Fire, Volume 4, Issue 2 (June 2021) – 16 articles

Fuel beds represent the layer of fuel that typically supports continuous combustion and wildland fire spread. We examine how wind propagates through and above loose and packed pine needle beds and artificial 3D-printed fuel beds in a wind tunnel. Vertical profiles of horizontal velocities are measured for three artificial fuel beds with prescribed porosities and two types of fuel beds made with long-leaf pine needles. The dependence of the mean velocity within the fuel bed with respect to the ambient velocity is linked to the porosity. Experimental results show significant structure to the vertical profile of mean flow within the bed, and suggest that small-scale sweeps and ejections play a role in this system redistributing momentum similar to larger-scale canopy flows. Full article

Mountain forests are subjected to several pressures including historical land-use changes and climate warming which may lead to shifts in wildfire severity negatively impacting tree species with low post-fire growth resilience. This is the case of relict Mediterranean Scots pine (Pinus sylvestris) forests in the Sierra de Gredos mountains (central Spain). We reconstructed the historical fire regime of these forests since 1700 by using paleoecology, historical ecology and dendroecology. We detected an increase in charcoal accumulation rate and coprophilous fungi in peat bogs during the late 19th century when the pine pollen percentage sharply decreased, historical records of fire peaked and many trees showed growth suppressions. We inferred an increased wildfire incidence during the late 19th century, which could have shaped the current distribution of Scots pine forests. This shift in fire-forest interactions can be explained by the uncontrolled use of mountain forests and grasslands due to the dissolution of “Mesta”, one of the major and lasting transhumance livestock associations in Europe. Integrating historical human and climate influences on fire regimes allows decomposing the resilience and conservation components of relict forests. Full article

The unprecedented size of the 2017 wildfires that burned nearly 600,000 hectares of central Chile highlight a need to better understand the climatic conditions under which large fires develop. Here we evaluate synoptic atmospheric conditions at the surface and free troposphere associated with anomalously high (active) versus low (inactive) months of area burned in south-central Chile (ca. 32–41° S) from the Chilean Forest Service (CONAF) record of area burned from 1984–2018. Active fire months are correlated with warm surface temperatures, dry conditions, and the presence of a circumpolar assemblage of high-pressure systems located ca. 40°–60° S. Additionally, warm surface temperatures associated with active fire months are linked to reduced strength of cool, onshore westerly winds and an increase in warm, downslope Andean Cordillera easterly winds. Episodic warm downslope winds and easterly wind anomalies superimposed on long-term warming and drying trends will continue to create conditions that promote large fires in south-central Chile. Identifying the mechanisms responsible for easterly wind anomalies and determining whether this trend is strengthening due to synoptic-scale climatic changes such as the poleward shift in Southern Hemisphere westerly winds will be critical for anticipating future large fire activity in south-central Chile. Full article

This work provides a detailed overview of existing investigations into the fire–wind interaction phenomena. Specifically, it considers: the fanning effect of wind, wind direction and slope angle, and the impact of wind on fire modelling, and the relevant analysis (numerical and experimental) techniques are evaluated. Recently, the impact of fire on buildings has been widely analysed. Most studies paid attention to fire damage evaluation of structures as well as structure fire safety engineering, while the disturbance interactions that influence structures have been neglected in prior studies and must be analysed in greater detail. In this review article, evidence regarding the fire–wind interaction is discussed. The effect of a fire transitioning from a wildfire to a wildland–urban interface (WUI) is also investigated, with a focus on the impact of the resulting fire–wind phenomenon on high- and low-rise buildings. Full article

Development of comprehensive spatially explicit fire occurrence data remains one of the most critical needs for fire managers globally, and especially for conservation across the southeastern United States. Not only are many endangered species and ecosystems in that region reliant on frequent fire, but fire risk analysis, prescribed fire planning, and fire behavior modeling are sensitive to fire history due to the long growing season and high vegetation productivity. Spatial data that map burned areas over time provide critical information for evaluating management successes. However, existing fire data have undocumented shortcomings that limit their use when detailing the effectiveness of fire management at state and regional scales. Here, we assessed information in existing fire datasets for Florida and the Landsat Burned Area products based on input from the fire management community. We considered the potential of different datasets to track the spatial extents of fires and derive fire history metrics (e.g., time since last burn, fire frequency, and seasonality). We found that burned areas generated by applying a 90% threshold to the Landsat burn probability product matched patterns recorded and observed by fire managers at three pilot areas. We then created fire history metrics for the entire state from the modified Landsat Burned Area product. Finally, to show their potential application for conservation management, we compared fire history metrics across ownerships for natural pinelands, where prescribed fire is frequently applied. Implications of this effort include increased awareness around conservation and fire management planning efforts and an extension of derivative products regionally or globally. Full article

