EXPLAINER: How big are California wildfires, why they've spread quickly?

A fireman at work as LA wildfire spreads/SCREENGRAB

Wildfires that have ravaged Los Angeles in California—the most populous state of the United States—have killed at least 10 people and left a trail of destruction worth billions of dollars.

The BBC reported that the fires, now ranked as the most destructive in LA's history, have left losses already expected to exceed $250bn (£206.2bn).

Some 10,000 homes and other buildings have been burned in the wake of the furious fires in Los Angeles, with nearly 180,000 residents in different neighbourhoods of the city ordered to evacuate.

Aljazeera reported that the fires, which erupted on Tuesday last week, continue to rapidly spread, fuelled by high winds.

The BBC reported that it was terrible timing on the morning of January 6, when life-threatening and destructive windstorms were heading for the northern suburbs of Los Angeles.

The local office of the US National Weather Service published a strongly worded alert at roughly 10:30 am local time.

According to the BBC, at almost that exact moment, a fire erupted in the Palisades neighbourhood of LA.

The fire exploded, followed by other wildfires in nearby areas, razing thousands of homes and other buildings, with Sunset Boulevard now in ruins. 

What started the California wildfires?

The BBC said that as LA authorities begin to piece together what sparked the blazes, the speed with which those first flames became raging, rapidly spreading infernos is symptomatic of something happening far more widely.

The first fire started in the Pacific Palisades neighbourhood of Los Angeles at 10:30 a.m. last Tuesday, according to the California Department of Forestry and Fire Protection.

Investigators are still trying to find out the exact trigger for the worst firestorm in recent memory, but a combination of factors might have created conditions optimal for a fire.

California generally experiences wildfires during June and July, and they can run until October, but the blaze has defied the calendar this year, erupting in January—the coldest of the winter months.

 The BBC reported that Southern California, the site of the fires, has been experiencing drought conditions and has not seen significant rainfall for months.

The US Drought Monitor’s latest map shows that as of December 31, 2024, 40.9 percent of California is drought-free.

Last year around this time, as of January 2, 2024, 96.65 per cent of California was drought-free.

Climate change has contributed to an increase in the frequency, season length and burned area of wildfires, according to a report by the US Environmental Protection Agency (EPA).

Dry conditions aided by Santa Ana winds—dry and hot winds common in the area—could have caused the wildfires.

The dry desert air that moves from the interior of the region towards the coast and offshore also contributes to wildfires because it significantly reduces humidity in the environment due to its dry nature.

This causes vegetation to become very dehydrated and susceptible to fire. Under these circumstances, any spark can start a fire, be it from a cigarette butt, vehicle, or power line.

How furious?

Gusts up to 100mph (160km/h) were recorded at higher elevations on Tuesday night, according to AccuWeather meteorologist Danielle Ehresman.

Besides dry vegetation, Los Angeles has other flammable materials, such as low-hanging power cables and wooden telephone poles.

At the outset, the Santa Ana winds, as they are known—strong and gusty winds that blow from inland towards the coast—reached speeds of 80mph (129km/h), supercharging the inferno.

Disastrously, the high winds prevented some firefighting helicopters and planes from taking to the skies in order to dump water on the burning areas.

Santa Ana winds have been associated with extreme wildfires in California in the past, including the Woolsey fire in November 2018, which killed three people and razed 1,600 structures.

Experts, however, warn that weather conditions are dire this year.

Known as the Föhn or Föhnwind in the Alpine regions of Germany, Austria, and Switzerland, Santa Ana winds are associated in folk belief with a range of symptoms including migraines, depression, sleeplessness, confusion, and an increased risk of accidents.

More fires spread rapidly

Reuters reported that the fire started in Palisades, located on the Pacific Ocean, and from there the blaze spread rapidly to other neighbourhoods.

The second fire broke out in Eaton at about 6pm on Tuesday.

A third fire, called the Hurst fire, also broke out the same day in Sylmar, in the San Fernando Valley northwest of Los Angeles.

Five more fires broke out in California on Wednesday: the Lidia, Sunset, and Woodley fires in Los Angeles; the Olivas fire in Ventura; and the Tyler fire in Riverside.

On Friday it was reported that a new fire—the Kenneth fire—had also broken out in West Hills, a neighbourhood in the San Fernando Valley.

Disastrously, the high winds prevented some firefighting helicopters and planes from taking to the skies to dump water on the burning areas.

Climate change

The conditions come against the backdrop of climate change, which is not only increasing the risk of wildfires around the world but also making them particularly explosive.

This is when relatively small blazes rapidly "blow up" so suddenly and with such ferocity that they become difficult to control.

In California, the risk of such extremely fast-growing fires has increased by an estimated 25% due to human-caused climate change, according to some models.

Rising temperatures and prolonged periods of drought are stripping vegetation and dead plant material of their moisture, meaning when a fire does start, there can be no stopping it.

Matt Jones, an Earth system scientist at the University of East Anglia who studies the impact of climate change on wildfires, told BBC that, in 2022 and 2023, LA received extraordinary amounts of rain.

Some 52.46in (133cm) of precipitation hit downtown LA during this period, which was nearly a record.

That excessive rain helped plants in the area to grow but then, in 2024, the weather changed.

Last year was extremely dry in contrast to the previous two years. It means that there is currently a large volume of dried-out vegetation scattered around southern California.

"We're left with a really explosive situation," said Jones.

The BBC reported that climate change is creating hotter conditions in some locations where Santa Ana-like winds occur, meaning that the impact or potential consequences—especially in terms of rapidly escalating wildfires—are worsening.

Survival in California

According to the BBC, insurers have gradually backed away from the state in recent years, cutting the number of policies available to homeowners, though last month the California Department of Insurance issued a landmark regulation that aimed to make insurance more accessible.

Some residents have also been looking into ways to attempt to fireproof their homes.

Those with the greatest resources might take inspiration from the Getty Villa, a museum in the Pacific Palisades. The museum was originally built by J Paul Getty, an early 20th-century oil tycoon.

Staff routinely trim trees and shrubs in the gardens to ensure there is no excess vegetation available to provide fuel for fires.

The building's galleries also have double walls, and staff can control, to some extent, the flow of hot air into the villa via the air conditioning system.

But the fact that fires can leapfrog for several miles makes containment difficult.

Embers from burning vegetation can be whipped up and carried by the wind, allowing new fires to ignite some distance away.

The BBC said that rather than catching fire from direct contact with flames, many homes begin to burn due to embers that can fly miles, entering through eaves or gable vents.

Homeowners can replace porous vents with fire-resistant ones designed to keep out windswept embers and install ember-resistant gutter guards that allow rainwater but stop vegetation from piling up on the roofline.

Despite the grandeur of some LA mansions, however, many were left ravaged by the recent fires – including multiple homes belonging to celebrities. The biggest wildfires could likely overwhelm even the most fortified properties.