Researchers evaluate connection between California wildfires and human-caused climate change

A group of seven scientists published a paper last month that looks at the connection between California wildfires and human-caused climate change, titled Observed Impacts of Anthropogenic Climate Change on Wildfire in California. One of their main conclusions was that climate warming dries the atmosphere which in turn dries fuels, promoting forest fires in the summer.

Here is the abstract:

“Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful.

“Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California’s diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.”

An illustration from the paper:

Climate change California wildfires
Seasonal and annual burned areas in California for 1972–2018. (a) Total burned area in the four regions of focus: (b) North Coast, (c) Sierra Nevada, (d) Central Coast, and (e) South Coast. Annual burned area is decomposed into that which occurred in January–April (green), May–September (red), and October–December (orange). Significant (p < 0.05) trends are shown as bold black curves.

Below is an excerpt from the paper:

“In this study we evaluated the various possible links between anthropogenic climate change and observed changes in California wildfire activity across seasons, regions, and land cover types since the early 1970s. The clearest link between California wildfire and anthropogenic climate change thus far has been via warming‐driven increases in atmospheric aridity, which works to dry fuels and promote summer forest fire, particularly in the North Coast and Sierra Nevada regions. Warming has been far less influential on summer wildfire in nonforest areas. In fall, the drivers of wildfire are particularly complex, but warming does appear to enhance the probability of large fall wildfires such as those in 2017 and 2018, and this effect is likely to grow in the coming decades.

“Importantly, the effects of anthropogenic warming on California wildfire thus far have arisen from what may someday be viewed as a relatively small amount of warming. According to climate models, anthropogenic warming since the late 1800s has increased the atmospheric vapor‐pressure deficit by approximately 10%, and this increase is projected to double by the 2060s. Given the exponential response of California burned area to aridity, the influence of anthropogenic warming on wildfire activity over the next few decades will likely be larger than the observed influence thus far where fuel abundance is not limiting.”

Observed Impacts of Anthropogenic Climate Change on Wildfire in California.
A. Park Williams John T. Abatzoglou Alexander Gershunov Janin Guzman‐Morales Daniel A. Bishop Jennifer K. Balch Dennis P. Lettenmaier
First published: 15 July 2019

Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire. Google+

10 thoughts on “Researchers evaluate connection between California wildfires and human-caused climate change”

  1. Recently, I was asked to provide some key points regarding the wildfires situation. A few of these included:

    1. Large, high intensity wildfires throughout America – especially in the west – have created a national crisis.
    2. The three primary reasons for this national crisis are:
    a. Lack of forest management.
    b. The expansion of the Wildland-Urban Interface [WUI].
    c. The impacts of a changing climate.
    3. Raking leaves won’t get it done. But aggressive forest management will [ensure effective fire management].

    On item No. 2, above, some will suggest a rearrangement of a, b, and c as to their importance. That’s fine. While I appreciate the really good science-based work by these scientists, we know that the impacts of a changing climate is a force on this national crisis. I do not think it’s the primary culprit, but frankly who cares? We have a national crisis and it is time to do something about it.

    America’s forests are in decline. We need an unprecedented national commitment to aggressively manage these forests so eventually wildfires will become less destructive. No more talking. No more studying. We need leadership, resources, and action — now.

    1. Michael,

      The primary hindrance to any large-scale effort to actively manage wildlands is funding. Both Congress and the current and past administrations of both political parties have prioritized other budget items (e.g. defense, health care, etc.) over natural resource management of any kind. This isn’t going to change because there isn’t the collective political will to do anything concrete about it at the scale needed. It’s the same problem with addressing climate change — we know it’s happening, we know it’s going to get worse and yet we continue to refuse to do anything substanstial to address the problem at the level required.

      We keep hoping the problems will go away on their own or that someone else will handle (i.e. pay for) it. Or that it just doesn’t get too bad before it isn’t our problem anymore.

      1. Yes, as I have noted so many times before, a key problem is lack of available resources. Perhaps you have seen the following from me:

        “…Recently, I was reviewing the Forest Service budget. I listed [from my perspective] the primary accounts that I think best contribute to “…aggressive forest management to ensure effective fire management.” In 2019, $2.1 billion [includes the Forest Service indirect role in the stewardship of nonfederal forests] is available; about the same amount as 2018. The 2020 proposed budget for the same forest management accounts is about $2 billion or a proposed reduction of about $100 million [the actual reduction with the accounts I used is -$90,582,000]. For fire, the 2019 budget is about $3 billion. The 2020 proposal is [up to] $4.6 billion [including the full “fire fix” that is supposed to begin in 2020]. That equates to a possible increase for fire of about $1.6 billion [again, assuming the full “fire fix” funding is used].

        So, the priorities for the 2020 President’s Proposed Budget say, “…reduce forest management and increase fire suppression.” THIS IS EXACTLY OPPOSITE OF WHAT IS NEEDED. The message that “aggressive forest management will ensure effective fire management” is clearly not getting through.

        Again, notice the magnitude of the possible increase fir fire – up to $1.6 billion. I can only imagine the tremendous positive results on the land if there could be the following priority: maintain fire at the 2019 level and increase forest management by +$1.6 billion. I am sticking with my earlier stated required funding level of +$2.2 billion for at least 5-7 years, but a +$1.6 billion increase for forest management actions would be a tremendous beginning. At least this would stay within what Congress has already committed to in terms of their bottom-line Appropriations level. I have not evaluated the most recent budget deal negotiated by Congress. My guess: a continuation of flat budget levels for forest management.

        Clearly, everything is about priorities. And, it has become clear to me that the management of America’s forests is not a real priority for this Administration [in spite of what the President says] and our current Congress — which suggests it is not a priority to us, the American people. And, that’s a shame.

