Fire Behavior
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This study shows that night-time fre intensity has increased, which is linked to hotter and drier nights. Our findings are based on global satellite observations of daytime and night-time fire detections and corresponding hourly climate data, from which we determine landcover-specific thresholds of VPD (VPDt), below which fire detections are very rare (less than 95 per cent modelled chance). Globally, daily minimum VPD increased by 25 per cent from 1979 to 2020. Across burnable lands, the annual number of flammable night-time hours—when VPD exceeds VPDt—increased by 110 hours, allowing five additional nights when flammability never ceases. Across nearly one-fifth of burnable lands, flammable nights increased by at least one week across this period. Globally, night fires have become 7.2 per cent more intense from 2003 to 2020, measured via a satellite record.
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Respondents were less confident in the accuracy of wind and precipitation forecasts than relative humidity or weather forecasts more generally. The influence of weather information on the decision depended on the framing used in the choice experiment; specifically, whether respondents were told the initial strategy had been to directly or indirectly attack the fire. Across conditions, fire managers generally preferred to indirectly attack the fire. Decisions about the tactics to apply going forward were more sensitive to time in season when the fire was occurring and wind and precipitation forecasts than to other attributes.
Webinar recording.
This 1-hour webinar presents findings from a recently completed study, which was funded by the Joint Fire Science Program, on landscape fuel treatment effectiveness within recent large wildfire events in north-central Washington State. It provides an overview of climate change and wildfires and the imperative for broad-scale adaptive management to increase landscape and community resilience to future wildfires. Then reports findings on the effects of prior fuel reduction treatments, biophysical environment, and weather on fire severity. The study also evaluated fireline effectiveness and how past fuel treatments assisted in safe and effective response.
Webinar recording.
Conflagrations like the 1871 Peshtigo have reemerged as important threats across North America and around the world. Understanding the factors and the phenomena that produced the fire environment of that day is possible because of weather observations collected and recorded at the time and studies of extreme fire behavior that continue to this day. Recounting it should be a cautionary tale for our lives as we continue to live them.
Webinar recording.
Conflagrations like the 1871 Peshtigo have reemerged as important threats across North America and around the world. Understanding the factors and the phenomena that produced the fire environment of that day is possible because of weather observations collected and recorded at the time and studies of extreme fire behavior that continue to this day. Recounting it should be a cautionary tale for our lives as we continue to live them.
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Here, we focus on the elevational distribution of forest fires in mountainous ecoregions of the western United States and show the largest increase rates in burned area above 2,500 m during 1984 to 2017. Furthermore, we how that high-elevation fires advanced upslope with a median cumulative change of 252 m (−107 to 656 m; 95% CI) in 34 y across studied ecoregions. We also document a strong interannual relationship between high-elevation fires and warm season vapor pressure deficit (VPD). The upslope advance of fires is consistent with observed warming reflected by a median upslope drift of VPD isolines of 295 m (59 to 704 m; 95% CI) during 1984 to 2017. These findings allow us to estimate that recent climate trends reduced the high-elevation flammability barrier and enabled fires in an additional 11% of western forests. Limited influences of fire management practices and longer fire-return intervals in these montane mesic systems suggest these changes are largely a byproduct of climate warming. Further weakening in the high-elevation flammability barrier with continued warming has the potential to transform montane fire regimes with numerous implications for ecosystems and watersheds.
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No significant change was projected for the number of human-caused fire ignitions, but we projected a 14% reduction in lightning-caused ignitions under future conditions. Mean fire sizes were 31% and 22% larger under future conditions (2031–2060) for human and lightning-caused ignitions, respectively. All but one climate model projected increased frequency of record-breaking events relative to the contemporary period, with the largest future fires being about twice the size of those of the contemporary period. This work contributes to understanding the role of lightning- and human-caused fires on future fire regimes and can help inform successful adaptation strategies in this landscape.
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The Pack Creek Wildfire, ignited by an abandoned campfire, started early in the fire season on June 9, 2021 in the Pack Creek Day Use Area on the Manti-La Sal National Forest.
Under the influence of down-slope, down-canyon winds, the fire made a push west and down Pack Creek. The fire quickly exploded as a crown fire through a riparian area composed largely of cottonwood trees and pinyon and juniper landscapes. Within the community, fuel breaks implemented by Forestry, Fire and State Lands (State of Utah, FFSL) were designed to act as intermittent catch points for firefighters to actively engage the fire.
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Large wildfires need four key ingredients to burn, not just one. Ignitions, fuels, and drought thresholds must be crossed at the same time, enhanced by anomalous weather events such as foehn winds. But how do these ingredients, or drivers, fit together in various ecosystems? In this important concept paper, Pausas and Keeley (2021) outline the mechanistic flow of these complex drivers for fire prone ecosystems and illustrate this in the figure below (Fig.1). In brief, the fire weather for a given ecosystem helps to push the other three essential driver thresholds, or saturation points, down. With ignitions, fuel continuity, and drought saturation points simultaneously lowered by the right weather, wildfire will be triggered.
WindNinja, a tool developed by RMRS scientists, delivers high-resolution wind predictions within seconds for emergency fire responders making on-the-ground decisions. The program computes spatially-varying wind fields to help predict winds at small scales in complex terrain. These predictions are extremely important in fire-prone landscapes where local changes in the near-surface wind are not predicted well by either operational weather models or expert judgment but are extremely important for accurate fire behavior predictions.