Eight large wildfires are now burning across Oregon, with the largest topping 100,000 acres, according to the Northwest Interagency Coordination Center.

That brings the total number of large wildfires — defined as 100 acres or more in timberland or 300 acres or more in grassland – to 22 this year in Oregon. By July 14 last year, there had been only 12, according to officials.

Last week’s heat wave, which pushed temperatures up to 110 degrees in some parts of the state, likely played a role in the number of fires that have broken out this past week, said Oregon Department of Forestry spokesperson Andy Dwyer.

“These heat spells that come in dry the fuel out even more,” he said.

Dwyer also pointed to lower humidity levels and high winds as key factors.

The largest of the fires currently burning — the Cow Valley fire — started last Thursday about nine miles east of Ironside in eastern Oregon and has grown to 132,528 acres. More than 300 firefighters and other personnel have been deployed to the fire, which is 0% contained, according to Cow Valley Fire Information.

To the south, another human-caused fire rages on in Harney County. The Falls fire, also completely uncontained, reached 64,225 acres as of Monday morning. That fire also has more than 600 total personnel fighting it, the Harney County Sheriff’s Office reported.

Now at 1% containment, the Lone Rock fire that started over the weekend in Gilliam County grew to more than 50,000 acres by Monday morning, according to the Northwest Interagency Coordination Center. One hundred eighty-nine people have fought the fire thus far.

Crews made some progress on the Larch Creek fire that started last Tuesday near Dufur, reaching 11% containment. The blaze is now 18,684 acres and is expected to cost well over $8 million, according to the interagency center.

Lead agencies overseeing the other three fires have not yet released estimated costs. Three of the four fires are human-caused.

The Oregon State Fire Marshal has resources on all four fires, which are the largest ones currently burning, said agency spokesperson John Hendricks.

“Our system is getting to a point where there’s a little bit of stress on it right now,” Hendricks said.

He added that all three of the agency’s incident-management teams have been deployed to the fires.

Kassidy Kern, Central Oregon Fire Info spokesperson, described a similar challenge facing that agency, which is currently battling the Larch Creek and Lone Rock fires.

“If the [Lone Rock fire] were the only incident in the area, we might be able to put more focus on it,” she said. But resources are “stretched thin” because of the number of fires raging across the state, Kern continued.

The state brought in out-of-state firefighters to help combat some of the blazes, according to an Oregon Department of Forestry press release. Twenty-nine Washington firefighters were sent to the Falls fire, and the Oregon Department of Forestry has deployed more than 58 firefighters from New Mexico, Idaho, Montana, Oklahoma, Texas, Georgia, Colorado and Florida in the last week, department spokesperson Jessica Neujahr said.

Thirteen more firefighters from Florida are expected to arrive in the coming days.

State agencies will have to play a balancing act to make sure each fire has enough personnel, Northwest Interagency Coordination Center spokesperson Robin DeMario said.

“We are trying to utilize all of the resources that we have in the region and distribute them where they’re needed most,” she said.

Dwyer emphasized that many wildfires this year have been human-caused and urged people to be aware that even activities like driving or barbecuing can pose a fire risk.

“If you’re going to be doing anything that could cause an ignition start in an area that’s receptive to fire,” he said, “please take extra precaution.”

— Sujena Soumyanath is a reporter on The Oregonian/OregonLive’s public safety team. You can reach her at 503-221-4309 or ssoumyanath@oregonian.com.