Flames rise over a cluster of homes in Oak Hills on July 17.

Flames rise over a cluster of homes in Oak Hills on July 17.

A helicopter prepares to drop water over a fire near Oak Hills, California, on July 17.

A helicopter prepares to drop water over a fire near Oak Hills, California, on July 17.

The scorched remains of a truck destroyed by the North Fire are towed away near Victorville on July 17.

The scorched remains of a truck destroyed by the North Fire are towed away near Victorville on July 17.

Smoke from a wildfire rises above Interstate 15 near San Bernardino, California, on July 17.

Smoke from a wildfire rises above Interstate 15 near San Bernardino, California, on July 17.

The North Fire burns July 17 near Interstate 15 in the Cajon Pass in San Bernardino County.

The North Fire burns July 17 near Interstate 15 in the Cajon Pass in San Bernardino County.

Slow-moving traffic fills the northbound lanes of Interstate 215 near Victorville, California, on Friday, July 17. The traffic was linked to the North Fire, which caused people to abandon their vehicles and flee as flames jumped the freeway.

Slow-moving traffic fills the northbound lanes of Interstate 215 near Victorville, California, on Friday, July 17. The traffic was linked to the North Fire, which caused people to abandon their vehicles and flee as flames jumped the freeway.

Flames from the Pines Fire burn on Saturday, July 18, in Wrightwood, California. The blaze was burning near Mount San Antonio, which is also called Mount Baldy for its snow-capped summit that's highly visible in Los Angeles.

Flames from the Pines Fire burn on Saturday, July 18, in Wrightwood, California. The blaze was burning near Mount San Antonio, which is also called Mount Baldy for its snow-capped summit that's highly visible in Los Angeles.

A firefighting aircraft drops retardant on a ridge to combat the Wragg Fire on July 23.

A firefighting aircraft drops retardant on a ridge to combat the Wragg Fire on July 23.

Trees and brush burn while firefighters battle the Wragg Fire near Winters, California, on Thursday, July 23. The fast-moving wildfire had scorched almost 7,000 acres in Napa and Sonoma counties, authorities said.

Trees and brush burn while firefighters battle the Wragg Fire near Winters, California, on Thursday, July 23. The fast-moving wildfire had scorched almost 7,000 acres in Napa and Sonoma counties, authorities said.

As the Rocky Fire approaches, goats run from their pen after firefighters freed them on July 31.

As the Rocky Fire approaches, goats run from their pen after firefighters freed them on July 31.

A firefighter prepares to douse spot fires in Lower Lake on July 31.

A firefighter prepares to douse spot fires in Lower Lake on July 31.

Firefighters spray a hose at a fire near Lower Lake on July 31.

Firefighters spray a hose at a fire near Lower Lake on July 31.

Heat marks are visible on an air-conditioning unit at a destroyed home in Lower Lake on August 1.

Heat marks are visible on an air-conditioning unit at a destroyed home in Lower Lake on August 1.

A firefighting air tanker flies in front of the setting sun while battling the Rocky Fire on August 1.

A firefighting air tanker flies in front of the setting sun while battling the Rocky Fire on August 1.

Large plumes of smoke rise from the Rocky Fire on Saturday, August 1.

Large plumes of smoke rise from the Rocky Fire on Saturday, August 1.

Flames from the Rocky Fire burn through dry grass August 2 near Clearlake.

Flames from the Rocky Fire burn through dry grass August 2 near Clearlake.

The Rocky Fire burns near Clearlake on August 2.

The Rocky Fire burns near Clearlake on August 2.

Firefighters light backfires in an attempt to control the blaze near Clearlake on August 2.

Firefighters light backfires in an attempt to control the blaze near Clearlake on August 2.

A Cal Fire truck is driven away from flames as the Rocky Fire burns near Clearlake on August 2.

A Cal Fire truck is driven away from flames as the Rocky Fire burns near Clearlake on August 2.

Firefighters look on as the Rocky Fire burns through trees on Sunday, August 2.

Firefighters look on as the Rocky Fire burns through trees on Sunday, August 2.

Flames from a backfire operation burn through a grove of trees as firefighters try to head off the Rocky Fire on Monday, August 3, near Clearlake, California.

