The Footprints of the Largest California Fires Since 2000 1. Mendocino (active)

305,489 acres 1. Mendocino

(active) 2. Cedar, 2003

288,369 acres 2. Cedar

2003 3. Thomas, 2017

281,894 acres 3. Thomas

2017 4. Rush, 2012

271,911 acres 4. Rush

2012 5. Rim, 2013

257,135 acres 5. Rim

2013 6. Witch, 2007

245,582 acres 6. Witch

2007 7. Zaca, 2007

244,448 acres 7. Zaca

2007 8. Klamath Theater, 2008

183,134 acres 8. Klamath Theater

2008 9. Carr (active)

178,752 acres 9. Carr

(active) 10. Station, 2009

168,672 acres 10. Station

2009 11. Basin, 2008

167,199 acres 11. Basin

2008 12. Day, 2006

164,223 acres 12. Day

2006 13. Lime, 2008

159,230 acres 13. Lime

2008 14. McNally, 2002

156,782 acres 14. McNally

2002 15. Rough, 2015

151,536 acres 15. Rough

2015 16. Happy Camp, 2014

133,072 acres 16. Happy Camp

2014 17. Soberanes, 2016

132,123 acres 17. Soberanes

2016 18. Pines, 2002

124,675 acres 18. Pines

2002 19. Simi, 2003

111,464 acres 19. Simi

2003 20. Iron and Alps, 2008

108,930 acres 20. Iron and Alps

2008 21. Shu Lightning, 2008

105,313 acres 21. Shu Lightning

2008 22. Grand Prix, 2003

103,322 acres 22. Grand Prix

2003 23. Harris, 2007

103,170 acres 23. Harris

2007 24. Bar, 2006

102,185 acres 24. Bar

2006 25. La Brea, 2009

99,390 acres 25. La Brea

2009 26. Siskiyou, 2008

97,020 acres 26. Siskiyou

2008 27. King, 2014

96,701 acres 27. King

2014 28. Ferguson (active)

94,885 acres 28. Ferguson

(active) 29. Oak, 2017

91,058 acres 29. Oak

2017 30. Yolla Bolly, 2008

90,753 acres 30. Yolla Bolly

2008 Sources: United States Geological Survey, CalFire

California is in the middle of yet another record-breaking fire season with 820,000 acres across the state already burned — more than twice the area that burned by this point last year.

In the northern part of the state, the Mendocino Complex Fire has grown to more than 300,000 acres, becoming the largest fire ever recorded in California. In fact, three of the largest California fires since 2000 are burning right now.

In addition to the Mendocino Fire, firefighters are battling two more massive blazes in other rural parts of the state. The Carr Fire, near Mount Shasta, has burned more than a thousand homes and caused eight deaths, according to CalFire. And the Ferguson Fire, near Yosemite National Park, is the largest fire in Sierra National Forest history.

Carr Fire California Wildfires Since 2000 Active

Older Mendocino Complex Fire Sacramento Central Valley San Francisco Ferguson Fire CALIFORNIA Thomas Fire 2017 Los Angeles Cedar Fire 2003 San Diego Carr Fire California Wildfires Since 2000 Active

Older Mendocino Complex Fire Sacramento San Francisco Ferguson Fire CALIFORNIA Thomas Fire 2017 Los Angeles Cedar Fire 2003 San Diego California Wildfires Since 2000 Active

Older Carr Fire Mendocino Complex Fire San Francisco CALIFORNIA Thomas Fire 2017 Cedar Fire 2003 Los Angeles Source: U.S. Geological Survey

“The trends are pretty astounding in terms of the number of acres burned, the length of the wildfire season, the numbers of structures lost,” said Kelly Pohl, a research analyst with Headwaters Economics, a nonprofit research group that helps communities develop wildfire plans. “If you look at the trends over several decades, they’ve all gone up.”

In California, 15 of the 20 largest fires in state history have burned since 2000. The state is “a bit like a canary in a coal mine,” Ms. Pohl said. “We are also going to see the same trend across other states in the country in the future.”

