Saturday, December 9, 2023

What the complex mathematics of fire modeling tells us about the future of California’s forests

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Pioneer scientists like Rothermel addressed this intractable problem by ignoring it. Instead, they looked for factors, such as wind speed and slope, that could help them predict a fire’s next move in real time.

Looking back, Finney says, it’s a miracle that Rothermel’s equations work for wildfires. There’s the difference in scale: Rothermel derived his equations of tiny, controlled fires in 18-inch fuel beds. But there are also more fundamental mistakes. Most blatantly was Rothermel’s hypothesis that fire spreads only by radiation, instead of passing through the convection currents you see when a campfire flickers.

This assumption is not true, and yet for some fires, even the biggest ones like Northwest Oklahoma Resort in 2017, which burned more than 780,000 acres, Rothermel’s propagation equations still seem to work. But at certain scales and under certain conditions, fire creates a new type of system that defies any attempt to describe it.

The California Creek fire, for example, wasn’t just big. It created a plume of hot air that pooled under the stratosphere, like steam against the lid of a pressure cooker. Then he jumped at 50,000 feet, sucking in air from below that ignited the flames, creating a storm system – with lightning and tornadoes of fire – where no storm should have been.

Other huge and destructive fires seem to ricochet over time, or against each other, in chaotic ways. The fires usually subside at night, but in 2020, two of California’s biggest descents broke out at night. As the heat increases, fires usually burn uphill, but Bear fire, two huge flaming heads traveled 22 miles downhill, a line of tornadic plumes spinning between them.

Finney says we don’t know if the intensity caused the weird behaviors or vice versa, or if both came from a deeper dynamic. According to him, a measure of our ignorance is that we can’t even trust it: “It would be really nice to know when our current models will work and when they won’t,” he says.


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