Why ‘mega wildfires’ are happening in November

By most accounts, the “Camp Fire” has essentially wiped Paradise off the map. Four days after being forced to flee the blaze, residents are returning home to the Northern California town of 27,000, where 42 people have been confirmed dead and 96 percent of homes and businesses were turned to ash by the deadliest and most destructive fire in California history.

Another two people have been killed by raging wildfires in Southern California, where the Woolsey Fire grew to 35,000 acres in the 24 hours after it started Thursday afternoon. Since then, it has nearly tripled in size. The Camp Fire grew even faster, reaching 70,000 acres in its first day before swelling to 113,000 acres over the weekend.

These two “megafires” — the term for when a wildfire spreads across 100,000 acres — took many by surprise because they struck in November, which is typically a cooling off period for California’s wildfire season. By now, the state should be facing the arrival of its annual rains, but this first flush never came, leaving the land parched and primed for fires.

Drought was not the sole cause of these megafires.

It was a combination of a climate thrown into tumult — dry years mixed with rainy ones — and fires releasing more heat when they burn because of scorched vegetation. That’s the key difference to why wildfires have ravaged the American West in the last two years. These landscapes do not feature overgrown trees, as President Donald Trump suggested over the weekend, but a diverse and fire-loving field of grasses, shrubs and chaparral.

Here’s what everyone needs to know about why these fires are spreading so quickly so late in the year, and how to protect your homes and businesses from them.

Why wildfires are burning so late in the year

Firefighters battle the Woolsey Fire as it continues to burn in Malibu, California, U.S., November 11, 2018. Photo by REUTERS/Eric Thayer

The chain of record wildfires over last two years may give the impression that America is facing a wildfire epidemic. It isn’t.

As Maggie Koerth-Baker reported in July for FiveThirtyEight, the number of individual wildfires has decreased slightly since 1985. The current problem isn’t the number of wildfires but the size of them, which have more than quadrupled over the same time period.

“We’re actually at an all-time low for number of fires,” Crystal Kolden, a pyrogeographer at the University of Idaho, told the PBS NewsHour, but very large fires — megafires — are increasing in frequency.

These giant blazes are a product of wildfires moving swiftly through arid fields and woods. Fire containment is a nightmare under these conditions, because firefighters can’t make any headway against flames that spread so quickly. Such was the case with Camp Fire, where firefighters were forced to spend their early hours on evacuating people rather than containing the rapidly growing fire.

Once upon a time, wildfires burned through vegetation like a pattern on a quilt.

“It’s a heterogeneous pattern that we call a mosaic,” Kolden said. “Some areas are a little bit drier, and fires will burn hotter there. Some areas are a little bit wetter; fires won’t burn as hot there.

When a fire hits a wetter pocket of vegetation, its intensity drops. Instead of 10-foot-tall flames, which can catch tree branches on fire, the wildfire would resemble a feeble camp fire, with flames of about 2 feet.

Climate change has begun restitching this quilt into one large blanket of dry vegetation. In Northern California, a low-water mixture of grasses, shrubs, deciduous trees and conifers — such as the land surrounding Paradise — fuels wildfires.

Firefighters and prison crews walk among chaparral and battle the Woolsey fire in West Hills, Southern California, U.S. November 11, 2018. Photo by REUTERS/Mario Anzuoni

Down south, the flames feed off chaparral, a landscape dominated by bushes called sage scrub. In both places and across the American West, dry weather is extending later into the year, creating a woody tinderbox.

However, these fields were made plentiful by a deluge of rain that swept through California in late 2017 and earlier this year.

“When you have a wet winter, then your biomass tends to grow more. You get a little bit more fuel,” said Nicholas Nauslar, a fire weather forecaster with NOAA’s Storm Prediction Center. Nauslar said when a wet start of the year is followed by a drought, it creates a perfect cycle for wildfires. The vegetation explodes in wet months, only to become fuel during the subsequent droughts.

This see-saw of wet and dry is part of why California has experienced a slate of fast-growing fires two years in a row.

The other factor is wind. In June, Nauslar and his colleagues reported that California’s most destructive fires of 2017 — the North Bay Fires and the Thomas Fire — had grown because of an onslaught of fast-moving winds.

The area where the Santa Rosa fire occurred “had some of the strongest downslope winds in the last 25 years,” Nauslar said. These strong, downslope winds are not due to climate change. They’re a natural feature of the region’s climate, and in Southern California, they carry the romantic name of the Santa Ana winds.

Pushing around heat, these winds help breed wildfire.

Why fires with more heat are so devastating

Fires typically move uphill because flames grow upward, but strong winds can force heat and fires into valleys and across plains. These winds heat up the already dry land, making it more likely to combust.

To learn why this heat is so dangerous, PBS NewsHour visited the National Fire Research Laboratory in Gaithersburg, Maryland. This 32,000-square-foot facility is one of the largest labs in the world dedicated to studying how buildings respond to fire. As part of the National Institute of Standards and Technology, or NIST, their experiments form the basis of fire codes for buildings, furniture and communities.

Inside this massive lab, scientists and engineers set fire to everything from commuter buses to full-sized apartments to determine how they will react, using high-speed cameras to film a panorama for each experiment. This footage becomes the foundation for vivid 3D computer simulations. These simulations can predict how quickly furniture, buildings and wildfire will ignite during outdoor or indoor fires.

