Extreme Fire Behavior Research Articles

Patterns of fuel types and crown fire potential in Pinus halepensis forests in the Western Mediterranean Basin

Using the databases from the Spanish Forest Inventories, we have classified the forest structures of Pinus halepensis plots across the Iberian Peninsula into different fuel types as a function of the most common fire types that can be supported. The purposes of this study are to determine (i) the proportion of the different fuel types and fire type associated with different disturbance scenarios (undisturbed, after a recent wildfire, after an old wildfire and after thinning), (ii) the effect of climate and soil type on the distribution of fuel types and (iii) the effect of the different disturbance scenarios on the transitions between these fuel types. After a recent wildfire the risk of spreading active crown fires was reduced but the risk increased with time since last fire and in undisturbed areas. Climate and stoniness influenced the spatial distribution of fuel types and the potential crown fire risk. There was a lower risk of active crown fires when there was higher aridity and higher stoniness. Disturbances modify the transitions between fuel types; after a wildfire there was the highest change in fuel types with an increase of fuel type one with open forest structures and the presence of plots without trees that are linked to lower risk of active crown fires. There was also a reduction of fuel types 3 and 4, which burn with high intensity during a wildfire. In the absence of disturbances or after an old wildfire, changes between fuel types were slow, usually leading to increasing canopy closure and higher risk of active crown fires. After thinning there were also important changes in fuel types, with a reduction of active crown fire risk after thinning from below and heavy thinning. Fire plays an important role in maintaining landscape heterogeneity. As a consequence of climate warming, new areas with high structural continuity will increase the risk of extreme fire behavior, and for this reason, small wildfires and specific thinning treatments are the key to reduce crown fire potential.

Fuel types and crown fire potential in Pinus halepensis forests

There is a lack of knowledge to identify and classify forest structures according to the risk of crown fires, especially in Mediterranean regions. In this study, for the first time, we use real information, obtained after a wildfire that burnt under extreme meteorological conditions, to classify forest structures of Pinus halepensis into fuel types as a function of crown fire potential. We identified fourteen forest structures which characterize many forest types in Western Mediterranean areas depending on canopy closure, number of tree layers, percent of each tree layer and overall tree density. By using the pattern of fire types that burnt the most numerous forest structures, we have identified four fire hazard groups of forest structures which are considered different fuel types. The first two had the lowest risk of active crown fires and they differed in the proportion of surface fires and passive crown fires. The third fuel type was the threshold between structures with low and high extreme fire behavior; while the fourth had a high risk of active crown fires. Firefighters and forest managers who are demanding this kind of schema, will test and upgrade this classification of fuel types in function of crown fire potential during future wildfires.

Review of Vortices in Wildland Fire

Vortices are almost always present in the wildland fire environment and can sometimes interact with the fire in unpredictable ways, causing extreme fire behavior and safety concerns. In this paper, the current state of knowledge of the interaction of wildland fire and vortices is examined and reviewed. A basic introduction to vorticity is given, and the two common vortex forms in wildland fire are analyzed: fire whirls and horizontal roll vortices. Attention is given to mechanisms of formation and growth and how this information can be used by firefighters.

Winter desiccation and rapid changes in the live fuel moisture content of Calluna vulgaris

Background: Dramatic reductions in early-spring Calluna vulgaris moisture content have been linked to extreme fire hazard and plant die-back. Aims: To investigate spatial and temporal variation in the fuel moisture content of Calluna vulgaris. Methods: Calluna vulgaris plants were sampled in different sites and seasons to examine vertical profiles in moisture content. Live moisture content was monitored throughout autumn 2003 and spring 2004. Changes were compared to trends in temperature, soil resistance and rainfall. The effect of exposure was examined by comparing shoot moisture content in sheltered and exposed locations. Results: Significant spatial and temporal variation in moisture content was observed. In spring rapid fluctuations in moisture coincided with periods of dry weather, low temperatures and frozen ground. Shoots from exposed locations had significantly lower moisture content when the ground was frozen. Conclusions: Significant declines in the live fuel moisture content of Calluna vulgaris are associated with physiological drought caused by cold, clear conditions and frozen ground. Over-winter damage to leaf cuticles reduces the ability of the plant to regulate water loss. Changes in moisture content can be rapid, and managers should be aware of the potential for extreme fire behaviour.

