The best way to measure fire risk might be underground Swati Mestri Scientific Editor Andrew Zinin Chief Editor When fire risk is high, Arizonans know the major warning signs: hot temperatures, low humidity and lots of wind. But there's one fire factor we don't fully understand: soil moisture. Salli Dymond, an associate professor in NAU's School of Forestry, said measuring moisture levels in the soil and in forest plants—fire's potential fuel—could prove key to preventing or containing some of the most catastrophic wildfires in the Southwest and beyond.

This summer, Dymond is working with Salt River Project (SRP) and the startup company Growvera to install moisture sensors on plants and dead fuel on the forest floor and underground throughout the southeastern Tonto National Forest. Over the course of a year, she and her colleagues will monitor the sensors and analyze the data they generate. Dymond said that if the sensors provide accurate enough moisture data, they could become a game changer in how Arizona officials communicate about and prepare for wildfire season.

"New studies have shown that using soil moisture in conjunction with fuel moisture will bring all the pieces of the puzzle together," Dymond said. "It could help us understand how dry the forest fuels are, how dry the soils are and how stressed the plants are from hour to hour. That way, we can make real-time decisions about road and forest closures, fire stage warnings and fire suppression right from our computers, without having to drive out and observe these conditions." Why soil moisture?

Today, experts in Arizona predict fire risk by gathering and interpreting weather data such as humidity, temperature and wind speed. Dymond said that while the current system works, it misses the full picture. "We collect weather data out in the open and in a few locations, and it's not always indicative of on-the-ground conditions," she said.

"Many times, our wildfires ignite under complex terrain where the plants are interacting not only with the weather but also with below-ground moisture. So, the moisture of the soil and the fuels growing in it is really a better indicator of what the conditions are like on the ground." Measuring soil and fuel moisture used to be expensive, but sensors have become much more affordable in the past 10 years. That's where Growvera comes in, Dymond said.

The New Mexico startup has developed a cheaper alternative to traditional plant moisture sensors, and it's working with Dymond and SRP to test its product's efficacy. If the sensors work well, it's a win-win: Growvera can market its sensors, backed by research success, to forest managers, and the Southwest can stay safer from catastrophic wildfires. "I think Growvera and I have the same goal, which is to get this into the hands of practitioners who can benefit from it," Dymond said.

Hyperlocal data This month, Dymond and her colleagues traveled to sites in Tonto National Forest and attached Growvera's Chip Clip–like sensors onto dead trees, healthy trees and other wildfire fuel sources like dead twigs and branches. They also buried soil moisture sensors—these look like tiny fans and are manufactured by a different company—at different depths underground.