It’s The Wind Stupid

During the 1992 Presidential Election cycle, political advisor James Carvel devised a brief and successful mantra that helped Bill Clinton win the election: “It’s the economy, stupid.”

A similar mantra could characterize all large wildfires in the United States: “It’s the wind, stupid.” Although numerous elements contribute to fire spread, including slope, topography, fuel type, and other factors, wind is the agent that creates unstoppable large high severity blazes.

Four major climate-weather controls support wildfires: drought, low humidity, high temperatures, and wind. But the most important factor is wind. According to at least one paper, wind accounts for over 90% of fire spread.

All large wildfires are driven by wind, not fuel. I do not know of any exceptions.

Extreme fire weather events are responsible for the majority of acreage burned. One paper concludes: “Fire season climate variables were correlated with the annual number of extreme events and area burned.”

Logging does nothing to reduce wind, and can enhance its influence on fire spread.

Wind drives wildfire spread in several ways. It carries away moisture-laden air and hastens the drying of forest fuels. It provides fresh oxygen to the blaze, fans the flames, can preheat fuels, and, perhaps most importantly for the creation of large wildfires, tosses embers well ahead of the fire front, igniting new blazes, making it all but impossible to stop a wind-driven fire.

The wind’s effect is not linear. In other words, increasing wind speed from 10 mph to 20 mph does not double fire spread; instead, it leads to exponential fire growth and increases the burn intensity.

“The amount of reduction in speed and change of direction depends upon the roughness of the earth’s surface. It follows then that the effect of friction is least over smooth water and greatest over mountainous topography.” 

“The leaf canopy in a forest is very effective in slowing down wind movements because of its large friction area.” 

“The flow beneath a dense canopy is affected only slightly by thermal turbulence, except where holes let the sun strike bare ground or litter on the forest floor.”

This has significant implications for the current fire policy focused on “fuel reductions,” including logging and prescribed burns to protect communities.

A study of 1500 blazes found that high-severity burns were less likely in protected areas like parks and wilderness, where presumably fuels are higher, than in logged areas.

One study concluded: “Airborne embers within plumes can ignite spot fires ahead of a fire front, which along with direct progress of the fire front can contribute to wildfire growth. Embers can fly over firebreaks and other containment methods – like back-burning and aerial fire retardant.”

Wind also allows fires to throw embers over and through “thinning” (logged areas) and prescribed burns, essentially making such “solutions” for precluding large wildfires ineffective.

The famous large wildfires in the West had/have a wind element that created the right conditions for massive blazes.

 Embers lofted by wind are also a primary culprit in home and structure ignitions near wildfires. We have seen this in numerous places.

Human-caused blazes, including 97% that threatened homes, spread much faster and kill more trees than ones ignited by lightning since many starts occur during dry, windy conditions, which favors rapid fire spread.

The 2021 Dixie Fire, which charred over 900,000 acres in California, was largely wind-driven. The Holiday Farm Blaze in Oregon’s Cascades was wind-driven. The 2024 Park fire, which started in a city park in Chico, burned primarily through grass and shrublands and grew 4-5,000 acres per hour. Wind bent over the grass and drove the blaze into the homes at Maui. The Marshall Fire in Colorado and the Smokehouse Blaze in Texas were wind-driven grassland blazes.

One way that thinning (a.k.a. logging) often contributes to fire spread is that opening up the forest canopy enhances the growth of grasses and shrubs, which are a significant culprit in rapid fire spread. Plus, a reduction in tree density also facilitates wind penetration.

The Forest Service handbook, Fire Weather: A Guide For Application Of Meteorological Information, concludes: “The leaf canopy in a forest is very effective in slowing down wind movements because of its large friction area.” 

“The flow beneath a dense canopy is affected only slightly by thermal turbulence, except where holes let the sun strike bare ground or litter on the forest floor.”

Hence, thinning operations enhance fire spread under extreme fire weather conditions with high winds.

The focus on reducing forest density may be misplaced. A study of thousands of homes destroyed by fire concluded, “Rates of structure loss were higher when structures were surrounded by wildland vegetation, but were generally higher in herbaceous fuel types than in higher fuel-volume woody types.” In other words, grass and other “fine fuels” are significant factors determining whether a home will be ignited by wildfire.

A rational approach to wildfire policy would include focusing on home hardening, reducing home construction in the wildlands interface, reducing logging, and ultimately emphasizing reducing climate warming, propelling the current wildfire expansion.