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Alaska's Changing Wildfire Environment
An intensified pattern of wildfire is emerging in Alaska as rapidly increasing temperatures and longer growing seasons alter the state's environment. Both tundra and boreal forest regions are seeing larger and more frequent fires. The impacts of these fires are felt across the state.
The wildland fire environment of Alaska presents many unique opportunities and challenges. In response to changing wildfire patterns, Alaska's fire management agencies are adapting quickly. The use of remote sensing tools, such as data from satellites, and science-based decision making have been a critical component in responding to intensified wildfire seasons.
Here, we communicate the rapidly changing patterns of wildfire in Alaska by looking into the phases of fire. Patterns emerging in the 21st century are the primary focus, with earlier histories of management, climate, and fire being drawn upon for context.
The Alaska Fire Science Consortium strives to increase understanding of the critical role of wildfire within the state, by facilitating science delivery, outreach, and education.
- Wildfire is a natural process in Alaska, and more acres are burning as the climate warms.
- Alaska’s fire environment is vast, complex, and unique.
- Managing wildland fire in Alaska requires advanced planning and cooperation among many agencies.
- Fire management relies on science to effectively plan and implement fire suppression efforts.
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Alaska’s rapidly changing climate profoundly impacts the state's ecosystems and fire regimes. Earlier snow melt, later winters, higher temperatures, more frequent lightning strikes, and changing vegetation are altering Alaska's fire environment.
Temperatures in the Arctic are rising at twice the average rate globally. The annual average Arctic surface air temperature rose by 4.9°F from 1971 to 2017, with five of the hottest years ever recorded occurring from 2014–2019.
The Alaska fire season, particularly in the interior region of the state, has four phases. Early fire season, just after snow melt, is typically driven by dead grass ignited in human activities and spread by wind.
The peak of the fire season is driven by long warm days around solstice, which dry out subsurface fuels (known as duff) that can then be ignited by lightning. Later in July, if temperatures remain high and precipitation is low, drought may extend and expand the fire season. Finally, as the season winds down in fall, the cooler nighttime temperatures normally slow fire activity.
Spring fire: wind
Fire season begins in April, typically before full green-up when the below ground soil is still frozen. The most readily available fuels are dead grasses and surface litter. With these limited fuels, wind is the key driver of fire activity.
Fire can spread and grow rapidly, but usually with low severity because it cannot burn deeply into the moist and frozen duff. Early season fire is often the result of human-caused ignitions when outdoor recreation activities and debris burning lead to unintentional fire starts. These preventable fires are usually close to human communities and receive aggressive suppression response.
Peak season: duff
In northern latitudes, a surface layer of slowly decomposing moss, lichen, and litter, called duff, is often about a foot deep. Duff in boreal and tundra landscapes generally accounts for more biomass below ground than available above ground. This duff layer creates a unique fuel bed where wildfire can burn deep below the surface and smolder for days or weeks, reigniting fuels at the surface when weather conditions become favorable.
Fire activity may greatly increase in June as long sunny days quickly dry out duff fuels. Dry duff fuels easily spread fire and can make burns difficult to control. This duff-driven phase of the fire season is typically when peak fire activity occurs.
Lightning and peak fire season
Lightning is most common during the duff-driven phase. In most years, and all years with a substantial fire season, the majority of acres burned are caused by lightning ignitions. These fires are often in remote locations where managers can allow fires to serve their ecological role without directly impacting human life or property.
Human-caused wildfires tend to occur closer to communities, are suppressed quickly, and occur earlier in the year than fires ignited by lightning. In many years, the total number of fires caused by humans is greater, and require more resources to fight than the number of fires started by lightning.
Late summer: drought
As lightning diminishes toward the end of July, fewer fires are ignited. Existing fires may grow during the drought-driven stage of the fire season if late summer rains are sparse. Fires during extreme drought can be difficult to extinguish and may even result in fires burning underground through winter.
Fire season in Alaska is typically pushed to a close by shorter days with lower solar radiation. As nighttime temperatures drop and relative humidity increases, fire has difficulty spreading. The past two decades, however, have included notable late-season fire events related to relatively high temperatures and low precipitation in August.