A total of 1043 structures were considered for the analysis, mostly support structures, like sheds or storage (38.6%), but also around 25% of dwellings (13.3% primary and 11.9% secondary). Regarding the ignitions, more than 60% of the structures were ignited due to the deposition of firebrands in different weak points. In addition, more than 60% of these ignitions occurred on the roofs, mainly because of the vulnerability associated with the structures and materials supporting them. Despite these results, and from what we observed on the structures that were not destroyed, we still consider that for the Portuguese reality houses are a good refuge, providing that they and their surroundings are managed and kept in good conditions.

The influence of a mesoscale convective system (MCS) in the evolution of two wildfires that started during the afternoon of 17 June 2017 in Pedrógão Grande, Central Portugal is discussed and analysed using weather radar data, weather stations, video images and fire spread analysis. As the MCS approached the region, its convectively driven flows started to influence the fires. The overturning flows were formed by two main limbs: one organised as front-to-rear deep layer inflows that propagated over the convective region of the MCS and the other as rear-to-front mid-level inflows that descended below the anvil structure of the MCS. The rear-to-front inflows, while accelerating and descending to lower levels, contributed to modify the fires’ intensity and plume characteristics. After the two fires merged, the resulting junction fire became very intense and impossible to control. Then, a firestorm was generated, causing the deaths of 66 people. The main goal of this study is to detail the influence of the MCS in the fire spread, thus contributing to the general knowledge of outstanding fire behaviour modifications due to the influence of atmospheric convective processes.

The biggest fire fighting accident in the history of Croatia happened on August 30, 2007. The routine fire fighting operation ended with 12 dead and 1 badly injured fire-fighter. That was the biggest human loss in the history of fire fighting in Croatia. In order to understand the Kornati accident a research team was formed and independent scientific investigation performed. The accident was analyzed from meteorological, vegetation, thermodynamics and aerodynamic points of view, and several simulation models of fire propagation were used. This paper describes in detail one possible explanation connected with eruptive fire behavior. Eruptive fire behavior has been reported in many fire accidents in the past causing a lot of causalities. Based on the real Kornati accident data, the eruptive fire model was conceived and appropriate results derived. The paper describes them in detail. Our aim in studying this and other accidents is not to find who is guilty or to blame anyone but rather to find what happened and to extract lessons, to avoid future accidents.

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