Want to Fight the Zombie Fire Apocalypse? Weaponize Math

The largest fires on Earth aren’t the monsters that have been burning across California and Australia , but the zombies smoldering in the soils of the Arctic and tropics. Undead fires live on in peat: wet, carbon-rich soil made from dead vegetation that accumulates over hundreds or even thousands of years. When it dries out—as it is increasingly doing on a warming planet—peat fires can fester, slowly spreading both laterally and vertically for months and releasing astonishing amounts of greenhouse gases . In the Arctic, which is warming twice as fast as the rest of the planet, peat fires even smolder under the snow throughout winter and reanimate in the spring, alighting as new surface wildfires. Hence, zombie fires.

Since they’re much less conspicuous than your typical wildfire, the dynamics of peat fires have been a bit of an enigma for scientists—for instance, how do they spread? Where do they end up in the landscape? How quickly do the fires propagate? But some clever new modeling, known as cellular automata, is giving fire scientists unprecedented insight into the life, spread, death, and rebirth of zombie fires. That could help firefighters better predict where the zombies might later emerge.

“The magic of cellular automata is that by aggregating very simple rules in a space, it actually is able to capture what is called an ‘emergent behavior,’ which is a behavior that is extremely complex,” says Imperial College London engineer Guillermo Rein, coauthor of a new paper describing the work in the journal Proceedings of the Combustion Institute. “You can do what is called ‘super real-time’—in the sense that you get results of the future location of the fire before the fire is already there. If you want to help firefighters predict the movement of a fire, you have to have super real-time.”

How the spread of a peat fire looks in infrared.

Courtesy of Imperial Haze Lab
The modeling works like this: The researchers first partition a stretch of imaginary peat into square cells—think of it like a sheet of graph paper. Each of these cells is given simple states: For instance, does it contain fuel or not? (In this case, the fuel is sufficiently dry peat.) And has a cell burned yet? Cells of course border one another, and thus influence each other’s states as the fire spreads. This comes with certain probabilities—maybe a cell has a high probability (say, 95 percent) or a low probability (say, 5 percent) of also burning when any of its neighbors are. “It's very simple rules,” says Rein. “One: If the nearby cells are burning with a probability, you start burning. And when you're burning after X amount of minutes, you stop.”