Engineers at the National Fire Research Laboratory build full-scale replicas of houses and apartments (pictured), just so they can light them on fire. This experiment led to new fire codes for apartments made of cross laminated timber — a popular building material that easily catches on fire. Image by NIST

Say you wanted to know how a chair in your living room would behave if it caught fire. Your computer model would start by splitting the chair and the space around it into a million small boxes called grid cells, said Kevin McGrattan, a mathematician at the National Fire Research Lab.

“In each of those little boxes, we solve conservation equations of mass, momentum and energy. Any high school student will recognize these basic ideas,” McGrattan said. They rerun these calculations during every second of the video — over and over again — to model how the fire progresses over time. These numbers are combined with measurements of the gases put off by the burning chair, such as oxygen, water vapor or hazardous substances like carbon monoxide. This allows the scientists to explore how the fire brews chemical reactions deep within the material.

But regardless of whether they’re studying a recliner or wreckage from the World Trade Center, one rule reigns supreme — even over temperature.

“For us, the key parameter in these experiments is the heat release rate,” McGrattan said. “That is how much energy is given off by the fire.”

At the National Fire Research Laboratory, scientists predict how blazes will spread inside buildings by burning furniture and other indoor items down to ash. Image by Jaywon Choe

To comprehend the difference between temperature versus the heat release rate, picture this. Let’s say you and your roommate are taking baths in separate bathrooms in your apartment. To set the mood, you have one candle lit, but your roommate splurged and is using 10 candles. All of those candles are burning at the same temperature, but your roommate’s bathroom would feel warmer, because overall, those 10 candles are releasing more heat over the same amount of time. That is, they have a higher heat release rate.

“If you want to simulate a fire in that building, you want to know the heat release rate of all the items that are going to burn in the building,” McGrattan said.

That’s because much like the food that you eat, the things that fuel fires — chairs, walls, grass, shrubs — has calories. When you — or a fire — burns these calories, it generates energy and ups the heat release rate.

At first, the heat from an indoor fire rises and spreads across the ceiling, but eventually that hot layer starts to descend as more heat and smoke is pumped up from the fire, he said. And all of the contents in the room — other chairs, the carpet, any items that are around — start heating up.

Eventually you get what’s called a flashover — when all the items in the room seem to catch fire simultaneously, without the flames actually touching them. Flashovers can occur outdoors, too. Research shows once a fire gets within 33 feet of a home, the fire’s heat can cause combustion.

How to protect your home from indoor and outdoor fires

To help communities fight wildfires, the National Fire Laboratory and NIST works with people like Pam Leschak, the U.S. Forest Service’s national program manager for wildland-urban interface and fire-adapted communities.

Wildland-urban interface refers to places — such as Paradise, California — where human communities bump into unoccupied, untamed land. Housing development in such areas has boomed in the United States, growing from 31 million houses to 43 million houses from 1990 to 2010 — an increase of 41 percent.

One of the most challenging aspects of protecting homes from fires is if they’re located too close together, Leschak said: “Anything closer than about 20 feet, even in a city location, and it’s pretty hard to keep a fire from spreading.” Moreover, many burned forests in the American West are being replaced by fire-prone shrubs and grasses, which grow back faster than trees. The Camp Fire started in an area just outside Paradise where a major fire occurred in 2008, and the vegetation had already grown back thick enough to cause another wildfire.

To stymie the spread of fires to populated environments, Leschak recommends the use of defensible space programs, which involve creating buffer zones around a home, business or community where flammable material is removed.

A number of these programs exist, some built for specific regions like California, but each program involves two buffers zones. The first zone is about 30 feet around your home, including your house itself. In this zone, you’ll want to do following:

• Remove any flammable materials, including propane tanks, lawnmowers, downed trees, limbs, brush and pine needles.
• Keep your lawn watered.
• Store outdoor furniture away when it isn’t being used.
• Swap wooden fences for those made from metal.
• Replace asphalt shingles and wooden roofs with fire-resistant metal, slate or tile.
• Box in any eaves and underspaces.
• Block any crevices around the garage door.

“Windblown embers can get into your garage, and there are usually a lot of things in your garage that can burn,” Leschak said. Strong winds can carry embers for more than a mile.

In the second zone, which extends 30 to 100 feet out from your house, you want to keep your lawn mowed to a maximum height of 4 inches, thin your trees and remove brush. If you live on steep terrain, the zone needs to be wider than 100 feet because flames enjoy moving uphill.

Multiples studies show that defensible space can save a community. An aerial study of San Diego County from 2001 to 2010 found homes that used defensible space were half as likely to burn during a fire.

Kolden has witnessed even stronger protection in a report released in October about Montecito, a town that mostly survived last year’s Thomas Fire, the second largest fire in California history.

Montecito had done a fantastic job of reducing fuel vegetation around all of the houses that were right up against the wildland areas, she said.

“The Thomas Fire made a run at that community last December with the same type of really strong, dry winds that we’re seeing right now with the Woolsey and Camp Fires, and yet Montecito only lost seven homes,” Kolden said. If they hadn’t taken those precautions, Kolden said, Montecito could have lost 400 to 500 homes under a worst-case scenario like the Thomas Fire.

But defensible space only works if whole communities buy into the idea. Much like herd immunity and vaccines, the group can help save individuals. The space shouldn’t only be engineered around homes, but also highways, which serve as escape routes during a wildfire. Wildfire fatalities often occur during evacuation, Kolden said.

“One of the things that we talk about with communities is they need to work really hard on making sure that they are made evacuation routes are brushed back,” Kolden said. “Defensible space is also a safe space for firefighters to work. That’s a really key component that allows it to be successful in protecting homes and protecting lives.”