Turbulent kinetic energy during wildfires in the north central and north-eastern US

The suite of operational fire-weather indices available for assessing the atmospheric potential for extreme fire behaviour typically does not include indices that account for atmospheric boundary-layer turbulence or wind gustiness that can increase the erratic behaviour of fires. As a first step in testing the feasibility of using a quantitative measure of turbulence as a stand-alone fire-weather index or as a component of a fire-weather index, simulations of the spatial and temporal patterns of turbulent kinetic energy during major recent wildfire events in the western Great Lakes and north-eastern US regions were performed. Simulation results indicate that the larger wildfires in these regions of the US were associated with episodes of significant boundary-layer ambient turbulence. Case studies of the largest recent wildfires to occur in these regions indicate that the periods of most rapid fire growth were generally coincident with occurrences of the product of the Haines Index and near-surface turbulent kinetic energy exceeding a value of 15 m2 s–2, a threshold indicative of a highly turbulent boundary layer beneath unstable and dry atmospheric layers, which is a condition that can be conducive to erratic fire behaviour.

Landscape-level habitat supply modelling to develop and evaluate management practices that maintain diverse forest values in a dry forest ecosystem in southern British Columbia

We used the TELSA forest landscape model to examine the long-term consequences of applying different forest management scenarios on indicators of wildlife habitat, understory productivity, crown fuel hazard, timber yield and treatment costs. The study area was a dry forest dominated landscape of approximately 100 000 ha near Kamloops, BC where fire safe communities, timber harvest and the maintenance of biodiversity are important social expectations. Conventional partial cut harvesting treatments maintained timber yields but strongly reduced the area supporting high snag densities, provided low levels of understory productivity and diminished the area that was undisturbed for extended periods. In contrast, the application of extensive fuel management treatments designed to prevent extreme fire behaviour diminished timber flow, but, as with partial cut harvesting, reduced the area with high snag densities and extended periods without disturbance. The application and maintenance of extensive fuel management treatments was also the most costly treatment. Alternatives, such as strategically placed fuel management treatments in critical zones around communities or areas with high investments, diminished costs and somewhat mitigated the reduction in snag densities. More complex land use zoning approaches that incorporate specific practices (e.g. protected areas) to maintain high quality wildlife habitat, and treatments that promote productive understories, appear to hold promise if multiple forest values and objectives are to be maintained in the long-term. We conclude that forest landscape modelling can and should be used to assess the consequences of current or new management initiatives prior to their application to ensure expectations regarding costs and achievement of objectives are realistic.

Wildfire and spruce beetle outbreak: Simulation of interacting disturbances in the central Rocky Mountains

Infrequent large-scale natural disturbance regimes are an integral component of Engelmann spruce (Picea engelmannii) forests of the central Rocky Mountains. Wildfires, bark beetle outbreaks, winds, and avalanches cause relatively drastic changes in community structure, composition, and function. These disturbances may occur independently or interact where the incidence of one may change the potential for another. We assessed potential wildfire behaviour change in the wake of a catastrophic, landscape-wide spruce beetle (Dendroctonus rufipennis) outbreak in southern Utah, USA. Using data collected in spruce forests affected by the outbreak, the Forest Vegetation Simulator and Fire and Fuels Extension were used to simulate long-term (100 y) stand dynamics and potential fire behaviour under 3 reconstructed scenarios: no spruce beetle outbreak (low-severity), 50% spruce beetle-caused mortality (mid-severity), and 95% spruce beetle-caused mortality (high-severity). Simulations suggested a likely reduction in probability of active crown fire for 1 or 2 decades on near-pure Engelmann spruce sites after high-severity mortality. This counterintuitive result suggested extreme fire behaviour is not an inevitable consequence of spruce beetle outbreaks. No change in potential fire behaviour was predicted in stands with the least reduction in spruce basal area (low- or mid-severity). In one stand with a history of surface fire, stand structure and potential fire behaviour from low- and high-severity simulations were influenced by surface fire ˜100 y ago. These results are indicative of complex disturbance interactions that were influenced by the host-specific spruce beetle, resultant stand structures and fuel profiles, and in one case antecedent disturbance.