Large forest fires have repeatedly affected Europe, in particular the Mediterranean countries. It is now crucial to continue the effort to feed the several layers of prediction models and understand how wildfire spreads in order to develop modern preventative and mitigation methods. The present study evaluates the performance of Sentinel 5-P TROPOMI for the monitoring of carbon monoxide (CO) and methane (CH₄) during extreme fire events in Portugal, focusing on the Monchique (2018) and Vila de Rei/Mação (2019) wildfires, which devastated 27,154 ha and 9249 ha, respectively. The spatial distribution and trend of CO and CH₄ prior to, during, and following the fire event were accessed and linked with in situ data in a qualitative and quantitative exploration. Large CO plumes were observed with CO columns exceeding 4.5 × 10¹⁸ and 6 × 10¹⁸ molecules/cm² on 21 July 2019, and 7 August 2018, respectively. CO distribution profiles after consecutive digital processing steps showed the ability to follow CO fluctuations according to the fire spread. Furthermore, statistically significant differences were found between CO emissions inside and outside the burning area in both fire events. Finally, the CO₂ estimated through CO column data presented an emission of 7.6 × 10¹⁹ molecules/cm² for the uppermost emission day on 7 August 2018. Although CH₄ monitoring is still unwavering to draw exact conclusions, the CO patterns during extreme fire events show promising and consistent data when compared with in situ data. Full article

While western U.S. wildfires have increased in intensity and scale, their impacts on soil chemical composition and hydraulic processes have received little attention, despite increasing erosion, surface runoff and flooding. The relationships between biomass-burning emissions, composition of the soil, fire heat, and soil water repellency are fragmental and sometimes contradictory. Here, we characterized the water repellency of sand (soil surrogate) exposed to Jeffrey pine duff smoke under controlled laboratory conditions. Water drop penetration time (WDPT), effective contact angle, and relative sorptivity of exposed silica sand (soil surrogate) were determined. Sand samples treated with smoke and heat or with cold smoke showed severe-to-extreme water repellency (WDPT > 1020 s). Sand samples exposed to fulvic acid (surrogate for soil organic matter) showed strong water repellency (WDPT = 81 s) that increased to become severe (WDPT = 2305 s) after subsequent heating to 200 °C for two hours. All sand samples exposed to either fire emissions or fulvic acid showed WDPTs >81 s, effective contact angles between 78° and 87°, and relative sorptivities between 0.31 and 0.49 compared with the untreated sand samples, with a WDPT <0.5 s, effective contact angle of 48°, and relative sorptivity of 1. This indicates that the sorptivity-controlled water infiltration into treated sand is less than half of that into untreated sand. Full article

Imperata cylindrica is a perennial grass that often proliferates in fire-affected forests. Recent fire events have been consistently associated with a lowering of soil nitrogen (N) to phosphorus (P) ratios. Thus, I. cylindrica might have a tendency toward P-limited growth and/or tolerance for low soil N availability that confers a competitive advantage post-fire. We contrasted soil and I. cylindrica chemistry between recently burned and unburned areas in eastern Australia. Imperata cylindrica foliar N:P ratios were 21% lower in burned areas than in unburned areas, reflecting an increase in the uptake of P, but not N, post-fire, consistent with P-limitation. We then grew I. cylindrica seedlings in soils with differing fire-exposure histories and subjected them to various resource amendments (including N and P addition). Survival of I. cylindrica seedlings was not affected by the fire-exposure history of soil, but was reduced by 66% through N-addition. Soil fire history did not significantly affect I. cylindrica growth, but addition of P greatly enhanced I. cylindrica growth, particularly on unburned soils. Our results indicate that the association between I. cylindrica and forest fire regime could be facilitated, in part, by the short-term positive effect of fire on soil phosphorus and the long-term positive effect of fire-exclusion on soil nitrogen, particularly on well-weathered soils. Full article

