Drought and lightning are making for a combustible combination in California. The state is suffering through its fourth straight summer of drought, and this may be known as the summer of smoke.

A staggering 10,000 national, state and local firefighters are battling fires that are popping up by the hundreds each week, the majority of which are sparked by lightning strikes from daily thunderstorms erupting over mountainous terrain, which drop little rain and cause a lot of trouble. To put the number of firefighters into perspective, that is about the number of troops the U.S. has in Afghanistan. So far, one firefighter has died fighting California's blazes.

As of Tuesday morning, 22 large uncontained fires were still burning across the state, with the biggest and most destructive one being the Rocky Fire located in Lake County, California, about 100 miles northeast of San Francisco. The Rocky fire grew in size to more than 101 square mile, or about 65,000 acres, on Tuesday, taking advantage of abundant vegetation that had not burned in years.

The fire was just 12% contained as of Tuesday morning, according to the California Department of Forestry and Fire Protection (CalFire).

"Tinder dry conditions from the drought continue to allow wildfires to burn at an explosive rate," CalFire said in an August 4 fire summary.

So far this year, California has seen a whopping 5,916 wildfires, which have charred 148,782 acres. CalFire says it has responded to more than 4,200 of these fires, which is about 1,500 more than the average for the year so far.

With daily thunderstorms popping up across California and the West more broadly, lightning strikes are igniting more blazes that can quickly grow amid gusty winds and tinderbox dry conditions on the ground.

National fire preparedness level increases as more resources called in

The fire conditions in California, Oregon and Washington, all states that have seen record warm temperatures and dry conditions during the past several months or more, have prompted the National Interagency Fire Center in Boise, Idaho, which coordinates wildfire response efforts nationwide, to increase the national preparedness level to "PL4" as of Monday afternoon.

The scale only goes up to PL5, which is the highest preparedness level.

"This decision was due to an increase in fire activity in California, Oregon and Washington, the commitment of resources to large fires, and current and expected weather conditions in the West," NIFC said on its website. At the PL4 level, three or more geographic areas of the country are experiencing wildfires that require high levels of response from federal firefighting crews, known as "incident management teams."

In total, about 3,200 firefighters are combatting the Rocky Fire alone, with thousands more crews deployed nationwide, mainly in the West and Alaska. CalFire estimates that the fire may be contained by August 10, based on forecast conditions and firefighter deployment.

The Rocky Fire has destroyed 24 homes and threatens thousands more. About 13,000 people have been evacuated near the fire's perimeter.

Firefighters tried and failed to stand their ground against the blaze on Monday, as the fire jumped a highway that had served as a containment line despite cooler weather and higher humidity. Its rapid growth area shocked residents.

Vicki Estrella, who has lived in the area for 22 years, stayed at a Red Cross shelter at Middletown High School with her husband and their dog.

"It's amazing the way that thing spread," Estrella said, according to the AP. "There was smoke 300 feet in the air."

According to Daniel Berlant, the chief CalFire spokesman, the Rocky Fire has grown big enough to "create its own weather patterns," sucking air into it from all directions and growing in more than one direction. This is complicating firefighting efforts. "It starts burning in whatever direction it wants to," CalFire spokesman Daniel Berlant said in a Monday morning situation update video.

CA Fire Summary for 8/3 PM UPDATE - 21 active wildfires in California with over 9,000 firefighters on the frontlines. http://t.co/IHpYaFjIXX — CAL FIRE PIO Berlant (@CALFIRE_PIO) August 4, 2015

On a national level, the number of fires is running below the 10-year average of 47,022 for the year-to-date, according to NIFC. So far, there have been 36,754 blazes, as of Tuesday morning. However, the acres-burned-to-date has been above average, with nearly 6 million acres burned so far this year, compared to the year-to-date average of nearly 4 million acres.

Climate change makes bad fire seasons worse

Climate science research has documented changes in wildfire size across the West, and projections show a likelihood that future fire seasons will feature larger fires as spring arrives earlier, vegetation dries out, and droughts become more frequent and severe in some areas.

According to the National Climate Assessment, a federal report released in 2014, decreased spring snowpack and streamflows and increased drought are expected to lead to more and bigger wildfires across the Southwest.

"Increased warming, drought, and insect outbreaks, all caused by or linked to climate change, have increased wildfires and impacts to people and ecosystems in the Southwest," the report said. "Fire models project more wildfire and increased risks to communities across extensive areas."

The report cited studies showing a projected doubling of burned area in the southern Rockies, with average fire frequency increasing by 37% to 74% in California alone.

Climate factors driving increased wildfire risks include hotter temperatures, reduced snowpack, earlier spring warmth and lower streamflow, the assessment said. The changes include increased temperatures, reduced snowpack, earlier spring warmth, and streamflow. Other changes driving increased risks of wildfire include decades of fire suppression policies that created more vegetation available to burn, increased building of homes and businesses in fire-prone areas.

Average statewide temperature in California so far in 2015 compared to other years. 2015 and 2014 are circled. Image: NOAA NCEI

"Multivariate analysis of wildfire across the Western U.S. from 1916 to 2003 indicates that climate was the dominant factor controlling burned area, even during periods of human fire suppression," the assessment stated. "Reconstruction of fires of the past 400 to 3000 years in the western U.S., and in Yosemite and Sequoia National Parks in California, confirm that temperature and drought are the dominant factors explaining fire occurrence."

While scientists are confident that there is a link between global warming and an increase in Western wildfires, there is disagreement on whether climate change triggered the ongoing California drought, which actually extends to the Pacific Northwest and parts of the Rocky Mountain states as well.

The drought, like most historical droughts across the West, may have had its roots in natural fluctuations in sea surface temperatures across portions of the Pacific and Atlantic Oceans. However, most research-to-date shows that hotter temperatures due to climate change have worsened the ongoing drought, and these temperatures are playing a role in the fire season as well.

In California, for example, 2014 was the state's warmest year on record, a milestone likely to be repeated this year, since temperatures so far are running hotter than they did during the same period in 2014. In the Pacific Northwest, Seattle has broken its record for the most 90-degree Fahrenheit days in an entire summer, and numerous locations have tied or broken all-time heat records.

Seattle also set a record for its driest May 1 through July 31 period on record.

In fact, the entire Western U.S. is having its warmest year on record so far, according to data from the National Oceanic and Atmospheric Administration (NOAA), and depicted in the graphic below.

Average temperatures across the West for January-to-June 2015 (top right) compared to all previous years of record-keeping. Image: NOAA/NCEI

Unfortunately, until the rainy season starts — which could be wetter than average thanks to an El Niño event in the tropical Pacific Ocean — it's likely that wildfire conditions will continue to deteriorate across the West, straining fire crews and putting residents' nerves on edge. While an unusually wet winter will certainly help alleviate some of the drought conditions, since 2012, California has racked up a statewide average surface water deficit of about 20 inches, which is a years' worth of precipitation.

The rainfall deficit is even worse when one considers the depletion of groundwater, which farmers have tapped to make up for the lack of water for irrigation. Factoring that in, the deficit is more like two years' worth of rain or more.

Additional reporting by the Associated Press