1. Data Science

Climate Change and Wildfires

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Wildfires have been a huge issue in Alaska this year. More than 530 fires have burned an area the size of Connecticut, forcing people to evacuate from mining camps and villages.

The fire season is still going firescout strong, but many of the fires are much bigger and hotter than usual. Climate change, a persistent drought and lightning strikes are all fueling Alaska's fires.
Climate Change

Alaska’s climate has been changing in ways that make it harder for firefighters to protect communities from wildfires. It’s also making fires more frequent, and a greater threat to people and their homes.

The Earth is warming due to global greenhouse gas emissions. These include carbon dioxide from burning gasoline or coal, and methane released when land and forests are cleared for other uses.

Across the globe, hotter temperatures are causing heatwaves and droughts that can dry out vegetation and trigger wildfires. In the Arctic, temperatures are rising faster than in other parts of the world. In Alaska, the number of days with high temperatures above 77 degrees Fahrenheit is expected to double by midcentury, according to the latest climate models.

These trends can lead to more severe and drier fires that are difficult to contain, says Kate Fresco of the University of Alaska Fairbanks. The increased frequency and intensity of lightning strikes, triggered by warmer weather, are a key factor.

There’s another aspect of climate change that could be a major problem for Alaskan fire management: thawing permafrost. Warmer temperatures can make permafrost more vulnerable to thawing and decomposition, which releases carbon from the ground.

In the past few decades, there’s been an increase in reburns of burned tundra areas in Alaska, Fresco said. These reburns can cause soil to thaw earlier than usual, allowing different plants to grow that aren’t normally found there. These changes can be especially harmful to the slow-growing tundra vegetation, she added.

A holdover fire, which smolders in the duff layer under the snow throughout winter and continues to burn in the spring, is also becoming more common in Alaska. These fires are a risk to human health, since they can spread rapidly, according to researchers.

The increasing rate of fire reburns is particularly problematic for the slow-growing tundra vegetation and for the trees that form a transition zone between the tundra and forest. These reburns can accelerate the shift in species composition from coniferous to deciduous trees in Alaska’s boreal forests.

In addition, thawing permafrost can release carbon from the ground, but these post-fire emissions haven’t been included in climate models. Measurements of these emissions rely on long-term field observations, which are difficult to obtain in the Arctic and in remote areas where people are often in danger.
Drought

In recent years, drought has caused fires in Alaska to be much more frequent. In fact, the state has seen the largest wildfires on record (Taylor Complex – 2004, McKinley Wildfire – 2007, and Swan Lake – 2019), and the most expensive fire suppression effort in history (Swan Lake – 2019).

The number of days with temperatures above 77 degrees F, a key threshold for drying out vegetation, is increasing significantly. Climate models project the annual number of days above this temperature to double by midcentury.

Another driver for a worsening fire season in Alaska is warmer winter temperatures that cause less snow to fall as it melts, leading to more dry vegetation and quicker fire growth. Decreased snowpack also increases surface temperatures, which can exaggerate drought conditions and further exacerbate fire risk.

Drought also reduces water availability for fish, salmon and other ecosystems that rely on snowmelt to produce cold water. In addition, it can affect subsistence and fishing communities, preventing people from doing what they love most.

In one of the driest summers in Alaska’s history, 530 wildfires are burning an area the size of Connecticut across southwestern and Interior Alaska, according to the National Interagency Fire Center. The blazes have displaced residents and forced many to evacuate.

As the fires burn, they produce smoke, which is a major concern in the Arctic, where it can limit visibility and lead to respiratory diseases like asthma. Smoke is also a problem in densely populated areas where homes are often not built to withstand smoky conditions.

Earlier this month, residents in Saint Mary’s, a small village on the south shore of Prince William Sound, had to flee their homes when they were hit by a pair of wildfires that spread quickly and pushed smoke into their community. The smoke was so thick that the air quality index at a hospital in Nome, 400 miles away, reached 600 parts per million, an unhealthy level for PM2.5, fine particulate matter that can trigger respiratory problems.

