Researchers find that nearly half of lightning down strikes in California occur with little or no rain

Researchers studied the climatology of dry lightning in California

Dry Lightning, California
(B) Total number of dry lightning flashes across three elevation zones (<1000 m, 1000–2000 m, >2000 m) within the domain for each month between 1987–2020. Text indicates the area of each elevation zone, and inset map shows the geographic distribution of the elevation zones and major mountain ranges. (D) The three elevation zones for each month (bars). Dashed lines in (D) indicate the dry lightning fraction averaged across all months for each zone. Blue dashes in (D) represent the dry lightning fraction computed from all months and elevation zones. (From the paper)

A group of six researchers who studied the occurrence and characteristics of cloud to ground lightning in Central and Northern California found that nearly half, 46 percent, was dry, accompanied by less than 0.1 inch of precipitation.

Of course dry lightning is the bane of land managers and is much more likely to ignite a wildfire than a wet thunderstorm. And on the occasions when there are thousands of down strikes, it can overwhelm the capacity to suppress what can be hundreds of fires.

The six scientists used daily gridded lightning and precipitation observations (1987–2020) in combination with atmospheric reanalyses, to characterize the climatology of dry lightning and the associated meteorological conditions during the warm season (May–October) when wildfire risk is highest.

The paper the group produced is available as open source: “Meteorological and geographical factors associated with dry lightning in central and northern California.”

Daniel Swain, a prolific user of Twitter, used the platform today to highlight some of the group’s findings. In the tweet below, click on “read reply” to see more discussion and illustrations.

The six researchers who participated in the project were Dmitri A. Kalashnikov, John T. Abatzoglou, Nicholas J. Nauslar, Daniel L. Swain, Danielle Touma, and Deepti Singh.

Western wildfire smoke plumes are getting taller

Larger plumes send more smoke higher into the atmosphere where it can spread farther

Pyrocumulonimbus cloud Bootleg Fire Oregon
Pyrocumulonimbus cloud over the Bootleg Fire in Oregon, July 14, 2021. InciWeb.

By Paul Gabrielsen
Science writer, University of Utah

In recent years, the plumes of smoke crawling upward from Western wildfires have trended taller, with more smoke and aerosols lofted up where they can spread farther and impact air quality over a wider area. The likely cause is climate change, with decreased precipitation and increased aridity in the Western U.S. that intensifies wildfire activity.

“Should these trends persist into the future,” says Kai Wilmot, a postdoctoral researcher in the Department of Atmospheric Sciences at the University of Utah, “it would suggest that enhanced Western U.S. wildfire activity will likely correspond to increasingly frequent degradation of air quality at local to continental scales.”

The study is published in Scientific Reports and supported by the iNterdisciplinary EXchange for Utah Science, or NEXUS, at the University of Utah.

Smoke height

To assess trends in smoke plume height, Wilmot and University of Utah colleagues Derek Mallia, Gannet Haller and John Lin modeled plume activity for around 4.6 million smoke plumes within the Western U.S. and Canada between 2003 and 2020. Dividing the plume data according to EPA ecoregions (areas where ecosystems are similar, like the Great Basin, Colorado Plateau, and Wasatch and Uinta Mountains in Utah) the researchers looked for trends in the maximum smoke plume height measured during August and September in each region in each year.

In the Sierra Nevada ecoregion of California, the team found that the maximum plume height increased, on average, by 750 ft (230 m) per year. In four regions, maximum plume heights increased by an average of 320 ft (100 m) per year.

Why? Wilmot says that plume heights are a complex interaction between atmospheric conditions, fire size and the heat released by the fire.

“Given climate-driven trends towards increasing atmospheric aridity, declining snowpack, hotter temperatures, etc., we’re seeing larger and more intense wildfires throughout the Western U.S.,” he says. “And so this is giving us larger burn areas and more intense fires.”

The researchers also employed a smoke plume simulation model to estimate the mass of the plumes and approximate the trends in the amount of aerosols being thrown into the atmosphere by wildfires . . . which are also increasing.

The smoke simulation model also estimated the occurrence of pyrocumulonimbus clouds—a phenomenon where smoke plumes start creating thunderstorms and their own weather systems. Between 2017 and 2020, six ecoregions experienced their first known pyrocumulonimbus clouds and the trend suggests increasingly frequent pyrocumulonimbus activity on the Colorado Plateau.

Taller plumes send more smoke up into higher elevations where it can spread farther, says John Lin, professor of atmospheric sciences.

“When smoke is lofted to higher altitudes, it has the potential to be transported over longer distances, degrading air quality over a wider region,” he says. “So wildfire smoke can go from a more localized issue to a regional to even continental problem.”

Are the trends accelerating?

