By 2050, the US wildfire season will be three weeks longer, up to twice as smoky

August 18, 2016 by Caroline Perry
By 2050, the U.S. wildfire season will be three weeks longer, up to twice as smoky
Firefighters are currently battling dozens of fires in at least 11 states. Credit: National Park Service

Research by environmental scientists at the Harvard School of Engineering and Applied Sciences (SEAS) brings bad news to the western United States, where firefighters are currently battling dozens of fires in at least 11 states.

The Harvard team's study suggests that by 2050, wildfire seasons will be about three weeks longer, up to twice as smoky, and will burn a wider area in the western states. The findings are based on a set of internationally recognized climate scenarios, decades of historical meteorological data, and records of past activity.

The results will be published in the October 2013 issue of Atmospheric Environment.

Awareness is building that gradual climate change may contribute in the coming years to increases in significant, disruptive events such as severe storms and floods. Loretta J. Mickley, a senior research fellow in atmospheric chemistry at SEAS and co-author of the new study, is thinking one step further, to secondary effects like forest fires and that rely heavily on meteorological factors.

"We weren't altogether certain what we would find when we started this project," Mickley said. "In the future atmosphere we expect warmer temperatures, which are conducive to fires, but it's not apparent what the rainfall or relative humidity will do. Warmer air can hold more water vapor, for instance, but what does this mean for fires?

"It turns out that, for the western United States, the biggest driver for fires in the future is temperature, and that result appears robust across models," she added. "When you get a large temperature increase over time, as we are seeing, and little change in rainfall, fires will increase in size."

By 2050, the U.S. wildfire season will be three weeks longer, up to twice as smoky
A graphic depicts the projected increase of fires in the western United States by 2050. Credit: Xu Yue

Reaching that conclusion with statistical confidence required months of analysis, because at the local level, wildfires are very difficult to predict.

"Wildfires are triggered by one set of influences—mainly human activity and lightning—but they grow and spread according to a completely different range of influences that are heavily dependent on the weather," said Xu Yue, the lead author. "Of course, when all the factors come together just right—whoosh, there's a big fire."

By examining records of past weather conditions and wildfires, the team found that the main factors influencing the spread of fires vary from region to region. In the Rocky Mountain forest, for example, the best predictor of wildfire area in a given year is the amount of moisture in the forest floor, which depends on the temperature, rainfall, and relative humidity that season. In the Great Basin region, different factors apply. There, the area burned is influenced by the relative humidity in the previous year, which promotes fuel growth. Yue, who was a postdoctoral fellow at Harvard SEAS and is now at Yale University, created mathematical models that closely link these types of variables—seasonal temperatures, , amount of dry fuel and so forth—with the observed wildfire outcomes for six "ecoregions" in the West.

After developing those models, the team replaced the historical observations with data based on the conclusions of the fourth Intergovernmental Panel on Climate Change (IPCC), which used socioeconomic scenarios to predict possible future atmospheric and climatological conditions. For this study, the Harvard group followed the A1B scenario, which considers the climatological effect of a fast-growing global economy relying on a mixture of fossil fuels and renewable energy sources. By running the IPCC's climate data for 2050 through their own fire prediction models, the Harvard team was able to calculate the area burned for each ecoregion at midcentury.

The calculations suggest the following for 2050 in the western United States, in comparison to present-day conditions:

  • The area burned in the month of August could increase by 65 percent in the Pacific Northwest, nearly double in the Eastern Rocky Mountains/Great Plains regions, and quadruple in the Rocky Mountains forest region.
  • The probability of large fires could increase by factors of two–three.
  • The start date for the fire season could be earlier (late April instead of mid-May), and the end date later (mid-October instead of early October).
By 2050, the U.S. wildfire season will be three weeks longer, up to twice as smoky
“When you get a large temperature increase over time, as we are seeing, and little change in rainfall, fires will increase in size," said researcher Loretta J. Mickley. Credit: Yale University

Air quality is also projected to suffer as a result of these larger, longer-lasting wildfires. Smoke from wildfires is composed of organic and black carbon particles and can impede visibility and cause respiratory problems. The U.S. Forest Service keeps a record of the amount of fuel (biomass) available across the entire United States, and another set of databases known as the Landscape Fire and Resource Management Planning Tools tracks specific types of vegetation for each square kilometer of land. Based on this information and known emission factors for combustion, the researchers predict that smoke will increase 20–100 percent by the 2050s, depending on the region and the type of particle.