Flames from a backfire operation burn through a grove of trees as firefighters try to head off the Rocky Fire on Monday, August 3, near Clearlake, California.

A burn operation is seen during the Jerusalem Fire, near Lower Lake, California, on Friday, August 11.

A burn operation is seen during the Jerusalem Fire, near Lower Lake, California, on Friday, August 11.

A crew descends a scorched mountainside in the Angeles National Forest on August 15.

A crew descends a scorched mountainside in the Angeles National Forest on August 15.

A plane drops fire retardant on the Cabin Fire north of Asuza, California, on Saturday, August 15.

A plane drops fire retardant on the Cabin Fire north of Asuza, California, on Saturday, August 15.

Firefighters hose down the smoldering ruins of a building that was burned by the Warm Fire north of Castaic, California, on Sunday, August 16.

Firefighters hose down the smoldering ruins of a building that was burned by the Warm Fire north of Castaic, California, on Sunday, August 16.

Firefighter Mike Martel walks through smoke while working to clean up after a weekend fire that ravaged the Montebello Hills area near Los Angeles on Monday, August 17.

Firefighter Mike Martel walks through smoke while working to clean up after a weekend fire that ravaged the Montebello Hills area near Los Angeles on Monday, August 17.

A firefighter climbs on the side of a hill while putting out hot spots in Livermore on August 20.

A firefighter climbs on the side of a hill while putting out hot spots in Livermore on August 20.

The charred remains of a property is seen in Livermore on August 20.

The charred remains of a property is seen in Livermore on August 20.

Fires burn on a hill in Livermore, California, on Thursday, August 20. California has been battling numerous wildfires as its historic drought reaches a fourth year.

Fires burn on a hill in Livermore, California, on Thursday, August 20. California has been battling numerous wildfires as its historic drought reaches a fourth year.

About

Wildfires are sometimes called "wildland fires."

Wildfires can originate from a dropped match, cigarette embers, campfires, exhaust sparks from a train, or arson. Many wildland fires are ignited by lightning.

There are no official rules, but the first responders usually name a fire after a meadow, creek, city, or type of plant they see.

Wind, temperature and humidity all influence wildfires. Strong winds push flames toward new fuel sources. Wind can pick up and transfer burning embers and sparks, starting "spot fires."

During the day, sunlight heats the ground and warm air rises, allowing hot air currents to travel up sloped landscapes. At night, the ground cools and air currents travel down the slopes.

Humidity dampens fuel, slowing the spread of flames. Humidity is greater at night, so fires usually burn less intensely then.

Large fires can create their own winds and weather, increasing their flow of oxygen. A really large fire can generate hurricane-force winds, up to 120 mph.

The National Interagency Fire Center lists wildfire fatalities from from 1910 to the present.

Largest monetary wildland fires losses are ranked by the Insurance Information Institute.

US Fire Season Summary

(National Interagency Fire Center)

2010

Fires: 71,971 Acres Burned: 3,422,724

2011

Fires: 74,126 Acres Burned: 8,711,367

2012

Fires: 67,774 Acres Burned: 9,326,238

2013

Fires: 47,579 Acres Burned: 4,319,546

2014

Fires: 63,312 Acres Burned: 3,595,613

2015

Fires: 68,151 Acres Burned: 10,125,149

2016

Fires: 67,743 Acres Burned: 5,509,995

2017

Fires: 71,499 Acres Burned: 10,026,086

2018

Fires: 58,083 Acres Burned: 8,767,492

2019

Fires: 50,477 Acres Burned: 4,664,364 71,9713,422,72474,1268,711,36767,7749,326,23847,5794,319,54663,3123,595,61368,15110,125,14967,7435,509,99571,49910,026,08658,0838,767,49250,4774,664,364

Structures Destroyed by Wildfires, by Year

(National Interagency Coordination Center)

2010 - 788 structures destroyed: 338 residences, 445 outbuildings and five businesses. The annual average (since 1999) is 1,179 residences, 1,156 outbuildings and 42 businesses. 788 structures destroyed: 338 residences, 445 outbuildings and five businesses. The annual average (since 1999) is 1,179 residences, 1,156 outbuildings and 42 businesses.

