Investigators haven’t identified the cause of two fires that scorched more than 11,000 acres in Napa County last month, but there’s a disturbing commonality to some of the worst wildfires this year in drought-stricken California: human negligence.

In Shasta County, the Bully fire burned more than 12,600 acres, destroyed 20 structures and resulted in one death. The cause? Investigators blame a Sacramento man who parked his truck in dry grass while making a deliver to an illegal marijuana farm.

A vehicle also is blamed for the Sand fire, which has burned 4,200 acres and 19 homes in Amador County since last week.

In April, an illegal campfire ignited a 2,100-acre blaze in the San Bernardino National Forest near Rancho Cucamonga forced the closure of nine schools and the evacuation of 1,500 homes.

Unfortunately, none of these stories is unusual.

About nine in 10 wildfires are caused by people, according to the California Wildland Fire Coordinating Group, a coalition of state and federal emergency response agencies.

We’d like to think people would act more responsibly given all the warnings about heightened fire danger due to the drought.

Clearly, that hasn’t been the case.

Meanwhile, California’s crippling drought keeps getting worse.

For the first time since the federal government started issuing regular drought reports two decades ago, more than half of the state has the most severe ranking, an “exceptional drought.” Add those areas where the drought is classified as “extreme,” and 82 percent of the Golden State is historically parched.

As for the rest — mostly the Mojave Desert and a small portion of the rugged forests in the northwestern corner of the state — the U.S. Drought Monitor says they are withering under a “severe” drought. The state’s reservoirs are low, and its groundwater supplies are declining.

To protect dwindling water supplies, the state Water Resources Control Board authorized fines of up to $500 a day for hosing down sidewalks and other wasteful practices.

Perhaps a similar risk would get the attention of property owners in fire zones.

Cal Fire inspectors found that 18.2 percent of rural property owners in Northern California and 9.7 percent in Southern California ignore state and local laws requiring them to protect their homes from wildfire, according to data reviewed by the Associated Press.

AP found stark regional differences in how Cal Fire enforces preparedness laws: “During the last three fiscal years, inspectors in the southern region conducted about 396,000 defensible-space inspections, compared with about 63,000 in the north. They found more than 29,000 violations, compared with nearly 11,000 in the north.”

As for enforcement, Cal Fire wrote 5,076 citations in its southern divisions, compared with eight in the north.

No one likes paying a ticket, be it a parking violation, speeding or failing to prepare for a wildfire. We’d be pleased if Cal Fire didn’t need to write citations as that would mean people were following laws and guidelines for fire safety.

A 100-foot defensible area is required around homes in fire-prone areas. Firefighting agencies also recommend clearing brush on slopes because wind can push flames quickly up a hill and keeping rain gutters clear of pine needles and other debris. Don’t use brush-clearing machinery on hot days and, in the case of a fire, have a plan for getting away with family members, pets and important documents.