San Juan National Forest Fuels Crew Supervisor Vince Mowery is deep in the forest above Dolores clipping Gambel oak and snowberry bushes, pulling off pine needles, grabbing a handful of forest duff and sawing off pieces of dead wood, called “cookies.”
He carefully places the different samples into round metal cans, weighs them on a scale from the tailgate of his truck, then heads off to an oven in a garage at the Dolores Public Lands Office.
“Testing fuel moisture levels is what we do when not fighting wildfires,” Mowery said. “We depend on the data to plan for the fire season so we are prepared when wildfire risk is high.”
In the Dolores Ranger District of the San Juan National Forest, different trees, bushes and deadwood are tested at six sites of varying elevations every two weeks from April to November. The sites are at Boggy Draw, the Dolores Canyon Rim, Lowry Ruin, Stinking Springs, Haycamp Mesa and Taylor Mesa.
The data collected is critical for understanding the level of wildfire risk, potential fire behavior, whether conditions are right for a prescribed burn and the level of planning needed for the fire season.
“We would be running blind without fuel moisture data,” Mowery said.
When moisture is trending low, the forest can staff up with firefighters from wetter parts of the country. Wildfire risk in the San Juans continues to be significant, based on low fuel moisture levels, officials said. A hard drought and lack of monsoons this year are to blame.
When a bent pine needle cracks instead of flexing, conditions are dry.
Right now, all the vegetation is stressed by drought. Officials urge extreme caution in the forest.
The Severe Fire Weather Potential Index also is a measure of wildfire risk in Southwest Colorado, and helps illustrate the late wildfire season. As of Oct. 20, the potential energy release of a wildfire in the region had a rating of 93 out of 110. The average energy release potential for this date is a rating of 58.
After Mowery weighs the samples, they are cooked for 24 hours and weighed again. The difference in weight determines the fuel moisture content of the sample. It is then compared with a chart showing likely fire behavior should the sample location catch fire.
When fuel moisture content is high, fires do not ignite readily, or at all, because heat energy has to be used to evaporate and drive water from the plant before it can burn. When the fuel moisture content is low, fires start easily and will spread rapidly — all of the heat energy goes directly into the burning flame itself.
If moisture is 181% and higher, fires will exhibit very low fire behavior. From 126% to 150%, fires will be moderate; and from 75% to 100%, fires will show extreme behavior.
As the drought continues, fuels are becoming drier, further increasing wildfire potential.
On Oct. 16, samples of Utah juniper from the testing sites averaged 66% moisture content, down from an average of 74% moisture content on Aug. 30.
The drop elevated fire risk to the highest level of “advanced fire behavior,” up from “extreme fire behavior.”
“Advanced fire behavior” has the potential to dominate the landscape and consume large amounts of acreage in a very short time.
On Oct. 16, the average moisture content for ponderosa pine from the six sites was 96%, down from 104% on Sept. 14.
The drier conditions elevated the fire risk for that species to “extreme fire behavior,” up from “high fire behavior.”
Extreme fire behavior typically brings extreme rates of spread and moderate- to long-range spotting. Engines and bulldozers might be needed to back up fire operations and to protect structures. Fires will burn actively at night.
Monsoonal rains are relied upon to prevent wildfire risk from moving into fall. But they are becoming less reliable.
On Aug. 15, 2010, monsoonal rains brought fuel moisture for ponderosa pines at the Boggy Draw test site to 149%, a moderate fire behavior risk, according to the National Fuel Moisture Database.
On Aug. 15, 2018, when there was not a monsoon in Southwest Colorado, those same Boggy Draw ponderosa trees were at 108% fuel moisture, which is a high fire behavior risk.
Dead fuels are also critical in determining fire potential. The dead fuel moisture threshold is based upon how long it would take for two-thirds of the dead fuel to respond to atmospheric moisture.
Fuel moisture levels of so-called “thousand-hour fuels,” such as dead timber on the forest floor, are a key predictor for wildfire behavior, said Cary Newman, San Juan National Forest fire planner. They do not burn easily, but if they dry out significantly, they generate extreme heat and contribute to dangerous fire conditions.
Fuel moisture for thousand-hour fuels are at historic lows, Newman said, based on a recent analysis of 2001 to 2019 data from three Remote Automated Weather Stations located across Southwest Colorado that are representative of pine woodlands.
“What is most significant is how, in the absence of significant moisture since early September, the calculated 1,000-hour fuel moistures have continued to descend to a point much below prior historical minimums,” Newman said.
This condition is being corroborated with actual fuel moisture sampling.
The analysis showed that as of Oct. 15, 1,000-hour fuels in Southwest Colorado pinelands were estimated to be at 10% or lower, and the average for the that date over a 20-year period is 15%.
“Fuel moisture data is very useful and helps us model fire behavior across landscapes,” Newman said.
When 1,000-hour fuels are below 10%, wildfires exhibit intensity and are resistant to control.
“We need persistent, frequent moisture to recover,” he said.
He added that drier conditions in the West are contributing to larger and hotter wildfires, which increases demand for a limited supply of federal firefighting resources.
