Wildfire smoke increasingly travels thousands of miles, sometimes across the entire country. Get a rundown of the latest wildfire-smoke science, opportunities to mitigate it, and tools to communicate about it in the blog post below. Photo: Smoke from 2017 California wildfires spanning the U.S. Credit: NASA

How Healthier Forests Can Mean Less Smoke: The Science, Tools and Strategies Related to Smoke Management in Fire-Adapted Forests

By: Dr. Leland Tarnay, USDA Forest Service Region 5 Remote Sensing Lab

Topic: Communications / Outreach Fuels treatment / Prescribed fire Wildfire

Type: Research Synthesis

The Air Quality Problem

With disconcerting regularity, smoke from large wildfires keeps saturating the skies of California (and other states) for days on end, over vast swaths of our otherwise sunny state. When that dense smoke spreads regionally and covers large urban areas, millions of people are potentially affected. Satellite mapping shows that dense areas of smoke can span county, state and even continental scales — living in an area far removed from a forest is no longer a guarantee that you won’t have to deal with wildfire smoke. How has this come to pass, and what can we do about it?

Two different maps of California showing smoke in different ways

Left: A smoke plume from the Rim Fire, on a day when high-density smoke reached more than 2 million people in California and Nevada. Note that it traveled to three other additional states as well that day. Credit: Long et al. (2017). Right: The total number of days with any smoke plumes (by county, in California) from May 1 through Sept. 30, 2015. Credit: Wettstein et al. (2018)

The Landscape Problem: Too Much Fuel, Burning Too Fast

As most fire practitioners know, the root of this problem is a dry, fire-adapted landscape, far-perturbed from its equilibrium by past fire suppression, which has homogenized whole landscapes with uniformly dense fuels (North et al., 2009). With the right alignment of fuels, fire and terrain, such landscapes can and have been literally exploding with rapid fire growth, releasing thousands of tons of fine particles in a single day, and saturating the atmosphere with “waves” of smoke at regional scales (Liu et al., 2016; Long et al., 2017).

A photo of an overly dense forest next to a forest with trees that are more spaced out

A side-by-side comparison of a fire-suppressed stand in the Teakettle Experimental Forest (left) versus a mixed conifer stand in Yosemite National Park that is maintained by frequent, low-intensity fire (right). Click on the image above to access more information about forest structure and the effects of fire suppression on fuels. Credit: Malcolm North, USDA Forest Service

In the most destructive (high severity) fires, like the 2013 Rim Fire in and around Yosemite National Park, entire stands of trees were killed and are growing back as uncharacteristically large patches of shrub that have extremely high fuel loading due to dead and down trees that were killed (Stephens et al., 2018). A decade or two later, these areas can burn again at high severity, creating an even larger patch of uncharacteristically homogeneous fuel, emitting thousands of tons of fine (PM2.5) particulates in the air, every day (Lydersen et al., 2014 — PDF, 1.9MB; Long et al., 2017).

A map of the Rim Fire footprint, displaying the various levels of smoke pollution (in tons of PM2.5/day)

The 2013 Rim Fire “flooded” the atmosphere with thousands of tons of PM2.5; these daily emissions were orders of magnitude more than the daily emissions typical of less severe, slower moving fires (like prescribed fires and wildfires being managed for resource objectives). Note that this particular fire is flanked to the south and east by areas previously exposed to prescribed fires and/or managed wildfires. Credit: Long et al. (2017)

Author’s note: Just as I was writing this post, the Ferguson Fire began in Sierra National Forest, outside of Yosemite National Park, making the work of two recently managed wildfires even more clear. The 2009 Grouse Fire (referred to in the Long et al., 2017 paper discussed above and shown as a green polygon in the figure above) was critical in stopping the Ferguson Fire. After the Ferguson Fire came out of Indian Canyon with a large plume driving it, it blew across the Wawona Road and Glacier Point Road. Crews were unable to construct the fireline, and one more day of winds (and ventilation) was predicted. We were preparing for the fire to enter Yosemite Valley,  which would have entailed another four weeks of active fire and multiple additional closures. However, the Ferguson Fire found its way to the Grouse and Avalanche Fire footprint, where it laid down. Crews were then able to make substantial progress and contain the fire. 

Landscape Strategies that Limit Daily Smoke Production

In the decades leading up to the Rim Fire, Yosemite National Park adopted a proactive fire management stance, implementing larger-scale prescribed fire and managing naturally ignited wildfires for resource objectives where and when appropriate. In the Tuolumne Drainage, one of the major goals of that work was to impede and help contain a potential large-scale fire that might one day push into the park from lower elevations. Prescribed fires and naturally ignited wildfires that occurred in an area that could catch such a fire were prioritized, forming a large-scale “catcher’s mitt” across the Tuolumne Drainage.

In August 2013, that scenario became a reality, and this catcher’s mitt strategy slowed the Rim Fire enough to allow firefighters to create and defend a landscape-scale containment line that was several miles long and was incorporated into previous wildfire and prescribed fire footprints. (See the 2013 Rim Fire map above.) Without those previous fires and treatments in place, the incident management teams would have had to construct their own line further up the drainage, likely leading to thousands of additional acres burned and even more weeks of smoke impacts.