Fire risk can be defined as the probability that a fire will spread across a landscape, that therefore determines the likely area burnt by a wildfire. Reliable monitoring of fire risk is essential for effective landscape management. Compilation of fire risk records enable identification of seasonal and inter-annual patterns and provide a baseline to evaluate the trajectories in response to climate change. Typically, fire risk is estimated from meteorological data. In regions with sparse meteorological station coverage environmental proxies provide important additional data source for estimating past and current fire risk. Here, we use a 60-year record of daily flows (ML day⁻¹ past a fixed-point river gauge) from two rivers (Franklin and Davey) in the remote Tasmanian Wilderness World Heritage Area (TWWHA) to characterize seasonal patterns in fire risk in temperate Eucalyptus forests and rainforests. We show that river flows are strongly related to landscape soil moisture estimates derived from down-scaled re-analysis of meteorological data available since 1990. To identify river flow thresholds where forests are likely to burn, we relate river flows to known forest fires that have occurred in the previously defined ecohydrological domains that surround the Franklin and Davey catchments. Our analysis shows that the fire season in the TWWHA is centered on February (70% of all years below the median river flow threshold), with shoulders on December-January and March. Since 1954, forest fire can occur in at least one month for all but four summers in the ecohydrological domain that includes the Franklin catchment, and since 1964 fire could occur in at least one month in every summer in the ecohydrological domain that includes the Davey catchment. Our analysis shows that managers can use river flows as a simple index that indicates landscape-scale forest fire risk in the TWWHA. Full article

As the possibility of safe escape is one of the most crucial aspects of a building’s fire safety features, understanding of human behaviour under fire conditions is important for a successful evacuation. Although most of today’s buildings are equipped with fire safety systems, a fire can still occur at anytime and anywhere in a building and have devastating consequences. In the last decade, researchers and practitioners have used information technology to assist with fire safety design and emergency management. Building Information Modelling (BIM) is an exemplar process whose underpinning digital technology has been helpful for fire safety design, simulation, and analysis, but there is a lack of research on how BIM-based models combined with agent-based simulations can help improve evacuation via effective navigation and wayfinding in high-rise residential buildings. Customising evacuation instructions based on BIM, simulation results and occupant location, and delivery of these bespoke instructions to occupants’ smartphones during a fire emergency is relatively novel and research is needed to realise the potential of this approach. Therefore, this study investigates how customised evacuation instructions delivered to each occupant in a high-rise residential building could result in a faster evacuation during a fire incident. The research adopted a case study building and used Pathfinder (agent-based evacuation simulation software) to simulate evacuation from this eleven-floor high-rise residential building in Cairo, Egypt. Constraining evacuees (simulated agents in Pathfinder) to take particular exit routes was used as a proxy for delivering customised evacuation instructions to actual evacuees. Simulation results show that, in general, allowing the use of lifts for the benefit of disabled occupants could lead to their misuse by able-bodied occupants; evacuees would attempt to use the first visible point of exit regardless of how crowded it is. With optimally customised instructions, the evacuation time was, on average, 17.6 min (almost 50%) shorter than when the occupant’s choice of egress route was simulated based on standard path planning factors such as route length, nearby crowds and visible hazards. With evacuation instructions sent via smartphones, occupants could exit more rapidly via alternative routes. Such bespoke instructions were shown to reduce the adverse effects of crowdedness and uneven distribution of occupants along vertical and horizontal evacuation routes on evacuation time. Full article

Rapid estimates of the risk from potential wildfires are necessary for operational management and mitigation efforts. Computational models can provide risk metrics, but are typically deterministic and may neglect uncertainties inherent in factors driving the fire. Modeling these uncertainties can more accurately predict risks associated with a particular wildfire, but requires a large number of simulations with a corresponding increase in required computational time. Surrogate models provide a means to rapidly estimate the outcome of a particular model based on implicit uncertainties within the model and are very computationally efficient. In this paper, we detail the development of a surrogate model for the growth of a wildfire based on initial meteorological conditions: temperature, relative humidity, and wind speed. Multiple simulated fires under different conditions are used to develop the surrogate model based on the relationship between the area burnt by the fire and each meteorological variable. The results from nine bio-regions in Tasmania show that the surrogate model can closely represent the change in the size of a wildfire over time. The model could be used for a rapid initial estimate of likely fire risk for operational wildfire management. Full article

We investigate the spatiotemporal patterns of prescribed fire and wildfire within Washington State, USA using records from the state’s Department of Natural Resources (DNR). Spatiotemporal comparisons of prescribed fire and wildfire area burned revealed that (1) fire activity broadly differed between the eastern and western portion of the state in terms of total area and distribution of burn sources, (2) over the 2004–2019 period, wildfire largely replaced prescribed fire as the predominant source of burning, and (3) wildfire and prescribed fire occur during distinct months of the year. Spatiotemporal variation in prescribed fire activity at regional levels were measured using five parameters: total area burned, total biomass burned, burn days, burn approval rates, and pile burn frequency. Within-region spatial variability in prescribed fire parameters across land ownership categories and bioclimatic categories were often detectable. Regression models of the annualized prescribed fire parameters suggested that prescribed fire activities have been declining in multiple administrative regions over the 2004–2019 period. A descriptive analysis of seasonal trends found that prescribed fire use largely peaked in the fall months, with minor peaks usually occurring in the spring. Lastly, we described how area burned, biomass burned, and pile burn frequency differed between prescribed fires approved and denied by the DNR, and found that approved prescribed fires were typically smaller and burned less biomass than denied fires. Full article