Some of the most extreme fire seasons have occurred in recent years. So does that mean that the pace of the worsening fire trend is accelerating? It’s too early to tell, Wilmot says. Additional years of data will be needed to tell if something significant has changed.

“Many of the most extreme data points fall within the years 2017 -2020, with some of the 2020 values absolutely towering over the rest of the time series,” he says. “Further, given what we know of the 2021 fire season, it appears likely that analysis of 2021 data would further support this finding.”

In Utah’s Wasatch and Uinta Mountains ecoregion, trends of plume height and aerosol amounts are rising but the trends are not as strong as those in Colorado or California. Smoke from neighboring states, however, often spills into Utah’s mountain basins.

“In terms of the plume trends themselves, it does not appear that Utah is the epicenter of this issue,” Wilmot says. “However, given our position as generally downwind of California, trends in plume top heights and wildfire emissions in California suggest a growing risk to Utah air quality as a result of wildfire activity in the West.”

Wilmot says that while there are some things that people can do to help the situation, like preventing human-caused wildfires, climate change is a much bigger and stronger force driving the trends of less precipitation, higher aridity and riper fire conditions across the West.

“The reality is that some of these [climate change] impacts are already baked in, even if we cut emissions right now,” Wilmot adds. “It seems like largely we’re along for the ride at the moment.”

Scientists hope data collected at prescribed fire will help develop better technologies to detect and monitor fires

Sage multichannel sensing during prescribed fire
Argonne scientists monitor a controlled burn on the Konza prairie in Kansas using the Sage monitoring system. (Image by Rajesh Sankaran/Argonne National Laboratory.)

Scientists recently deployed a complex array of sensors during a prescribed fire at the Konza tallgrass prairie in Kansas to collect a vast trove of data. It was immediately processed at the site using advanced computing technologies provided by a new platform called Sage.

Sage offers a one-of-a-kind combination that involves multiple types of sensors with computing ​at the edge”, as well as embedded machine learning algorithms that enable scientists to process the enormous amounts of data generated in the field without having to transfer it all back to the laboratory. Computing ​at the edge” means that data is processed where it is collected, in the field, while machine learning algorithms are computer programs that train themselves how to recognize patterns.

Sage is funded by the National Science Foundation and developed by the Northwestern-Argonne Institute for Science and Engineering (NAISE), a partnership between Northwestern University and the U.S. Department of Energy’s Argonne National Laboratory.

Equipment used to monitor a controlled burn on the Konza prairie in Kansas using the Sage monitoring system. (Image by Rajesh Sankaran/Argonne National Laboratory.)

The advanced cyberinfrastructure deployed in Sage, which allows for on-the-spot detection, monitoring, and analysis of the burned area, could offer scientists and natural resources officials the ability to get ahead of forest fires with quickly analyzed, multi-instrumented data.

When it comes to forest fires, time is absolutely of the essence,” said Argonne computational scientist and NAISE Fellow Rajesh (Raj) Sankaran. ​Often, there’s no time to move data from the field — where high-speed connectivity might be an issue — to the lab. With Sage, we’re getting the pertinent information we need when we need it.”

The prescribed fire in the Konza prairie gave the researchers a large collection of data — almost 60 DVDs worth — full of information about the progression of smoke and fire. This data can be used to educate a machine learning algorithm that can make further determinations of the behavior of other fires in real time.

After the success of the Sage network in Kansas, future plans exist for the network to be deployed in California, Colorado, Illinois, and Texas as part of a network led by the National Ecological Observatory Network (NEON). Eventually, researchers hope to establish a continent-spanning network of smart sensors that could employ Sage technology. ​

NEON is developing a mobile deployment platform that can complement land-based and aquatic sites all over the country,” Sankaran said. ​Sage can play a supportive role in many different environments throughout the United States.”

Firefighting classified as carcinogenic to humans

We asked scientists how the findings apply to wildland firefighters

crew from Minnesota
A crew from Minnesota mopping up on the King Fire east of Placerville, California in 2014. Incident Management Team photo.

The International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organization (WHO), has evaluated the carcinogenicity of occupational exposure as a firefighter.

A Working Group of 25 international experts, including 3 Invited Specialists from 8 countries was convened by the IARC Monographs program for a meeting in Lyon, France.

After thoroughly reviewing the available scientific literature, sufficient evidence led the Working Group to classify occupational exposure as a firefighter as carcinogenic to humans.

A summary of the final evaluations has now been published. The detailed assessment will be published in The Lancet Oncology in 2023 as Volume 132 of the IARC Monographs.

Evidence for cancer in humans 
The study found that occupational exposure as a firefighter causes cancer. There was sufficient evidence for cancer in humans for mesothelioma and bladder cancer.

There was limited evidence for cancer in humans for the following cancer types: colon cancer, prostate cancer, testicular cancer, melanoma of the skin, and non-Hodgkin lymphoma.