Mountain Pine Beetle: From Lessons Learned to Community-based Solutions Conference Proceedings

Outbreaks of mountain pine beetle are evaluated as a generic disturbance agent, and comparisons are made with other forest disturbances such as wildfire, windthrow, and logging. A useful basis for comparison is the degree of disruption to the overstorey, understorey, and forest floor layers. Clear differences are observed in the impacts of bark beetles, fire, and windthrow, but there is overlap with various harvesting systems. Insects are selective in terms of the species or size of tree that is killed; this selectivity varies with stand composition, stand structure, and outbreak stage. The mountain pine beetle functions as part of larger natural disturbance regimes in western North America, which vary with climate and forest type. Outbreaks of many different insects occur throughout western Canada, with the relative role of fire and insects differing among ecoregions and over time. Beetle-killed stands may facilitate extreme fire behaviour and may be more susceptible to future burning. Large expanses of dead or removed trees also result in altered soil water balance and stream flows, disposing some sites to mass movement or flooding. All disturbances generate heterogeneity, with much of the value to biodiversity and ecosystem recovery depending on residual structure and biological legacies. The capacity for unassisted recovery and the value of each stand to timber supply, carbon balance, and habitat needs in a landscape context are relevant when considering salvage logging or forest rehabilitation. The future role of forest pests is expected to fluctuate in response to changes in climate and the altered composition and structure of western forests.

Can prescribed fire be used to maintain fuel treatment effectiveness over time in Black Hills ponderosa pine forests?

We determine the time frame after initial fuel treatment when prescribed fire will be likely to produce high enough mortality rates in ponderosa pine ( Pinus ponderosa var. scopulorum Dougl. ex Laws.) regeneration to be successful in maintaining treatment effectiveness in the Black Hills of South Dakota. We measured pine regeneration in disturbed stands and young pine growth rates to estimate the susceptibility of pine regeneration to prescribed fire with time since initial treatment. We also determined surface fuel accumulation rates for stands after prescribed fire to help estimate likely fire behavior in maintenance prescribed fire. Given our estimates of regeneration density and tree size, and likely fire behavior, we then used small pine tree mortality—fire effect relations to estimate the effects of prescribed fire on developing understory pine at specific times since initial treatments. Fuel treatments in ponderosa pine forests will lose their effectiveness within 10–20 years if regeneration densities are not controlled. The ability to successfully use prescribed fire to maintain low regeneration densities is dependent on seedling/sapling size and the frequency of burns. Current prescribed fire prescriptions and fuel loads are adequate to maintain low densities of ponderosa pine seedlings (<1 m tall) if burns occur every 10 years. If burn intervals exceed 15 years, regeneration can attain sizes that reduce susceptibility to prescribed fire under typical operational weather conditions. After 20–25 years, ponderosa pine can reach sizes that will require flame lengths that exceed 2 m to obtain significant mortality. Achieving these flame lengths will require burning under drier weather conditions to allow coarse woody debris (CWD) consumption to contribute to the fire intensity. Alternatively, managers can augment sites with activity fuels to increase fine fuel loadings to achieve flame lengths that will increase sapling susceptibility to fire, while burning when CWD fuel moistures are high to limit the potential for extreme fire behavior. While the flames might kill sapling-sized trees, mature overstory trees could still maintain resiliency to fire.