While the fire season is generally over by late September, this year the rains and cooler weather have delayed the fires’ progress. However, long-term forecasts show the same pattern of dry, hot weather and lightning-sparked wildfires as in 2004.
Lightning Strikes

Lightning strikes are a major cause of wildfires, especially in dry climates. These fires can quickly spread depending on weather conditions and fuel availability, and they can release large amounts of carbon, nitrogen oxides and other trace gases into the air.

Alaska is facing a very early and significant wildfire season this year, thanks to warmer temperatures and thousands of lightning strikes across the state. This is a trend that has fueled numerous fires, including the Lime Complex, one of the largest wildfires in the state.

By mid-June, more than 250 wildfires have already burned more than 770,000 acres, not counting prescribed burns. That's far more than the 30-year median of 600,000 acres burned in a typical wildfire season.

Longer-term forecasts show the usual worst of the season lays ahead, with July rains giving way to high-pressure systems, hot days and low humidity, like those that led to a devastating fire year in 2004. That means more fires and the usual challenges of containing them – particularly in the southwestern tundra region where there are few flammable resources.

But even that hasn't stopped the blazes from consuming a huge area, and in some places they're burning for weeks. In the case of the Swan Lake Fire, which started in June of 2019, it burned until October and consumed 167,000 acres.

The smoke from these fires can also deteriorate air quality, particularly in urban areas. In early July, a pair of wildfires in Southwest Alaska joined, and the dense smoke from the two fires blew hundreds of miles north to Nome, where the air quality index at the hospital there exceeded 600 parts per million for PM2.5, fine particulate matter that can trigger asthma and harm the lungs.

And the influx of heavy smoke is also making it more difficult for firefighters to do their jobs. Smoke can make it harder to see, while it's also more likely that people will have to leave if the fire spreads to their homes and threatens their health.

The threat of fires is becoming a bigger issue in Alaska, and the risk is getting worse with every passing year. The average number of days above 77 degrees F in the state's interior is expected to double by midcentury, according to the latest climate models. That's a key temperature threshold that can help prevent fire growth. But the warming climate has exacerbated droughts and heat waves, making fires more likely to grow, spreading and burning for longer periods of time.
Vegetation

Fires burn a great deal of vegetation. They also destabilize the soil and permafrost that have accumulated over centuries, releasing huge amounts of carbon from these natural stores.

Wildfires are now occurring at record rates, with large blazes ravaging communities across the United States and Europe. This is due to warmer temperatures and drier conditions that increase fuel loads and make fires more likely.

While some of the vegetation that fuels these fires is naturally fire resistant, others cannot be controlled. Some trees, for instance, can grow thicker and taller than they would if left unburned, making them easier to ignite.

These changes in the landscape can alter how quickly a fire spreads, how hot and how intense it is. That can impact the lives of those who live, work and play in a given area, as well as those who come to enjoy the outdoors.

One example of this is the East Fork fire in Western Alaska, which has now burned more than 150,000 acres in an area that only saw a few such fires before, according to climate specialist Rick Thoman at the University of Alaska Fairbanks' International Arctic Research Center. It's the largest tundra fire on record, and it's being driven by climate change.

Historically, the boreal forest in Alaska is relatively stoically fire-resistant and regenerative after fire. However, recent climate trends are increasing the frequency of short-interval fires in the boreal forest and changing broadleaf communities to a greater extent than before.

Researchers are trying to understand the potential effects of these fires on ecosystems, especially with respect to vegetation and soil. These impacts can include increased temperature, soil thawing, changes in species composition and the loss of permafrost.

The most dramatic effect of these fires, however, may be on the soil itself. In summer, when the charred black surface of a fire allows air to get hotter and moisture to evaporate more easily, soil can heat up. This can affect soil depth and potentially change the nutrient content of the soil, affecting plant growth.

The resulting changes in soil composition can lead to an increase in the growth of grasses and shrubs. These can outcompete slower-growing mosses, lichens and dwarf shrubs. This can be detrimental to the health of the surrounding forests.

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