Strong mechanistic evidence 
The evaluation of the mechanistic evidence was based on exposures associated with fighting structure and wildland fires. There was strong mechanistic evidence in exposed humans that occupational exposure as a firefighter exhibits 5 of the 10 key characteristics of carcinogens: “is genotoxic”, “induces epigenetic alterations”, “induces oxidative stress”, “induces chronic inflammation”, and “modulates receptor-mediated effects”.

Exposure of firefighters
Firefighters are exposed to a complex mixture of combustion products from fires (e.g. polycyclic aromatic hydrocarbons, volatile organic compounds, metals, and particulates), diesel exhaust, building materials (e.g. asbestos), and other hazards (e.g. heat stress, shift work, and ultraviolet and other radiation). In addition, the use of flame retardants in textiles and of persistent organic pollutants (e.g. per- and polyfluorinated substances) in firefighting foams has increased over time.

This mixture may include many agents already classified by the IARC Monographs program in Group 1 (carcinogenic to humans), Group 2A (probably carcinogenic to humans), and Group 2B (possibly carcinogenic to humans). Dermal exposure, inhalation, and ingestion are common routes of exposure, and biomarker studies among firefighters have found enhanced levels of markers of exposure to polycyclic aromatic hydrocarbons, flame retardants, and persistent organic pollutants.

Most studies of firefighter health evaluate structural firefighters. We asked Dr. Kenny Fent and Dr. Kathleen Navarro of the National Institute for Occupational Safety and Health (NIOSH) questions about how these findings apply to wildland firefighters. Here is their joint response:

Summary of IARC Evaluation for Wildland Firefighters
The IARC evaluation of Occupational Exposure as a Firefighter included a review of the available scientific literature on occupational exposures, cancer epidemiology and the key characteristics of carcinogens. The evaluation did not differentiate between structural and wildland firefighters in making the determination of carcinogenicity. This is because the working group was not able to differentiate structure fire exposures (and other exposures) from wildfire exposures for firefighters in at least some of the cancer cohort studies that were included the evaluation.

In addition, many of the studies that provided the evidence of carcinogenicity included the evaluation of the key characteristics of carcinogens (intermediate health outcomes on the pathway to cancer). These included studies of wildland firefighters working on wildfires and prescribed fires.

Lastly, the exposure studies reviewed supported that both structural and wildland firefighters were exposed to similar types of carcinogens. As a result, the definition of “occupational exposure as a firefighter” for the IARC evaluation was kept broad and included a variety of hazards resulting from fires (e.g., structure, wildland, and vehicle fires) and other events (e.g., vehicle accidents, medical incidents, hazardous material releases, and building collapses).

Is mesothelioma only caused by exposure to asbestos, and are wildland firefighters generally exposed to it?
Yes, mesothelioma is caused by exposure to asbestos. Asbestos exposure is generally rare among wildland firefighters, with the exception for wildland firefighters who commonly encounter built environments (especially buildings constructed before the 1970s), areas with contamination (e.g., Libby, MT) or naturally occurring asbestos. A past NIOSH Health Hazard Evaluation reported that exposure to total asbestos fibers in air were less than the lowest occupational exposure limits while conducting a prescribed burn. However, the highest concentrations measured were during tasks with greater plant and soil disturbance and where water was not used (e.g., fire line construction and dry mop-up).

Dr. Kenny Fent leads the National Firefighter Registry at NIOSH and was the chair of the exposure characterization subgroup for the IARC working group.

Dr. Kathleen Navarro leads the Wildland Firefighter Safety and Health program at NIOSH and was a Representative of a national health agency for the IARC evaluation.

Respirator being developed for wildland firefighters

Wildland fire respirator
Development of a wildland fire respirator. Two versions are being tested, with the filter being carried on the chest hip. Department of Homeland Security photo.

A working group for the International Agency for Research on Cancer, the cancer agency of the World Health Organization, has just “classified occupational exposure as a firefighter as carcinogenic to humans.” Part of the reason is the toxic gasses firefighters are exposed to.

Wildland firefighters working on a vegetation fire can’t wear the conventional self contained breathing apparatus used by structural firefighters. It is too bulky, heavy, and only lasts 10 to 30 minutes.

In an effort to provide less carcinogenic air to wildland firefighters, the Department of Homeland Security’s Science and Technology Directorate  is developing a respirator capable of removing airborne hazards present in the wildland firefighting operating environment. They are working with the International Association of Firefighters, National Fire Protection Association, International Association of Fire Chiefs, U.S. Forest Service, and local Colorado fire departments to develop and test the Directorate’s Wildland Firefighter Respirator (WFR). It contains a HEPA filter module that will remove very fine particulates, and a carbon sorbent to remove toxic gases. The team is investigating wildland firefighter-approved designs like the Radio Carrier and Hip-Mounted units shown in the photo below.

