Who caused the LA fires? Blame swirls amid tragedy.

Authorities don't yet know what started the wildfires that forced tens of thousands of Californians from their homes, but politicians, residents and experts have already begun to assign blame for the tragedy.

Scientists have noted the fires met their ideal weather and geographic conditions for maximum destruction this week: Dry vegetation, high winds and low humidity were all fuel.

Osbee Sangster, who evacuated the Eaton Fire to the Pasadena Convention Center, was among residents critical of the response from local officials. On Wednesday, she said she was “disappointed in how today was handled by the fire department.” She recalled seeing fire trucks mandating evacuations, but echoed concerns about first responders running out of water to fight the fires. “Where was the water?”

Meanwhile, politicians ? including President-elect Donald Trump ? have pointed fingers at California's elected leaders, accusing them of not being prepared for these fires.

All this as answers remain elusive about the ignition source of the fires. While officials had suspected one of the blazes was arson, the allegation against a suspect was determined to be unfounded, officials said.

Here's a look at what we know about the causes of the fires:

Latest updates: 10 dead, 10K structures destroyed as LA fires turn neighborhoods into ash

How extreme fire weather helped flames spread

A combination of extreme Santa Ana winds up to 100 mph, dry vegetation and low humidity made the entire region prime for extreme fire behavior, forecasters warned leading up to the outbreak of the first major fires on Tuesday.

Santa Ana winds typically push dry air from the inland deserts of California and the Southwest toward the coast, the National Weather Service said. The winds blow over the mountains, and become compressed and warmed up.

The hot, dry winds further dry out vegetation that already saw little recent rainfall. That vegetation becomes wildfire fuel. Any ember can easily be carried far and wide by the winds, spreading flames quickly and with little to stop them.

The critical fire weather conditions are ongoing Friday as firefighters work to contain the blazes, the weather service said.

More: What caused the LA fires to spread so rapidly?

Los Angeles' geographic makeup

The areas of the county impacted by fire for the most part sit at the edge of mountain regions, making them more prone for fire behavior.

Steep slopes, canyons and valleys around the Santa Monica and San Gabriel mountains help the fire in two ways. First, because heat rises, it can essentially pre-heat vegetation up hills, which helps the fires spread uphill quickly, Yale University research scientist Jennifer Marlon said. Second, canyons and valleys can act as funnels for the Santa Ana winds.

Why is this happening?: 3 reasons California's wildfires got so dangerous so fast

Politicians pointing fingers

Trump and his allies blamed California Gov. Gavin Newsom, other Democratic officials and environmentalists. The former president has long criticized Newsom for his forest management policies, claims his opponents called misleading.

Meanwhile, Los Angeles Mayor Karen Bass is also under fire for being out of the country on an official trip when the fires broke out and her response since. She didn't answer questions on Thursday about her initial absence.

"Rest assured that ... when that is done, when we are safe, when lives have been saved and homes have been saved, we will absolutely do an evaluation to look at what worked, (and) what didn't work," she said at a news conference.

"Probably both of them are just stone-cold incompetent," Trump said of Newsom and Bass on Thursday speaking from his Mar-a-Lago resort in Florida.

"The Governor is focused on protecting people, not playing politics, and making sure firefighters have all the resources they need,” Izzy Gardon, Newsom's communications director, told USA TODAY in a statement.

Water problems

One of the challenges firefighters faced in battling the blazes was a shortage of water in fire hydrants. On Thursday, President Joe Biden said that part of the reason was that local utilities "understandably shut off power because they were worried that the lines that carried energy could be blown down and spark additional fires."

"But when they did that, it cut off the ability to generate pumping water," the president said. He added that CalFire, the state’s fire prevention agency, was bringing in generators to get the pumps moving again.

At the same time, "there were so many hydrants that were being used all at once," said California Rep. Judy Chu.

Los Angeles Department of Water and Power CEO Janisse Qui?ones said by 3 a.m. Wednesday, the city utility’s three 1-million-gallon water storage tanks in the Palisades area "went dry," reducing the water flow from hydrants in higher elevations.

"We pushed the system to the extreme. Four times the normal demand was seen for 15 hours straight, which lowered our water pressure," Qui?ones said. "It was like a worst-case scenario, but I think we should be planning for those worst-case scenarios."

What does climate change have to do with it?

Experts say that more frequent and intense wildfires will result from overall rising temperatures due to human-caused climate change.

"Climate change is leading to larger and more severe wildfires in the western United States," the National Climate Assessment previously reported. These fires have “significant public health, socioeconomic, and ecological implications for the nation.”

In California, though the Santa Ana winds and dryness are sometimes par for the course, climate change is leading to fire season starting earlier and ending later, according to CalFire. Longer and more intense dry seasons make forests more susceptible to severe wildfires.

"November, December, now January — there’s no fire season, it’s fire year," Gavin Newsom said earlier this week. "It’s year-round."

Contributing: Doyle Rice, Karissa Waddick, Ignacio Calderon, Michael Loria, Natalie Neysa Alund, Christopher Cann, N'dea Yancey-Bragg and Terry Collins, USA TODAY; McKenna Mobley, USA TODAY Network; Reuters

This article originally appeared on USA TODAY: Who caused the LA fires? Blame swirls amid tragedy.