Recent research (again, see Long et al., 2017) shows that while the proactive fire management in the decades leading up to the Rim Fire did produce some smoke, those emissions were far lower on a daily basis than almost every day during the Rim Fire, and the impacts were correspondingly much less intense.

A bar graph showing that the average daily emotions for the fires in this study were much lower when the fire was either prescribed or managed for resource objectives than typical wildfires. Megafires were about 20 times greater than typical wildfires.

The average daily emissions (measured in metric tons of PM2.5/day) of different fire types during a 10-year analysis of fires in the Yosemite National Park area. Credit: Jonathan Long, adapted from Long et al. (2017)

It’s a good trade-off, and a more air-quality-friendly way to “re-enter” a landscape without necessarily burning it entirely, if the treatments are appropriately sized, and strategically placed and timed.

A Climate Problem “Piling” on Top of the Fuels Problem

California’s climate is warming, especially in the Sierra Nevada, and that rate of warming is accelerating.

A bar graph showing that California's statewide mean temperature is getting higher and higher than the historical average as time passes

This graph displays the difference between the mean statewide temperature from 1949–2005 and individual years since 1900. Note the accelerating positive difference. Check out the California Climate Tracker by clicking on the graph above; it is a powerful tool that is regularly updated and gives users the latest climate data. Credit: Western Regional Climate Center

This warming has profound implications for both emissions and smoke impacts for communities. Liu et al., 2016 showed that based on climate models, exposure to smoke will likely increase and spread in the next 30 or so years, due to increased fire activity.

Two maps of the western United States, showing an increase in smoke risk over time

Map a: The Fire Smoke Risk Index from May to Oct. 2004–2009. Map b: The Fire Smoke Risk Index from May to Oct. 2046–2051 (using climate models). Models show an increase in risk over the next 30 or so years, shown by the increase in red and orange from Map a to Map b. Credit: Liu et al. (2016)

It should be noted that Liu et al.’s scenario doesn’t necessarily account for the further accumulation of fuels, which might exacerbate these trends.

Landscape Mosaics as a Longer-Term Strategy

The Rim Fire “catcher’s mitt” illustrates a scenario in which a drainage was at least partially protected against megafire, but what happens after that fire on the larger landscape and in the long term? Just one drainage over from the Rim Fire, in the Illilouette Basin, Collins et al. (2009) showed that the footprint of one fire can limit the spread of subsequent fires, especially in areas that burn at low to moderate severity, where the wildfire essentially acts like a fuels treatment.

Even if a previous fire doesn’t stop the subsequent fire, Lydersen et al. (2017, PDF, 1.9MB) and Taylor et al. (2017) showed that areas recently burned by low to moderate severity fire re-burned at similarly low to moderate severity. On the other hand, areas that had burned at high severity preceding the Rim Fire burned at similarly high severity, with the size of those high severity patches expanding. In other words, high severity wildfire begets more high severity, and low to moderate wildfire severity tends to generate more low to moderate severity. In this way, each new low to moderate severity fire becomes a potential anchor that could be used to limit the spread, moderate severity, and potentially lower the daily smoke emissions of a subsequent fire.

More Smoke, but How Much More?

Even with large investments in fuel treatments, it will likely take decades to reverse the impacts of 100 years of fire suppression. In the meantime, there will likely be more smoke — there is no “no fire” scenario in these dry forest ecosystems. However, Hurteau et al. (2014) showed that we may have some choices about how much smoke, even if you account for the increased fire we’ll see due to a warming climate. Their modeling exercise calculated emissions under cooler, less extreme conditions which occur in the spring and fall, and compared those emissions to “business as usual” high severity emissions under the hot, dry, midsummer conditions. They found that total emissions can be reduced substantially (by as much as half) by prioritizing lower severity fire. In some cases, that’s a difference of thousands of tons of smoke.

Investing in Pace and Scale

Adopting a more proactive fire management stance in more of California’s forests will require substantially more money, human capital and social license to burn (which may be higher than we think in some areas). Through the Fire MOU Partnership, a novel partnership among federal, state and local agencies, momentum is building for such an investment. Just a few months ago, the governor of California released the California Forest Carbon Plan (PDF, 8.7MB), which allocates $96 million to support the implementation of the plan. This is in addition to the $160 million proposed in January’s Cap and Trade expenditure plan (PDF, 352KB) to support forest improvements and fire protection.

Monitoring, Modeling and Messaging

Given that there will be more smoke, how do we minimize those public health impacts and empower the public with useful information regarding what to do about it? In California, a good chunk of the Forest Carbon Plan funds is being earmarked to help air quality and fire managers monitor, predict and communicate about smoke, using a monitoring, modeling and messaging framework.

