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.

The summer of 2003 was characterised by exceptional warm weather in Europe, particularly during the first two weeks of August, when a devastating sequence of large fires was observed, reaching an amount of circa 450 000 ha, the largest figure ever recorded in Portugal in modern times. They were concentrated in two relatively confined regions of Portugal and a considerable proportion of burnt area was due to fires started on the 2nd and 3rd of August. It is shown that the 850 hPa temperature values observed over Portugal for the 1st and 2nd of August 2003 were the highest recorded since 1958. Using data from synoptic stations covering the entire Portuguese territory, the event was characterised in fine detail, including the evolution of both maximum and minimum temperatures, surface relative humidity, and wind anomaly fields. The different spatial extent of maximum and minimum temperatures is analysed leading to the new all-time Portuguese records of 47.3 °C for maximum and 30.6 °C for minimum temperatures that were recorded on the 1st of August near the main area of occurrence of the largest fire. Finally, it is shown that the summer of 2003 was preceded by a wet winter followed by a very dry month of May, a precipitation anomalous regime that contributed to a climatic background that favoured the role played by the early August heatwave and the associated meteorological surface conditions. Copyright © 2006 Royal Meteorological Society

When tree‐species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light‐related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density. In this study, measurements of tree sizes and stand structures were combined with a detailed tree‐level light model (Maestra) to examine the contribution of each light‐related interaction on tree‐ and stand‐level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures ofFagus sylvaticaandPinus sylvestris(63 plots). These sites were distributed across the current distribution of these species within Europe. Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light‐related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. sylvatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length. The mixing effects on light absorption were only correlated with the mixing effects on growth forP. sylvestris, suggesting that the mixing effects on this species were driven by the light‐related interactions, whereas mixing effects onF. sylvaticaor whole community growth were probably driven by non‐light‐related interactions. Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light‐related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop.

We focus here on a mainland Continental Portuguese Rural Fire Database (PRFD) that includes 450 000 fires, the largest such database in Europe in terms of total number of recorded fires in the 1980–2005 period. In this work, we (a) list the most important factors for triggering and controlling the fire regime in mainland Continental Portugal, (b) describe the dataset's production, (c) discuss procedures adopted to identify and correct different fire data inconsistencies, creating a modified PRFD which we use here and make available as Supplement, (d) explore some basic temporal and completeness properties of the data. We find that the dataset's minimum measured burnt areas have changed with time between A_F = 0.1 ha (1980–1990), A_F = 0.01 ha (1991–1992), and A_F = 0.001 ha (1992–2005), with varying degrees of completeness down to these values. These changes in minimum area measured are responsible for greater numbers of fires being recorded. A relatively small number of large fires in the PRFD are responsible for the majority of the burnt area. For example, fires with A_F > 100 ha represent about 1% of all fire records but 75% of total burnt area. Finally, we consider for each Continental Portugal district and for the 26-yr period, the total number of rural fires and area burnt in forests and shrublands, each normalized by district areas. We find that the highest numbers of fires per unit area are in highly populated districts, and that the largest fraction of burnt area is in forested areas, coinciding with large parcels of continuous forests (predominantly rural and moderately urban areas).