Why are fires in the West growing larger this year?

Drought — fuel moisture — energy release component

Observed precipitation
Observed precipitation during the 30 days before August 23, 2021.

There are a number of ways to analyze the behavior of wildland fires using data that is easily available. The amount of moisture in the live and dead vegetation is a critical factor in determining how readily it will burn, because it has to be cooked off before the grass, brush, or woody vegetation will vigorously combust.

The amount of precipitation over days, weeks, months, and years affects how wildfires burn. The map above depicts precipitation during the 30-day period ending August 23, 2021.

The Drought Monitor is one way of using an index to express how the precipitation compares to normal for an area. As you can see below most of California is in either Exceptional Drought (the highest level of drought) or Extreme Drought. The only areas in California that are not, are a tiny sliver in the extreme northwest corner, and the five southernmost counties. Both drought categories can also be found in areas of Oregon and Idaho which I will get to later.

Drought Monitor, August 17, 2021

Extended drought lowers the moisture content of both live and dead vegetation. When that occurs, it takes less energy out of a fire to cook off the moisture, and that energy instead goes toward enhanced combustion of the material and then preheating and igniting nearby vegetation, resulting in faster spread of the fire.

The observed precipitation map at the top of the page shows that most of California received less than 1/10 inch in the 30-day period. This, and the multi-year drought has led to the 1,000-hour time-lag fuels, woody material 3 to six inches in diameter, being extremely dry. Fuel monitoring stations in the foothills of the Sacramento Valley and the Northern Sierras are finding moisture levels lower than kiln-dried lumber, which is usually 8 to 12 percent. Both stations recently have been recording levels around 6 percent, which is near and sometimes below the lowest levels ever recorded for the date (the red lines on the charts). The Incident Management Team on the Caldor Fire said the 1,000-hour fuels are at three percent moisture.

1,000 hour fuel moisture Sacramento Valley-Foothills fire

In these charts, “Min” is the historic minimum for the date. “Max” is the historic maximum for the date.

1,000 hour fuel moisture, Northern Sierras

Knowing the moisture content of the fuel is an ingredient in determining another index, the Energy Release Component (ERC) which can help predict the intensity and rate of spread of a fire. It is defined as a number related to the available energy (BTU) per unit area (square foot) within the flaming front at the head of a fire. The ERC is considered a composite fuel moisture index as it reflects the contribution of all live and dead fuels to potential fire intensity. As live fuels cure and dead fuels dry, the ERC will increase and can be described as a build-up index. The ERC has memory. Each daily calculation considers the past 7 days in calculating the new number. Daily variations of the ERC are relatively small as wind is not part of the calculation.

Since mid-May the ERCs at two locations in Northern California have been flirting with the historic daily highs, either slightly above or slightly below. This is consistent with the observed fire activity this year on several large fires in the northern part of the state. The Dixie Fire is closing in on three-quarters of a million acres, and the Caldor Fire in nine days has blackened 117,000 acres. Fire Behavior Analysts at the fires are describing historically low fuel moistures.

Here is an excerpt from the recent Fuel Model Summary for the Caldor Fire:

There is a heavy dead and down component with drought-stressed fuels. Live fuels are cured to levels normally seen in late September, and fuels are extremely receptive to spotting. Fuel moistures are historically low. Northern California remains under a Fuels and Fire Behavior Advisory. ERC’s are above the 97th percentile. 100 hr and 1000hr fuels are below the 3rd percentile.

These fires are primarily fuel-driven. They are burning very well with gentle breezes. When the wind increases above 10 mph, they are hauling ass.

ERC Sac Valley-Foothills fire
Energy Release Component, Northern Sierras fire
Continue reading “Why are fires in the West growing larger this year?”

Award granted to develop system to detect and forecast the spread of all wildland fires in U.S.

Pyregence fire forecasting tool
Pyregence fire forecasting tool, beta version. Forecast for the northeast side of the Red Salmon Complex of fires in Northern California at 4 p.m. PDT October 9, 2020.

The U.S. Department of Commerce’s National Institute of Standards and Technology (NIST) has awarded 19 small businesses in 12 states a total of more than $4.4 million in grants to support innovative technology development. One of those grants, for $100,000, is to help build a system for automatically detecting and forecasting the spread of every wildfire in the continental United States and updating the forecasts as conditions change.

