A California firefighter was arrested Friday morning after allegedly setting five fires in wine country during what has already been a bad year for wildfires in the state.

Robert Hernandez, a 38-year-old fire apparatus engineer with Cal Fire, the state’s main firefighting agency, was arrested on suspicion of setting fires on forest land near the Northern California towns of Geyserville, Healdsburg and Windsor between Aug. 15 and Sept. 14.

The fires remained small, burning less than an acre of land combined, because local residents and firefighters worked quickly to extinguish them, according to Cal Fire. Mr. Hernandez, a resident of Healdsburg who was accused of setting the fires while off duty, was booked into the Sonoma County Main Adult Detention Facility on six felony counts and was being held on $2 million bail.

“I am appalled to learn one of our employees would violate the public’s trust and attempt to tarnish the tireless work of the 12,000 women and men of Cal Fire,” Joe Tyler, the director and fire chief of Cal Fire, said on Friday.

Cal Fire law enforcement officers took Mr. Hernandez into custody and have arrested 923 arson suspects since 2016.

A 2016 report by the National Volunteer Fire Council determined, based on media accounts, that more than 100 firefighters in the United States were arrested each year on arson charges. The report said that they represented a tiny percentage of the nation’s firefighters, and that motives varied, from those who wanted to be a hero by putting out their own blazes to others who wanted more firefighting action or suffered from psychological disorders.

Cases of “firefighter arson” have occurred for centuries, the fire council said.

Nearly 1 million acres have burned in California so far this year, almost three times the total last year. Just this month, firefighters have been battling three large blazes in Southern California that have burned dozens of homes and other structures. Favorable weather conditions in recent days have helped them gain the upper hand.