Wildland fire respirator
Development of a wildland fire respirator. Two versions are being tested, with the filter being carried on the chest hip. Department of Homeland Security photo.

The WFR was designed around a lightweight mask covering just the mouth and nose. It relies on filtration, designed to go a whole shift before needing to be changed.

“Our system pushes clean air to firefighters using a powered blower with HEPA and carbon filters,” said S&T Program Manager Kimberli Jones-Holt. The system connects to the half-mask through a lightweight, flexible breathing hose to provide clean air and draws in air from the bottom of the unit to prevent rain or water infiltration.

“The filters were also designed to be inexpensive and easily replaced at $5 to $10 each,” Jones-Holt continued.

It uses an electric blower to force filtered air to the mask, relying on AA batteries for power.

The DHS says if wildland firefighters use respiratory protection, their careers could be significantly extended, leading to a more educated and experienced workforce capable of more efficient operations, with lower medical bills and training costs.

Thanks and a tip of the hat go out to Bob.

Study confirms extreme wildfires of 2020 in Western Oregon were not unprecedented

satellite photo fires smoke Washington, Oregon, and California
GOES-17 photo of smoke from wildfires in Washington, Oregon, and California at 5:56 p.m. PDT Sept. 8, 2020. The photo was taken during a very strong wind event.

By U.S. Forest Service

When the 2020 Labor Day Fires torched more than 300,000 hectares over the span of two weeks in parts of western Oregon and Washington, they devastated communities and put the threat of west-side fires squarely into focus. A new study led by the USDA Forest Service’s Pacific Northwest Research Station examines the context surrounding the fires and offers insight into the historical role of large, high-severity fires—and the future of wildfires—west of the Cascades.

“Without a doubt, the 2020 Labor Day Fires were a significant fire event on many levels, and one that was a wake-up call for the region,” said Matthew Reilly, research forester and lead author of the study, which is published in the journal Ecosphere. “The goal of our study was to help understand how this event compared to past west-side fires so that we can help inform adaptation strategies aimed at preventing or mitigating similar events in the future.”

Drawing from a literature review, extensive historical data, and new analysis, Reilly and his co-authors explored five questions surrounding the 2020 Labor Day Fires: how the 2020 fires compared with historical fires in the region, the role of weather and climate, the effects of forest management and pre-fire forest structure on burn severity, the impacts of these fires on west-side landscapes, and what can be done to adapt to similar fires in the future. Ultimately, they found that the 2020 fires were remarkably consistent with historical fires on the west side, both in terms of their timing and size and the cause of their rapid spread—dry conditions combined with strong east winds.

“Our findings suggest that these severe fires are normal for west-side landscapes when you look at historical fire regimes at longer time scales,” Reilly said. In fact, the researchers identified similarly large historical fires in the early 20th century under similar weather conditions—some even burning right around Labor Day—in some of the same locations that burned in 2020.

Because of the abundant and productive forests characteristic of the west side and the driving role of extreme winds, conventional fire management tools used in dry forests, like prescribed burning and fuels management, will likely be less effective in west-side forests than they are on the east side. This is particularly the case, their study found, when fire weather conditions are as extreme as those witnessed during the 2020 fires.

“Our study indicates we need very different approaches and adaptation strategies in west-side forests compared to those we use in dry forests,” Reilly said.

The study was conducted as part of the Pacific Northwest Research Station’s ongoing West-side Fire Research Initiative, which was launched in 2019 to develop science-based tools to help resource managers respond to wildfire risk in west-side forests. The study’s coauthors are from the Washington State Department of Natural Resources, University of Washington, Oregon State University, and USDA Forest Service’s Pacific Northwest Region.


  • The 2020 Labor Day Fires were much larger and more severe than others in the recent record, but they were remarkably consistent with many historical fires. Strong east winds and dry conditions are the common denominators in both large historical fires of the past and the 2020 fires.
  • Forest management and fuel treatments are unlikely to influence fire severity in the most extreme wind-driven fires, like the 2020 Labor Day Fires. Pre-fire forest structure, largely the result of previous forest management activities, had little effect on burn severity when east winds were strong during the 2020 fires.
  • Fuel treatments around homes and infrastructure may still be beneficial under low and moderate fire-weather conditions.
  • Adaptation strategies for similar fires in the future in west-side communities might, instead, focus on ignition prevention, fire suppression, and community preparedness.

More information:

Matthew J. Reilly et al, Cascadia Burning: The historic, but not historically unprecedented, 2020 wildfires in the Pacific Northwest, USA, Ecosphere (2022). DOI: 10.1002/ecs2.4070

Wildfire Today, articles posted in September, 2020 tagged Oregon, or Washington.