Climatic change and fire potential in South‐Central British Columbia, Canada

AbstractThe incidence and severity of forest fires are linked to the interaction between climate, fuel and topography. Increased warming and drying in the future is expected to have a significant impact on the risk of forest fire occurrence. An increase in fire risk is linked to the synchronous relationship between climate and fuel moisture conditions. A warmer, drier climate will lead to drier forest fuels that will in turn increase the chance of successful fire ignition and propagation. This interaction will increase the severity of fire weather, which, in turn, will increase the risk of extreme fire behaviour. A warmer climate will also extend fire season length, which will increase the likelihood of fires occurring over a greater proportion of the year. In this study of the North Okanagan area of British Columbia, Canada, the impacts of climate change of fire potential were evaluated using the Canadian Forest Fire Danger Rating System and multiple climate scenario analysis. Utilizing this approach, a 30% increase in fire season length was modelled to occur by 2070. In addition, statistically significant increases in fire severity and fire behaviour were also modelled. Fire weather severity was predicted to increase by 95% during the summer months by 2070 while fire behaviour was predicted to shift from surface fire‐intermittent crown fire regimes to a predominantly intermittent‐full crown fire regime by 2070 onwards. An increase in fire season length, fire weather severity and fire behaviour will increase the costs of fire suppression and the risk of property and resource loss while limiting human‐use within vulnerable forest landscapes. An increase in fire weather severity and fire behaviour over a greater proportion of the season will increase the risks faced by ecosystems and biodiversity to climatic change and increase the costs and difficulty of achieving sustainable forest management.

Fuels and fire behavior in chipped and unchipped plots: Implications for land management near the wildland/urban interface

Fire behavior was measured and modeled from eight 1 ha experimental plots located in the Francis Marion National Forest, South Carolina, during prescribed burns on February 12 and February 20, 2003. Four of the plots had been subjected to mechanical chipping during 2002 to remove woody understory growth and to reduce large downed woody debris from the aftermath of Hurricane Hugo in 1989. The remaining four (control) plots were left untreated. The burns were low intensity (mean flame length = 36.2 cm) and slow moving (mean spread rate = 1.18 m min −1). Neither flame length nor rate of spread differed significantly between treatments (ANOVA F's < 0.5, P > 0.7, d.f. = 1,4). Post-burn observations provided somewhat more convincing evidence of treatment effects on fire behavior. According to transect data, only slightly more than half the area in the chip plots burned as compared to upwards of 80% in the burn-only plots. BehavePlus and Hough–Albini (HA) fire models correctly predicted the low intensity, slow moving fires given the observed wind and fuel moisture conditions. Accuracy of BehavePlus predictions depended on the value for fuel height entered in the model. Use of mean fuel height for the fuel depth parameter, as is typically recommended, somewhat overestimated fire hazard in the burn-only plots. However, limiting fuel height to the observed litter depth resulted in roughly accurate predictions. HA predictions for untreated fuels were close to correct even without adjusting fuel depth. When provided with two “high-risk” fuel and fire weather scenarios both models predicted more extreme fire behavior in the untreated fuels. In contrast, chipping appeared to protect against dangerous wildfires as long as fuel heights remained low. Smoke monitoring data from a companion study carried out in the same plots indicated a 60% reduction in smoke particulate production from chipped areas, roughly consistent with predictions of the fire effects model FOFEM. Mechanical chipping is apparently a useful method for limiting fire-hazard and smoke production in long-unburned fuels. However, questions remain concerning the long-term fate of heavy chip fuels and resultant effects on fire and smoke during severe drought.