Reax Engineering Inc. of Berkeley, California, the company that received the grant, has a beta version of the forecasting tool online now just for the state of California. It is a work in progress and will eventually include data for fires in other  states.

Wildfire forecasting is one of the four primary goals of Pyregence, a group of fire-science labs and researchers collaborating about wildland fire, where the forecasting tool now resides. The organization brings together initiatives and leading researchers from 18 institutions representing industry, academia, and government in an effort to transform how wildfire mitigation and adaptation measures are implemented. In addition to forecasting wildfire activity, wildfire scenario analyses will be produced to inform future wildfire risk and California’s 5th Climate Change Assessment, using open science and technology principles.

Pyregence working groups
Pyregence working groups.

In order to predict the spread of wildfires, fire behavior models are run on computers. The versions that have been used for decades are not accurate for dealing with heavy dead and down fuels or fires spreading through the crowns of trees under extreme weather conditions. The goal of one of the four Pyregence workgroups, the Fire Behavior Workgroup, is to improve existing models or develop new ones. That effort is being led by Scott Stephens, Professor of Fire Science, and director of the University of California Center for Fire Research and Outreach.

Missoula Fire Lab burn chamber
U.S. Forest Service Missoula Fire Lab burn chamber, May 21, 2014. Photo by Bill Gabbert.

Mark Finney, a researcher at the U.S. Forest Service Missoula Fire Sciences Laboratory, is part of the Fire Behavior Workgroup and will soon have access to a burn chamber much larger than the one in the photo above. It will reportedly be the size of a grain silo. These wind tunnel/combustion chambers are used to conduct burning experiments in a controlled environment under varying fuel, temperature, humidity, and wind conditions. It can lead to a better understanding of how vegetation burns, leading to improvements in predicting fire spread.

An article at Wired describes the planned burn chamber:

Once complete, that chamber will let him replicate wildfire fuel beds by piling logs and other material as much as a few feet deep. He will then ignite them, hit them with wind and moisture, and quantify their burn rate and energy-­release rate—what he calls the “heat-engine part of mass fires.”

“Really what we’re looking for,” Finney says, “is how these things transition to flaming. Instead of just smoldering on the forest floor, how do they become actively involved in these large fires?”

If all goes well, Finney’s working group will eventually code three-dimensional digital simulations of various wildland fuel beds—digital cubes, in essence, not unlike Minecraft voxels—that can be stacked and arranged in infinite variation across landscapes generated by GIS mapping data.

Researchers study factors that affect long-distance spotting of wildfires

The results could lead to more accurate models for spotting and fire behavior

map spot fires wildfire Australia
New South Wales Rural Fire Service line scan showing three separate source fires (three largest polygons). Most actively burning fire is yellow, orange is still hot after main fire front has passed, brown is extinguished, green is unburnt vegetation, blue is part of the smoke plume. Red dotted lines indicate spot fire (small polygons) distances measured for analysis. Red arrow indicates spread direction. (from the research)

Data collected in an Australian study could lead to the development of more accurate predictive models for wildfire behavior and spotting, especially for extreme wildfires.

Burning embers driven ahead of a wildfire can dramatically increase the rate of spread and the danger faced by firefighters and the public. Under moderate burning conditions a small number of spot fires might be suppressed if enough firefighting resources are available, but on large plume-dominated fires pushed by strong winds spot fires far from the  main fire can burn together making suppression at the head of the fire impossible. In many cases ember showers have been the primary ignition source for the destruction of structures in the wildland urban interface.

During the 2009 Black Saturday bushfires in eucalpyt-dominated forests in Australia the maximum spot fire distances were 30 to 35 km (18 to 22 miles) and during the 1965 wildfires in eastern Victoria were 29 km (18 miles). Spot fires in North America have been documented at distances of up to 19 km (12 miles).

A research paper on spotting distance in Victoria and New South Wales was published earlier this week by the International Journal of Wildland Fire, written by Michael A. Storey, Owen F. Price, Jason J. Sharples, and Ross A. Bradstock, titled “Drivers of long-distance spotting during wildfires in south-eastern Australia.”