        Part of the reason there is not a top priority for forest management, is there is not a cohesive story that a wide-range of interests can gravitate toward and understand. Forest industry says one thing and scientists say another. Citizenry [people like you and me] say something else. And, government agencies [for example, the Forest Service] are content to conclude another direction. If I say, for example, we need +$2.2 billion per year for the Forest Service for the next 5-7 years, the USDA will say the Forest Service already has too much money.

        Great leaders have the ability to shape a clear vision and the will to advance that vision. What’s missing now are leaders within the Administration and Congress that should have the ability and willingness to state, “…the lack of forest management in America is the natural resource conservation issue of our time. People’s lives, their property and their communities are being wiped away by catastrophic wildfires. It does not have to be this way. We must do something about this. Now is the time.”

        That’s the required first step. Conclude that the lack of forest management is a significant problem. Get the facts lined up. Shape a vision. Then, advance the vision. Pretty basic stuff. But, when things are not a priority, they get succumbed by rhetoric or simply shoved aside. Words become a catchphrase. That is what’s happening now with forest management across our country. And, the 2019 fire season will probably be worse than 2018, which was worse than 2017…and so it goes. Nothing changes.”

        So, what to do? Somehow, someway, we need a “Call to Action” that reaches out to our citizenry to address this national crisis. See my specific response below to this “Call to Action.”

  2. We need a “Call to Action” to address this national crisis, including:
    a. An unprecedented national federal, state and local commitment to aggressively manage America’s forests along the complex rural to urban land gradient.
    b. A Commission to lead the way.
    c. Additional funding.
    d. A long-term commitment [minimum 10 years].
    e. The campaign should be given a brand: For example, “Trees Control Fires, Help Them Succeed.” The following are the suggested steps:

    1) Recognize this [lack of forest management contributing to wildfire that destroy everything in its path] is a national crisis and calls for the formation of a Commission-type group to gather facts; describe the story; and deploy solutions. A Driving Question of the Commission should be: “…how do we stop the current level of destruction caused by large, high intensity wildfires across America’s rural to urban landscapes?”

    2) The Commission shall craft a “Statement of Intent.” For example, “…Moving forward, America’s land management agencies will become much more promotional in the way they carry out their conservation missions. Members of this Commission will be more aggressive in actions and seek opportunities to make new progress to improve the land it is dedicated to care for and the lives of the people it serves. It is largely accepted that the lack of forest management across the country has greatly contributed to the current wildfire situation and the associated impacts on people’s lives and their communities. This is going to change. The work of this Commission will be the beginning of a long-term campaign to ensure our forests become more resilient to disturbances. We will be counting on aggressive, promotional leaders to ensure the direct and indirect roles in the stewardship of America’s forests is achieved, now and ahead. We will be relentless in leading the way.”

    3) Tell the story and shape a vision for change.

    4) Outline new resource requirements for the Trees Control Fires, Help Them Succeed campaign. For example, the Forest Service alone will require an additional $2.2 billion annually for at least 5-7 years with the following distribution [the Commission shall confirm this amount and distribution]:

     +$97 million for “federally assisted state programs [the Forest Stewardship Program] to address the “…strengthening the stewardship of private lands”, as stated by USDA Secretary Perdue.
     +$600 million for hazardous fuels reduction [this brings the overall level for the Forest Service to $1.05 billion]. Not the $4.3 billion per year called for by the General Accounting Office [GAO] in 2013, but an important increase none-the-less over the completely inadequate $450 million being proposed in the 2020 budget.
     +$26 million for fire science and technology development [including defensible space protection in the Wildland Urban Interface].
     +$45 million for the cooperative fire programs.
     +$14 million for forest health protection [specifically, invasive species control].
     +$1.385 billion for management actions on the National Forests.
     +$33 million for biomass uses that include wood-based nanotechnology [cellulose nanomaterials], specifically addressing low value wood, such as hazardous fuel.

    5) Deploy the campaign. This will require a cohesive 10-year plan shaped by the Commission.

    6) Monitoring, evaluation and adjustment [s] of the cohesive 10-year plan.

  3. here are words that are never spoken that would be a bigger help than anything– logging. sawmills. My dear father worked in the woods & sawmills his entire life. when the mills slowly vanished the trees kept on growing. Dad said 40 years ago that when the logging & sawmills were history the forests would burn up. He was right.

  4. Yes. In another key point on my list, I say, “includes timber harvesting, thinning, pruning and prescribed fire are fundamental to the management of trees, forests and forest ecosystems.” Increasing the level of timber harvesting [i.e., logging] is fundamental to the suggest of “aggressive forest management to ensure effective fire management.” As a starting point, this needs to be 6.0 BBF [about twice the current level].

  5. Dave:

    I thought I replied to your message, but for some reason it did not show up. Let me try again:

    In my list of key points regarding “Forest and Fire management: A Call to Action”, point 7 includes “timber harvesting, thinning, pruning and prescribed fire are fundamental to the management of trees, forests and forest ecosystems.”

    You are right. Timber harvesting [i.e. “logging”] is a fundamental piece of “aggressive forest management to ensure effective fire management.” In fact, timber harvesting from the National Forests should be minimally 6.0 BBF — about twice the current level.

    Your Dad was right. Forests are getting clogged up. Forest management — including sustainable logging and innovative biomass uses [i.e., production of cellulose nanomaterials as additives to cement and advanced wood products] — represent a key to helping America’s forests become more resilient to disturbances. Eventually, wildfires will become less intense and can even be used as a landscape conservation tool.

    First, we have to restore the gap created by decades of shifting resources away from management actions to suppress fires. What a paradox! The very activities that help fires become smaller and less intense are eliminated in order to fight fires that have become larger and more intense.

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