Adapting to the growing frequency of catastrophic wildfires in Greece and mitigating their effects is a complex socio-ecological problem. We used an online survey to query more than 100 engaged stakeholders who can potentially influence possible legislation and fire management organizational reform, emphasizing civil protection agencies and research entities. We focused the questionnaire on the importance of different wildfire effects to understand which were considered negative or unacceptable, indifferent, or positive. For fire prevention, we examined the range of acceptance and views on fuel management and fire use activities that are limited in extent or not allowed in Greece. We also examined the beliefs regarding ignition causes and responsibility, in addition to how different policies might reduce wildfire-related problems. The results revealed an emphasis on reforming wildfire management policies to deal with the way society and agencies function and interact, and mitigate the influence of climate change in wildfire frequency and behavior. In addition, respondents had a negative stance towards allowing wildfires to burn for resource objectives and a strong belief that arsonists are behind most ignitions. They also believe the lack of a national cadaster system is a major source of wildfire-related problems. The results indicate little support for fuel treatments, but increased acceptance for the legalization of fire use during firefighting (backfires). This study summarizes current wildfire perceptions in Greece and identifies opportunities and barriers to changes in wildfire governance to improve risk management programs and guide post-fire management and mitigation. Full article

Indigenous land use and climate have shaped fire regimes in southeast Australia during the Holocene, although their relative influence remains unclear. The archaeologically attested mid-Holocene decline in land-use intensity on the Furneaux Group islands (FGI) relative to mainland Tasmanian and SE Australia presents a natural experiment to identify the roles of climate and anthropogenic land use. We reconstruct two key facets of regional fire regimes, biomass (vegetation) burned (BB) and recurrence rate of fire episodes (RRFE), by using total charcoal influx and charcoal peaks in palaeoecological records, respectively. Our results suggest climate-driven biomass accumulation and dryness-controlled BB across southeast Australia during the Holocene. Insights from the FGI suggest people elevated the recurrence rate of fire episodes through frequent cultural burning during the early Holocene and reduction in recurrent Indigenous cultural burning during the mid–late Holocene led to increases in BB. These results provide long-term evidence of the effectiveness of Indigenous cultural burning in reducing biomass burned and may be effective in stabilizing fire regimes in flammable landscapes in the future. Full article

Wildfire size and frequency have increased in the western United States since the 1950s, but it is unclear how seeding treatments have altered fire regimes in arid steppe systems. We analyzed how the number of fires since 1955 and the fire return interval and frequency between 1995 and 2015 responded to seeding treatments, anthropogenic features, and abiotic landscape variables in Wyoming big sagebrush ecosystems. Arid sites had more fires than mesic sites and fire return intervals were shortest on locations first treated between 1975 and 2000. Sites drill seeded before the most recent fire had fewer, less frequent fires with longer fire return intervals (15–20 years) than aerially seeded sites (intervals of 5–8 years). The response of fire regime variables at unseeded sites fell between those of aerial and drill seeding. Increased moisture availability resulted in decreased fire frequency between 1994 and 2014 and the total number of fires since 1955 on sites with unseeded and aerially pre-fire seeding, but fire regimes did not change when drill seeded. Greater annual grass biomass likely contributed to frequent fires in the arid region. In Wyoming big sagebrush steppe, drill seeding treatments reduced wildfire risk relative to aerial seeded or unseeded sites. Full article

Non-stand-replacing wildfires are the most common natural disturbance in the tall eucalypt forests of Tasmania, yet little is known about the conditions under which these fires burn and the effects they have on the forest. A dry lightning storm in January 2019 initiated the Riveaux Road fire. This fire burnt nearly 64,000 ha of land, including tall eucalypt forests at the Warra Supersite. At the Supersite, the passage of the fire was recorded by a suite of instruments measuring weather conditions and fluxes (carbon, water and energy), while a network of permanent plots measured vegetation change. Weather conditions in the lead-up and during the passage of the fire through the Supersite were mild—a moderate forest fire danger index. The passage of the fire through the Supersite caused a short peak in air temperature coinciding with a sharp rise in CO₂ emissions. Fine fuels and ground vegetation were consumed but the low intensity fire only scorched the understorey trees, which subsequently died and left the Eucalyptus obliqua canopy largely intact. In the aftermath of the fire, there was prolific seedling regeneration, a sustained reduction in leaf area index, and the forest switched from being a carbon sink before the fire to becoming a carbon source during the first post-fire growing season. Full article