The researchers took advantage of the increasing use of airborne mapping technologies on wildfires in Australia, including infrared and multispectral line scanning, to analyze data from 338 observations. (See map above.) They used ArcGIS to manually draw polygons and determine the size of the actively burning areas of the fire, which they called “source fire area”, and measured the distance to spot fires and the size of each. They also collected fuels, weather, and topography information.

Below is an excerpt from the research:

Maximum spot fire distances ranged from 5.0 m to 13.9 km (mean, 0.9 km; 95th percentile, 3.9 km). The mean number of spot fires per source fire (irrespective of distance) was 13. The distribution of maximum distance values appeared exponential, with a high proportion of shorter distances (Fig. 4a). Very long-distance spotting was rare; only 11 source fires had a maximum spotting distance >5 km.

maximum spot fire distances
Frequency distribution histograms of (a) maximum spot fire distance values from each source fire and (b) number of long-distance spot fire (>500 m) values from each source fire. (from the research)

Eleven of the fires had spotting distances more than 5 km (3.1 miles). The longest distance measured to a spot fire was 13.9 km (8.6 miles).

The analysis of 338 wildfire line scan observations found the size of the active area of the source fire to be the strongest predictor of long-distance spotting. Important secondary effects were fuel, weather, and topography.

Excerpts:

Wind speed was important to both Maximum-distance and long-distance Spot-number. Upper-level wind speed had weaker but still significant effects in the models. Wind at different levels can influence many aspects of wildfire behaviour, including plume development, plume turbulence and tilt, fire intensity, vorticity development, firebrand transport and ignition likelihood in receiver fuels.

A steep slope somewhere within the source fire (i.e. source fire max. slope) increased the maximum spot fire distance and the probability of spot fire occurrence >500 m. TRI [Terrain Ruggedness Index] performed similarly but was highly correlated with slope (>0.9), so was not included in the same models. An area of relatively high wind exposure (e.g. exposed ridge) also increased maximum spotting distance. Slope and wind exposure may be important through interactions with wind, changing wind speed, increasing turbulence and potentially enhancing pyroconvection, leading to enhanced firebrand generation and transport.

[W]e did not find a commonly used measure of bark spotting potential to be a significant predictor. Our results suggest that to accurately predict long-distance spotting, models must incorporate a measure of source fire area. Gathering data on spotting and plume development at wildfires over a range of intensities (including measuring intensity and frequent line scans) and improving fuel maps should be prioritised to allow for the development of reliable predictive spotting models.

The fibrous or stringy bark on some eucalyptus species is particularly suited aerodynamically for being lofted in a convection column and traveling for long distances while still burning, and is one of the primary ignition sources for long range spotting in Australia. The bark on North American trees is different, but the methods used by the Australian researchers could be used to collect similar spot fire occurrence data in the United States and Canada which could lead to improved spotting and fire behavior models.

Fourth grader needs suggestions for wildfire demonstration

Let’s also come up with ideas for gatherings of adults

demonstration of pyrolysis
Apparatus for demonstration of pyrolysis, used back in the day.

Today I received a message from a mom who needs our help:

Hi-

My son chose the topic of wildfires for his project on natural disasters. We’re having a hard time thinking of a demonstration that’s safe for his classroom. Do you have any suggestions?

Thank you.

So, I’ll put this out there for our readers. Can you help out this fourth grader that has an interest in wildfires? The young man needs to choose a demonstration this week. Leave a comment with your ideas.

The tricky part is coming up with something that will be safe to do in a classroom full of 10-year olds.

The first thing that came into my mind was a demonstration of pyrolysis, the process of combustion of vegetation. Before canned training was developed for entry level wildland firefighters, we wrote lesson plans and stood before the new hires and taught them about fire behavior, line construction, weather, and fire science. At least that’s the way we did it on the El Cariso Hotshots.

One demonstration I used that would not be safe for a fourth grader without adult supervison, was pyrolysis; showing them that when wood or vegetation is consumed in a fire, it’s actually a gas that is burning. It would be best to do this outside in an area cleared of flammable material. Stuff a coffee can with some sawdust or dried vegetation (grass or brush). Take aluminum foil and form it into an upside down funnel and place it around the top of the can, making it as air-tight as possible (similar to the photo above). Then make a hole a little smaller in diameter than a pencil at the top of the foil. Place the can on a heat source, such as a stove, and wait until a steady stream of smoke comes out of the hole at the top. Then hold a long butane lighter used for igniting a BBQ grill adjacent to the smoke and watch the gas burn. A version of this is described on YouTube.

