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Although an increase in the frequency of large-fire seasons has been observed over the last couple decades concurrent with increases in temperature over Alaska, our results suggest that extrapolation on the basis of projected warming might fail to account for the processes involved in fire ignition and growth. A comprehensive approach to predicting future wildfire potential in Alaska should attempt to account for factors that contribute to ignition potential (e.g. critical DMC [Duff Moisture Code] indices), ignitions (lightning- and human-caused) and fire growth in addition to the dynamic vegetation response to climate change and a host of climate-change-assisted disturbance mechanisms (e.g. fire, insects). The prior three factors suggest the need to incorporate high-frequency meteorological conditions into modelling considerations that might be otherwise muted in approaches that only use monthly data. Furthermore, models based on historic relationships relative to fixed calendar days also build in an assumed stationarity of the timing of fire season.
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Management Options
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Forests and Ecosystems
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Wildfire Trends
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R10: Alaska
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From an operational perspective, our results suggest that in-season weather, particularly prolonged dry spells, is critically important in determining the fire growth in Alaska. These findings support the active monitoring of fire danger indices in conjunction with short-range, deterministic weather forecasts and ensemble medium-range forecasts by operational fire management. Recent efforts have focussed on using antecedent climate information for long-range forecasting of fire season. Although processes may link antecedent conditions to other factors involved with fire activity, predictive linkages between the memory in the climate system (i.e. sea-surface temperatures, sea ice, land surface conditions) and conditions favourable to fire growth (e.g. blocking) remain elusive.
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R10: Alaska
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Although the influence of antecedent conditions on fire size [in interior Alaska] was shown to be negligible, post-ignition weather conditions were shown to differentiate between large and small fires. Large fires were enabled by prolonged warm and dry periods that endured several weeks following ignition as a consequence of persistent large-scale blocking, whereas sufficient precipitation to reduce fire growth typically occurred within a week after ignition in the case of small fires. These results suggest that the frequency and timing of significant precipitation events, rather than monthly temperature or monthly precipitation amount, are critical determinants of large wildfires in Alaska. For example, the third largest wildfire season on record occurred in 2005 (1.8 million ha burned) in Alaska and was marked by an anomalously wet period in July across the interior. Extended dry periods in June and again from late July into August allowed for two windows of large wildfire growth (with 32 fires in the large-fire class).
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Forests and Ecosystems
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Wildfire Trends
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R10: Alaska
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Although antecedent conditions were not found to be an important factor for fire growth [in interior Alaska], they may be important in other processes behind seasonal fire activity. We hypothesise that anomalously warm conditions in May–June act either to exacerbate snowmelt and the seasonal drying of fine fuels (e.g. grasses) and the duff layer, thus increasing ignition efficiency (e.g. Jandt et al. 2005), or to decrease atmospheric stability and provide conditions conducive to increased lightning ignitions.
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Forests and Ecosystems
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R10: Alaska
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Previous studies (e.g. Duffy et al. 2005) have shown a strong relationship between antecedent and in-season temperature and area burned in [interior] Alaska. Results from the present study support these findings to the effect that wildfires in the ALFD [Alaska Large Fire Database] occur preferentially during years with anomalously warm May– August temperatures. However, our results suggest that antecedent conditions have negligible influence in determining the growth and eventual area burned by individual wildfires (e.g. Figs 2, 3), and thus our findings can be considered complementary to the findings of Duffy et al. (2005).
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Forests and Ecosystems
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R10: Alaska
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v3.2
