Fire Behavior

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Fire severity change with disturbance into fuel treatments

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Researchers measured 14 transects across two different fuel treatment types on three different units. For both fuel treatment types, only ladder fuels had been removed. They found that while severity was reduced at all sites, the spatial distribution of fire severity within the treatment areas varied by treatment type and unit as well as which fire severity metric they were analyzing. They found fuel treatments reduced fire severity anywhere from -7 m to 533 m into the treatment area. Kennedy and Johnson (2014) caution that local site conditions, topography and vegetation type will be other sources of variation in fire severity.

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How to generate and interpret fire characteristics charts for the U.S. fire danger rating system

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The fire characteristics chart is a graphical method of presenting U.S. National Fire Danger Rating System (NFDRS) indexes and components as well as primary surface or crown fire behavior characteristics. Computer software has been developed to produce fire characteristics charts for both fire danger and fire behavior in a format suitable for inclusion in reports and presentations. Scales, colors, labels, and legends can be modified as needed. The fire characteristics chart for fire behavior has been described previously (Andrews et al. 2011). This report describes the fire characteristics chart for fire danger, which displays the relationships among the Spread Component, Energy Release Component, and Burning Index by plotting the three values as a single point. Indices calculated by using FireFamilyPlus can be imported into the fire danger characteristics chart software. Example applications of this software for comparing fire seasons, weather stations, and fire danger rating fuel models are presented.

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Refining the cheatgrass-fire cycle in the Great Basin: precipitation timing and fine fuels predict fire trends

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This study investigated the complex relationships among weather, fine fuels, and fire in the Great Basin, USA. It found that cheatgrass cover increased in years with higher precipitation and especially when one of the previous 3 years also was particularly wet. Area burned in a given year was mostly associated with native herb and non-native forb cover, whereas cheatgrass mainly influenced area burned in the form of litter derived from previous years’ growth. Results suggest that the region’s precipitation pattern of consecutive wet years followed by consecutive dry years results in a cycle of fuel accumulation followed by weather conditions that increase the probability of wildfire events in the year when the cycle transitions from wet to dry. These patterns varied regionally but were strong enough to allow us to model annual wildfire risk across the Great Basin based on precipitation alone.

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Long-term impacts of wildfire on fuel loads, vegetation, and potential fire behavior in sagebrush

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This study showed higher levels of resilience to fire than is typically discussed in the sagebrush steppe, in part because the studied ecosystems were in good condition before the fire, but also because the longer post-fire monitoring time (17 years) may be more appropriate to capture patterns of succession in these ecosystems.

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Computational study of the interactions of three adjacent burning shrubs subjected to wind

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The burnout time for upstream shrubs increased with an increase in shrub separation distance for all shrub sizes and wind speeds considered. The burnout time for the downstream shrub was found to decrease with an increase in the separation distance, reach a minimum, and then increase with an increase in separation distance. The trends observed in burnout times for downstream shrub were attributed to the balance between heat feedback into the downstream shrub from the flames in upstream shrubs and availability of sufficient oxygen for combustion to take place.

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Defining wildland firefighter safety and survival zone separation distances

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The significant variables for the fatal injury model were fire shelter use, slope steepness and flame height. The separation distances needed to ensure no more than a 1 or 5% probability of fatal injury, without the use of a fire shelter, for slopes less than 25% were 20 to 50 m for flame heights less than 10 m, and 1 to 4 times the flame height for flames taller than 10 m. The non-fatal injury model significant variables were fire shelter use, vehicle use and fuel type. At the 1 and 5% probability thresholds for a non-fatal injury, without the use of a fire shelter, the separation distances were 1 to 2, 6 to 7, and 12 to 16 times greater than the current safety zone guideline (i.e. 4 times the flame height) for timber, brush and grass fuel types respectively.

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New technology allows scientists to see the forces behind the flames

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This news story provides some about the history and future of fire behavior research.

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Near-term probabilistic forecast of significant wildfire events for the western United States

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In this study, we present a framework for forecasting large fire occurrence – an extreme value event – and evaluating measures of uncertainties that do not rely on distributional assumptions. The statistical model presented here incorporates qualitative fire danger indices along with other location and seasonal specific explanatory variables to produce maps of forecasted probability of an ignition becoming a large fire, as well as numbers of large fires with measures of uncertainties. As an example, 6 years of fire occurrence data from the Western US were used to study the utility of two fire danger indices: the 7-Day Significant Fire Potential Outlook issued by Predictive Services in the US and the National Fire Danger Rating’s Energy Release Component. This exercise highlights the potential utility of the quantitative risk index as a real-time decision support tool that can enhance managers’ abilities to discriminate among planning areas in terms of the likelihood and range of expected significant fire events.

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Integrating fuels treatments and ecological values in piñon-juniper woodlands: Fuels, vegetation, and avifauna

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This study investigated the effects of mastication and hand-thinning treatments in piñon-juniper (PJ) woodlands on ecological processes including fire, and on a wide range of species, particularly vulnerable PJ obligate birds.  Treatments drove major, persistent ecological shifts relative to controls. Tree cover and canopy fuels were reduced; concomitantly, down woody surface fuels, forb, and grass cover increased. Treatments exhibited rapid, large, and persistent increases in the frequency, richness, and cover of 20 non-native plant species including cheatgrass.  Treatments substantially reduced the occupancy of piñon-juniper specialist and conifer obligate bird species.

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Wildland fire: Nature’s fuel treatment

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This bulletin summarizes the evaluation of more than 40 years of satellite imagery to determine what happens when a fire burns into a previously burned area. Results from this research are helping land managers to assess whether a previous wildland fire will act as a fuel treatment based on the length of time since the previous fire and local conditions such as ecosystem type, topography, and fire weather conditions. By factoring in the ecological benefits of fire, land managers are able to manage fire in a way that fosters more resilient landscapes.

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