Runaway summer forest fires this year in the U.S. Southwest were no surprise to SFI External Professor John Rundle, a distinguished professor of physics and geology at UC Davis. Large fires are a natural consequence of over-controlling fires for more than a century, he says.
The evidence is in the mathematics, Rundle says. Fires naturally follow a mathematical rule called a power law, which, simply expressed, means that there are lots of small fires and relatively few large fires. The proportion between small and large fires varies from one area to another, though, and this variability is reflected in a single number called the scaling factor.
In northern Mexico, for example, the scaling factor is a big negative number, so there are very few big fires and very many small ones. Just across the border in Southern California, however, the scaling factor is a smaller negative number, tilting the balance toward big fires.
The two regions are similar in almost every respect -- weather, plants, topography -- except for one: “In northern Mexico they let the fires burn,” he says, “and the vegetation doesn't build up.” And sparser vegetation makes for smaller fires.
His latest research, published in an article in Physical Review E together with his student Mark Yoder and others, shows this dynamic in a beautifully simple model.
“There has been a history from the early days of suppressing all fires,” Yoder says. “But our model suggests that by being more creative in the use of our resources, possibly by letting small fires burn early in the season, we may be able to significantly mitigate our fire risk and be much safer.”
Read the article in the SFI Update (September/October issue)
Read the Physical Review E paper