The main innovation of the new study is its reliance on an ensemble of climate models, rather than just one or two. One of the greatest uncertainties in the science of climate change is the sensitivity of surface temperatures to rising levels of greenhouse gases.

"Our use of a multimodel ensemble increases confidence in our results," said principal investigator Jennifer A. Logan, a recently retired senior research fellow at Harvard SEAS.

The fire prediction model developed by the team performed least well in central and southern California, where the rugged topography results in a patchwork of ecoregions, each with a different fire response to changing meteorology. The authors have been investigating the unusual factors at play in that state and expect to release their findings shortly.

For Harvard's atmospheric scientists, the goal of this project was to see how could affect air quality, given that smoke from wildfires is a major source of particulate matter in the atmosphere.

Air quality has vastly improved over much of the United States in the past 40 years, as a result of government efforts to regulate emissions. Mickley warned that increasing might erase some of the progress.

"I think what people need to realize is that embedded in those curves showing the tiny temperature increases year after year are more extreme events that can be quite serious," she said. "It doesn't bode well."

Explore further: Wildfires projected to worsen with climate change

More information: Xu Yue et al. Ensemble projections of wildfire activity and carbonaceous aerosol concentrations over the western United States in the mid-21st century, Atmospheric Environment (2013). DOI: 10.1016/j.atmosenv.2013.06.003

Related Stories

Wildfires projected to worsen with climate change

August 28, 2013

Research by environmental scientists at the Harvard School of Engineering and Applied Sciences (SEAS) brings bad news to the western United States, where firefighters are currently battling dozens of fires in at least 11 ...

Fire seasons are becoming hotter, drier and longer

July 26, 2016

The fast-moving brush fire tearing through the Santa Clarita Valley this weekend is part of a larger trend: Wildfire seasons in the western United States are lasting longer and burning more land, according to a recent report ...

El Nino could drive intense season for Amazon fires

June 29, 2016

The long-lasting effects of El Niño are projected to cause an intense fire season in the Amazon, according to the 2016 seasonal fire forecast from scientists at NASA and the University of California, Irvine.

Recommended for you

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Shootist
1 / 5 (3) Aug 18, 2016
By 2050, the US wildfire season will be three weeks longer, up to twice as smoky


Climate Change©. Is there nothing it cannot do?

Truly a magnificent fraud perpetrated upon all of mankind. Worse that Non-GMO, worse that Gluten free, worse that Organic.
EyeNStein
1 / 5 (1) Aug 18, 2016
A huge water pipeline from the flooding prone southern states and semi-snow-capped northern states to lakes in the dustbowl and fire prone states seems a good idea. Should be achievable before 2050.
aksdad
1 / 5 (1) Aug 18, 2016
Hopefully the results of this study will be published in October 2016, not October 2013 :-)

They arbitrarily picked the A1B scenario which predicts an estimated 2.8° C warming over the 1980-1999 average by 2090-ish (range of 1.7° to 4.4° C). A couple problems:

The computer models aren't accurate. How bad? This bad:

https://www.ipcc....S-14.jpg

Even the lowest estimates are higher than actual warming and get worse with each passing year. The A1B scenario is in the middle of the pack of projections, so even warmer than the lowest (B1) scenario. The 1980-2015 temperature trend is about 0.13° C per decade or about 1.3° C by 2090-ish, obviously much less than A1B.

https://www.ipcc....-of.html

I'll go out on a limb and predict the U.S. wildfire season will be a lot less severe than this study finds.
antigoracle
1 / 5 (3) Aug 18, 2016
I had a glimpse of the past in the AGW Cult's CO2 filled magical crystal ball, it showed how prior to humans there never were any forest fires.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.