For years now, the U.S. Forest Service Pacific Northwest Research Station’s AirFire Team has consolidated the tools to support this monitoring, modeling and messaging framework in one place, online. This portal integrates custom tools needed to create the best possible predictions about where and how unhealthy the smoke will be, based on currently deployed monitoring and smoke dispersion modeling. Research has shown that media messaging that doesn’t incorporate such tools can often be wrong (Cisneros et al., 2018; PDF, 710KB), but if actual data from models and monitoring are used to predict and warn people about when and where smoke impacts will occur, measurable public health benefits can be achieved (Rappold et al., 2014).

Interpreting modeling and monitoring data into a coherent, consistent message requires expertise and experience. During the largest wildfires, incident management teams often now employ air resource advisors (ARAs) on wildfires as part of the Wildland Fire Air Quality Response Program.

An air resource advisor adjusting smoke monitoring equipment

Air resource advisors are trained technical specialists who assist with understanding and predicting smoke impacts during a wildfire. They analyze, summarize and communicate these impacts to incident management teams, air quality regulators and the public. Credit: USDA Forest Service

These ARAs are trained to use and interpret the AirFire tools for predicting when, where, and how intense smoke is likely to manifest, but these tools can also be used by public officials, fire management staff, and others with the responsibility of informing the public about the timing and location of potential smoke episodes, both for prescribed fire and for wildfire. AirFire tools inform the daily one-page summaries for large fires and give people timely information for minimizing their smoke exposure (like this one generated recently during the Ferguson Fire; PDF, 248KB).

Screengrabs from Airfire

The AirFire monitoring site aggregates data from all of the agencies monitoring the smoke from fires, nationwide, as part of the Wildland Fire Air Quality Response Program. The tools help translate smoke data into easily understandable metrics for overall air quality (e.g., the Daily AQI), and shorter-term, hourly metrics (e.g., Hourly Nowcast) that are useful for avoiding the worst of the day’s smoke. Click on the image above to access AirFire’s interactive map and produce similar looking graphs as shown above. Credit: Airfire

Used in concert with the operational BlueSky modeling, the BlueSky Playground (USFS login required) and myriad portable smoke monitors available from local and state air pollution agencies, these tools are intended to help fire and air quality managers provide the best available information to the public about when and where the smoke will be, and how to avoid it.

Balancing Smoke Exposure with Activity

Although the Air Quality Index (AQI) provides general guidelines to gauge air quality, everyone’s sensitivity to smoke is different, and even one person’s sensitivity to smoke can vary or change over time. Thus, the AirFire tools are publicly available and can empower local public health officials and individuals to make the best choices for themselves, making adjustments to their activities, like we would do with rain, wind or other environmental disturbances.

Two "balance beams" of activity and smoke, with two different fulcrums.

When it comes to wildfires, smoke is often highly variable over the course of a given day. For more sensitive people, balancing smoke avoidance with activity will mean going inside as soon as hourly levels reach “moderate,” and then coming back out again once levels recover to the “good” range. For other less sensitive/more active individuals, it may be OK to stay outside longer, especially if they spend the rest of the day breathing clean air. Advice on how to tell when smoke is affecting you can be found by clicking the image above. Credit: Dr. Leland Tarnay

One of the keys to avoiding smoke is creating cleaner indoor environments to which you can escape (and knowing when to do so). We build houses to keep out rain, and we can also build them to keep out smoke by using heat and cooling systems that limit the amount of outside smoke coming into a home. If it’s too expensive to retrofit your house, there are inexpensive ways to establish clean rooms (PDF, 820KB), especially the ones where people spend the most time. More fact sheets on how to avoid smoke and prepare for smoke season are available online.

Putting it All Together

Smoke waves in California alone are affecting the hearts (and lungs) of millions of people, in nearly every part of the state (and also many people living in other states). Further, this is happening in fire-adapted forests throughout the West, and affecting air quality throughout the entire continent. As I write this, for example, even people in New York were getting smoke from California. The megafires creating this smoke are also potentially homogenizing more of acres of forest, which may create even more smoke waves in the future, all while a warming climate likely magnifies these trends.

Recent megafires have also forced those of us who work in the air and land management fields to work more closely together than ever, across all agencies, jurisdictions and landscapes. As a result, we are at a pivotal moment in the history of smoke management, where we have built regional-scale tools and interagency expertise to more proactively manage our fire-adapted landscapes and minimize public health impacts holistically. If we can break up the fuels in these landscapes and re-establish fire mosaics in the coming decades, we might have a shot at heading off the worst of the air quality-related consequences.

Portrait image of Lee, with wildfire smoke in the background

Credit: Dr. Leland Tarnay, USDA Forest Service

Dr. Leland (Lee) Tarnay is an ecologist working for the USDA Forest Service Region 5 Remote Sensing Lab. Lee received his Bachelor of Science in Biology from the University of California, Davis (1995), and his Ph.D. from the University of Nevada, Reno (2001). He spent 10 years as Yosemite National Park’s air resource specialist before joining the Forest Service. While he is most interested in interactions between land and the atmosphere, and the implications of those interactions for land managers, his current core expertise is in smoke monitoring, emissions estimating, dispersion modeling, and mapping forest fuels and structure. When he’s not with his family, mountain biking, or skiing in the forests he loves, Lee is helping land management agencies increase the pace and scale of good fire while minimizing smoke impacts.

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