According to the National Weather Service, a combination of strong offshore winds and very dry conditions is creating “potentially historic” fire conditions in the northern Bay Area. Meanwhile, “critical to extreme threats are likely to persist” across north-central and southern California further into this week.
There are several factors which contribute to the spread of wildfires, including high wind speeds, low air humidity, warm air temperatures, as well as both live and dead fuel moisture, according to Robert Fovell, a professor in the Department of Atmospheric and Environmental Sciences at the University at Albany.
“The very worst combination of those occur at this time of year,” he told Newsweek. “California has a Mediterranean climate, which means it’s winter wet and summer dry. Fire risk is highest in the autumn, after the long, dry, hot summer but before the winter rains (when those do come.)”
“In Southern California, Santa Ana wind events start in September. Descending air becomes warmer due to compression, and drier because relative humidity decreases very quickly with temperature in those conditions. In wind corridors, the downslope winds can also be very fast. So Santa Ana winds—and in Northern California, Diablo winds—can bring high fire danger, owing to low live fuel moisture, low humidity and high temperature.”
Part of the problem for California currently is that the air above the region is dry for this time of year, according to the NWS. Meanwhile, several parts of the state have not seen rain for several weeks.
“Many of the areas in California being impacted by wildfires have not experienced measurable rainfall since mid-September 2019,” Scott Carpenter, an NWS meteorologist, told Newsweek. “October typically begins the period of the year where more rainfall is expected to fall, heading into the wet season which extends through the winter.”
Couple this dryness the fact there is plentiful vegetation—a result of a wet winter—which has now dried out due to warm air temperatures, providing plentiful fuel, and you have the perfect conditions for fires to spread.
“Live fuel moisture (LFM) reaches a minimum in autumn,” Fovell said. “LFM is currently 61 percent, and values below 75-80 percent are considered a problem.”
In addition to the aforementioned factors, the fire risk is then exacerbated by strong winds blowing inland from the sea, which have affected certain parts of the state in the past few days. For example, powerful gusts affected the North Bay region in particular, including Sonoma County—helping to spread the Kincade fire which has grown rapidly in just a few days to cover of an area of more than 60,000 acres.
“This particular wind event over the weekend in the Bay Area lasted much longer than the wind event in 2017 which was a factor in spreading the North Bay Fires quickly in 2017,” Carpenter said.
And forecasters are predicting that strong winds will continue to affect the state for the next few days. Gusts of between 60 and 70 miles per hour are expected to hit Northern California on Tuesday and Wednesday, while Southern California could experience gusts with speeds of up to 75 miles per hour into Thursday, CBS News reported.
Last year, California experienced the deadliest and most destructive wildfire season in recorded history, which burned a total of nearly two million acres and led to the deaths of more than 100 people.
“In early 2019, the state emerged from a long-term drought, giving some hope that this year would be less intense,” Robin Verble, an Associate Professor of Biological Sciences from Missouri University of Science and Technology, told Newsweek.
“By mid-August, there was a 90 percent decrease in the total acreage burned in the state; however, recent fires may change those statistics considerably. We ultimately won’t know the outcome of the 2019 fire season until it’s over, but the rest of the year is likely to produce higher severity fires as Santa Ana winds increase.”
Many of the factors that drive wildfire risk are influenced by variations in the climate. In fact, experts say that climate change will lead to hotter, drier conditions in many regions, which can increase the risk and severity of wildfires. This is largely due to the fact that warmer and drier conditions provide better conditions for fires to spread, making them harder to extinguish.
“Changing climates are intensifying the effects of fire—models from twenty years ago told us to expect more frequent fires, more intense fires, and more overall acreage burned,” Verble said. “We’re seeing those predictions come true now. In Northern California, longer heat waves and drier summers are resulting in drier fuels and increased wildfire risk. Current models suggest that this wildfire risk is going to intensify into the future.”
In the United States, for example, large wildfires are burning almost double the area they did in the 1970s and, furthermore, the average fire season is lasting about 78 days longer, according to the Center for Climate and Energy Solution.
While wildfires are a natural part of California’s landscape, the fire season in the state and across the West is starting earlier and ending later each year, according to the California Department of Forestry & Fire Protection.
“A little bit of warming is leading to a lot more burning, Jennifer Balch from The University of Colorado-Boulder, told Newsweek. “In the western U.S., regional temperatures have increased by almost two degrees Fahrenheit since the late 1800s, snowmelt is occurring a month earlier in some places, and fire season length has increased by almost three months.”
“Human-caused warming has effectively made fuels much drier and doubled the amount of western forests that have burned since 1984,” she said. “In California, we know there is a direct link between warmer temperatures and more fires, particularly in forests. Since the 1970s, the amount of burned area in California has increased five-fold.”
But the effects of climate change on wildfires are not just about increases in heat and longer dry periods. California is also experiencing more frequent and intense Santa Ana and Diablo winds.
“These are driven by temperature/pressure differentials in our inland desert regions versus our coastal plain,” Sean Anderson, a Professor of Environmental Science & Resource Management from California State University Channel Islands, told Newsweek. “The pressure cells in eastern California or Nevada/Arizona persist for days to weeks on end whereas they used to only persist for hours to days. This drives more and more wind events.”
“Much of the destruction we’ve seen in recent years is from these intense, wind-driven fires,” he said. “This is what happened in the North Bay Fires two years ago, the Thomas Fire two years ago, the Woolsey and Camp fires last year, etcetera.”
It should be noted, however, that while the environment provides the right conditions for fires to spread, people are actually responsible for starting 84 percent of blazes in the United States—whether intentionally or accidentally— according to Balch.
“And it’s not just downed power lines that cause sparks,” she said. “Campfires, burning debris, driving off the side of the road, electrical equipment, and fireworks are just some of the many ways that we start fires.”
Furthermore, as a result of rapid rural development, more than 11 million people in California—at least 25 percent of the state’s population—live in what’s known as the wildland-urban interface (WUI,) according to the MIT Norman B. Leventhal Center for Advanced Urbanism.
The WUI is defined as a “developed area that meets or intermingles with undeveloped wildlands,” and is associated with increased risk of wildfires. This has significant implications for urban planners, according to Verble.
“In Los Angeles, we see a densely populated city, a sprawling suburban landscape, and a fire-dependent dry subtropical plant community,” Verble said. “These things don’t mesh well together. As populations grow, more humans are packed into an ecosystem that will burn. We cannot expect nature to change these things to suit our needs, so it is our job as humans to adapt our patterns of colonization, our structures, our infrastructure, and our communities to prepare for the inevitable.
“The idea of fundamentally retooling our existing national infrastructure and cities to deal with these large environmental issues doesn’t seem to be politically popular, but each year, these same sorts of situations are being faced in different cities and locations across the country, and there has to be a moment where the communities that are impacted demand accountability from their leaders,” Verble said.
The graphic below, provided by Statista, illustrates the growing cost of fighting the wildfires over the years.
This article was updated to include an infographic.