Another demonstration that absolutely would not be suitable for a fourth grader is something we wrote about in 2008:


Everybody at some point has played with matches. Mike Dannenberg of the Bureau of Land Management, a fire suppression supervisor in Montana and the Dakotas, puts on a presentation about residential fire preparedness that involves hundreds of matches. The article at wvmetronews.com has more details as well as a series of photos. Here is an excerpt.

“I liken it to building in a flood plain,” said Dannenberg. “If you thin around your house, if you reduce the fuel load, if you build out of materials that are not combustible a lot of times it will protect your home.”

Demonstration fire slope clearance
Demonstration of fire on a slope, and how a clearance around structures can be effective..

Dannenberg has created a demonstration model to show the intensity of a canopy fire. He loads a pegboard with hundreds of match sticks. Each match represents a highly combustible evergreen tree. A road snakes through the middle of the model forest. The upper corner of the board features a homestead with a house, garage, and various outbuildings. The scene is created to the specs recommended by the BLM. Each building is covered with a metal roof and the yard space has only sparse and wide spaced trees.

Dannenberg tilts the board to replicate the speed of a fire moving up the slope of a hill or mountain. He lights a single match at the far end of the pegboard and at the foot of the simulated hill. The fire spreads rapidly, but stops short of the home–leaving it untouched. It’s an effective demonstration that Dannenberg says plays itself out every summer in the western United States.


UPDATE, February 24, 2020: 

There are some good ideas in the comments. Keep them coming. Like the one above (the matches on the peg board) some of them are not appropriate for fourth-graders, but somebody somewhere might find them useful at another venue. So think about gatherings of adults as well.

Fire whirl, or waterspout, or fire tornado?

Spectacular video at a fire near Blythe, California

Above: screenshot from the video below.

Chris Mackie posted this video on July 15, 2018 of spectacular fire behavior at a wildfire on the Arizona side of the Colorado River near Blythe, California. It is not uncommon to see dust devils and fire whirls during unstable weather conditions on a fire, but as you can see beginning at about 1:10 the rotating vortex over this fire intensifies into what some might call a fire tornado (or “firenado”) as trees are uprooted and debris is thrown into the water as it moves over the river (and transforms into a waterspout?).

We have written about similar phenomenons several times on Wildfire Today. Here is an excerpt from a 2016 article, “Defining fire whirls and fire tornados”:


“The news media sometimes calls any little fire whirl a “fire tornado, or even a “firenado”. We found out today that these and related terms (except for “firenado”) were, if not founded, at least documented and defined in 1978 by a researcher for the National Weather Service in Missoula, David W. Goens. He grouped fire whirls into four classes:

  1. Fire Devils. They are a natural part of fire turbulence with little influence on fire behavior or spread. They are usually on the order of 3 to 33 feet in diameter and have rotational velocities less than 22 MPH.
  2. Fire Whirls. A meld of the fire, topograph, and meteorological factors. These play a significant role in fire spread and hazard to control personnel. The average size of this class is usually 33 to 100 feet, with rotational velocities of 22 to 67 MPH.
  3. Fire Tornadoes. These systems begin to dominate the large scale fire dynamics. They lead to extreme hazard and control problems. In size, they average 100 to 1,000 feet in diameter and have rotational velocities up to 90 MPH.
  4. Fire Storm. Fire behavior is extremely violent. Diameters have been observed to be from 1,000 to 10,000 feet and winds estimated in excess of 110 MPH. This is a rare phenomenon and hopefully one that is so unlikely in the forest environment that it can be disregarded.”

A new app to predict wildland fire behavior

Wildfire Analyst Pocket appTechnosylva has released a new free app for smart phones that can help predict fire behavior. It is called Wildfire Analyst Pocket and is available for Android phones. It will soon be on the Apple app store as well.

In a video filmed May 21, 2018, the president of the company, Joaquin Ramirez, introduces us to the app.

Technosylva is one of the companies that produce systems available now that could lead toward the Holy Grail of Wildland Firefighter Safety, tracking in real time the location of firefighters and a wildfire.