2011 - 5,246 structures destroyed: 3,459 residences, 1,711 outbuildings and 76 commercial structures. The annual average is 1,354 residences, 1,199 outbuildings and 45 commercial structures. 5,246 structures destroyed: 3,459 residences, 1,711 outbuildings and 76 commercial structures. The annual average is 1,354 residences, 1,199 outbuildings and 45 commercial structures.

2012 - 4,244 structures destroyed: 2,216 residences, 1,961 outbuildings and 67 commercial structures. The annual average is 1,416 residences, 1,253 outbuildings and 46 commercial structures. 4,244 structures destroyed: 2,216 residences, 1,961 outbuildings and 67 commercial structures. The annual average is 1,416 residences, 1,253 outbuildings and 46 commercial structures.

2013 - 2,135 structures destroyed: 1,093 residences, 945 outbuildings and 97 commercial structures. The annual average is 1,394 residences, 1,233 outbuildings and 50 commercial structures. 2,135 structures destroyed: 1,093 residences, 945 outbuildings and 97 commercial structures. The annual average is 1,394 residences, 1,233 outbuildings and 50 commercial structures.

2014 - 1,953 structures destroyed: 1,038 residences, 874 minor structures, 20 commercial structures and 14 mixed commercial/residential structures. The annual average is 1,372 residences, 1,210 minor structures and 49 commercial structures. 1,953 structures destroyed: 1,038 residences, 874 minor structures, 20 commercial structures and 14 mixed commercial/residential structures. The annual average is 1,372 residences, 1,210 minor structures and 49 commercial structures.

2015 - 4,636 structures destroyed: 2,638 residences, 29 multiple residences, 1,849 minor structures, 111 commercial structures and nine mixed commercial/residential structures. The annual average is 1,449 residences, 1,248 minor structures and 53 commercial structures. 4,636 structures destroyed: 2,638 residences, 29 multiple residences, 1,849 minor structures, 111 commercial structures and nine mixed commercial/residential structures. The annual average is 1,449 residences, 1,248 minor structures and 53 commercial structures.

2016 - 4,312 structures were destroyed: 3,192 residences, 1,025 minor structures, 78 commercial structures and 17 mixed commercial/residential structures. The annual average (since 2015) is 1,449 residences, 1,248 minor structures and 53 commercial structures. 4,312 structures were destroyed: 3,192 residences, 1,025 minor structures, 78 commercial structures and 17 mixed commercial/residential structures. The annual average (since 2015) is 1,449 residences, 1,248 minor structures and 53 commercial structures.

2017 - 12,306 structures were destroyed: 8,065 residences, 4,002 minor structures, 229 commercial structures and 10 mixed commercial/residential structures. The annual average (since 2016) is 1,545 residences, 1,236 minor structures and 55 commercial structures. 12,306 structures were destroyed: 8,065 residences, 4,002 minor structures, 229 commercial structures and 10 mixed commercial/residential structures. The annual average (since 2016) is 1,545 residences, 1,236 minor structures and 55 commercial structures.

2018 - 25,790 structures were destroyed: 18,137 residences, 6,927 minor structures and 229 commercial/residential structures. The annual average (since 2017) is 2,701 residences, 1,379 minor structures and 64 commercial/mixed residential structures. The number of structures destroyed in 2018 is more than twice the 2017 figure. 25,790 structures were destroyed: 18,137 residences, 6,927 minor structures and 229 commercial/residential structures. The annual average (since 2017) is 2,701 residences, 1,379 minor structures and 64 commercial/mixed residential structures. The number of structures destroyed in 2018 is more than twice the 2017 figure.

2019 - 963 structures were destroyed: 444 residences, 482 minor structures and 37 commercial/residential structures. The annual average (since 2018) is 2,593 residences, 1,600 minor structures and 94 commercial/mixed residential structures. 963 structures were destroyed: 444 residences, 482 minor structures and 37 commercial/residential structures. The annual average (since 2018) is 2,593 residences, 1,600 minor structures and 94 commercial/mixed residential structures.