A helicopter, left, prepared to drop water on the Ranch Fire, part of the Mendocino Complex Fire, near Clearlake Oaks, California, on Sunday. A chimney, right, was about all that was left standing on Tuesday at a house destroyed in the fire. A helicopter prepared to drop water on the Ranch Fire, part of the Mendocino Complex Fire, near Clearlake Oaks, California, on Sunday. Noah Berger/Agence France-Presse — Getty Images, left; Josh Edelson/Agence France-Presse — Getty Images, right Noah Berger/Agence France-Presse — Getty Images

The rising intensity of wildfires seen over the past few decades is the result of several overlapping trends, said Stephen Pyne, a professor at Arizona State University who studies the history of United States wildfire management. Climate change has lengthened the fire season, housing sprawl is creeping into fire-prone wildland, and fire agencies are struggling to coordinate holistic fire and land management, Dr. Pyne said.

Those trends all converge in California. The state is especially vulnerable — with its high population density, recent prolonged drought, and abundant fire-prone forests and shrubland.

Fires in California account for about 10 percent of all acres burned in the United States since 2000, according to figures from the National Interagency Fire Center. Only Alaska, which is four times larger than California, has seen more acres burn since 2000.

This fire season is poised to be one of California’s worst ever, and it comes on the heels of 2017, which itself had several record-breaking fires. California’s worst year for fire was 2008, when 1.6 million acres burned, in large part because of a series of severe, dry thunderstorms over two days in June.

Acres Burned in California 1.5 million acres burned 1.4 million acres through full year 0.8 million acres 1 million 1.2 million acres through Aug. 9 500,000 0 1995 2008 2018 1.5 million acres burned 0.8 million acres 1.4 million acres through full year 1.2 million acres through Aug. 9 0 1995 2008 2018 Source: National Interagency Fire Center

Fires are getting worse in California and nationwide because of the human impact on the natural fire cycle, experts say. A study last year from the University of Colorado Boulder found that people were indirectly or directly responsible for 84 percent of wildfires and 44 percent of land unintentionally burned from 1992 to 2012. These fires are often caused by sparked power lines, debris burning, campfires, and arson. The Carr Fire, for example, was caused by a flat tire.

The problem, though, is not only that people start most fires. It’s also that longstanding strategies — to not use planned fires and tree thinning to clear built-up vegetation — have increased the risk of serious uncontrolled fires.

“We have too much bad fire, and it’s burning houses, killing people, doing all kinds of nasty stuff,” Dr. Pyne said, “but we could probably have 10 times, 20 times more good fire before we got back to what it should be.”

The cost of suppressing fires has reached all-time highs, and the burden of that expense combined with the increased threat of wildfire is motivating changes in fire policy at multiple levels of government.

Federal Wildfire Suppression Costs $3 billion $2.9 billion 2 billion 1 billion 0 2017 1985 1995 2005 $3 billion $2.9 billion 2 billion 1 billion 0 2017 1985 1995 2005 Source: National Interagency Fire Center | Note: Dollars are adjusted for inflation.

In recent years, authorities have moved toward working with the natural fire cycle rather than fighting it at any cost. In 2010, California became one of the few states in the country to adopt a mandatory statewide building code to help reduce fire risk in wildfire-prone areas.

In neighboring Arizona, cities are taking the lead. Flagstaff, which sits in the world’s largest ponderosa pine forest, was an early adopter of policies addressing the city’s high wildfire risk head on through fire education, controlled fires and tree thinning.

Paul Summerfelt, the city’s wildfire management officer, has seen how the perception of fire among Flagstaff residents has shifted from “scary” to “necessary.” “People had to work through the idea that cutting trees was O.K., that we could have controlled burns, that the right kind of fire at the right times and in the right place was necessary,” he said.

Today, in the forest surrounding Flagstaff, a different kind of fire is actively burning. The city works with the United States Forest Service to allow some lightning-caused fires to burn and to set low-intensity, controlled fires that follow historical fire behavior. These fires benefit the forest ecosystem, Mr. Summerfelt said, while simultaneously reducing the risk of catastrophic fires like those seen in California.