A wildfire hazard assessment and map for La Plata County, Colorado, USA

In response to the needs of local fire managers, we developed a map of wildfire hazard for La Plata County in southwestern Colorado, USA. Our measure of fire hazard had two components: (i) the probability, should fire occur under dry weather conditions, that fire behavior will be extreme, and (ii) the human values that may be lost or damaged if extreme fire behavior occurs. Using a classification approach in a GIS environment, we developed quantitative indices of potential heat release, flame length, and rate of spread for each vegetation type in the County. This is based on output of the Behave fire behavior system and adjusted for effects of slope and aspect. We then overlaid a map of residential developments to identify locations where homes are most vulnerable to wildfire damage. Results revealed a zone in the central part of the county where extensive exurban development is occurring within pine, juniper, and oak vegetation, leading to a high potential for extreme fire behavior. This assessment is notable in that (1) it treats a wide range of land ownership types including public lands, private lands, and American Indian reservations; (2) it encompasses substantial variability in vegetation/fuel types, from low-elevation semi-arid grasslands and woodlands to alpine forests and meadows to cultivated and residential lands; and (3) it maps wildfire hazard at relatively fine resolution (1 ha) for a large area (ca 4,500 km2) based on quantitative indices of wildfire behavior. Formal validation of this kind of map is nearly impossible, but we tested the final product by asking local experts to evaluate our interpretations for specific locations with which they were familiar. Feedback from the experts led us to revise some of our initial fire behavior indices, by developing custom fuel models. The same experts concluded that the final product was very accurate. By developing a relatively simple mapping algorithm, and drawing upon spatial data sources readily available to local land managers, our wildfire hazard map for La Plata County provides a template for more extensive fire hazard mapping throughout southwestern Colorado and portions of adjacent states, for use in prioritization of fire mitigation treatments and public education.

Linking Landscape Fires and Local Meteorology ─ A Short Review

Fires burning on 18th January 2003 generated a series of cumulonimbus clouds that probably exacerbated a fire that reached suburban Canberra. Powerful whirlwinds were generated, at least one of which might have been a genuine tornado. We briefly review the development of plume theory over the last fifty years and a potential atmospheric stability index that may assist in the identification of conditions that are conducive to extreme fire behaviour in the environment. This information can assist in deciding the location of future monitoring stations.

Atmospheric and fuel conditions related to the Puerto Madryn Fire of 21 January, 1994

AbstractThe atmospheric and fuel conditions that led to the case of extreme fire behaviour registered in Puerto Madryn in north‐eastern Patagonia, Argentina, on 21 January 1994 were analysed in this study. The analyses included surface and upper‐air meteorological conditions, fuel composition and load, and morphometry of the burnt area. When the fire occurred the total fuel load was 16688±2 611 kg of dry matter per hectare, with fine fuel representing 66% of the total fuel load. At the time of the major fire run, the air temperature reached 32 °C and relative humidity decreased to 13%. The fuel load and its high proportion of fine fuels, the extreme temperatures, the low relative humidity, and the changes in wind directions which resulted from the conjunction of synoptic and local‐scale phenomena, enhanced the development of a large convection column which favoured the interaction of surface and upper‐air winds. As in similar cases reported for other ecosystems, the combination of these phenomena led to this case of extreme fire behaviour. It is intended that this analysis will contribute to the future development of fire alert systems for the region and to the worldwide knowledge of extreme fire behaviour in different scenarios. Copyright © 2001 Royal Meteorological Society

A chronological overview of the 1989 fire season in Manitoba

In 1989 a new record was established for the number of fires (1147) and area burned (3.28 million ha) in Manitoba. These fires resulted in the unprecedented evacuation of 24,500 people from 32 different communities and cost over $68 million (CDN) to suppress. The first major outbreak of fires occurred in central Manitoba in mid-May and was followed by a second peak of fire activity in northern Manitoba between July 16 and August 2. Both periods were characterized by multiple fire ignitions, severe fire weather and fire danger conditions, and extreme fire behavior. A general description of the events that took place during this historic fire season are presented in this paper.