It’s not ‘traditional’ wildfire season – so why have the California fires spread so quickly?

A real-life drama is unfolding just outside Hollywood. Ferocious wildfires have ballooned at an “alarming speed”, in just a matter of hours. Why?

What caused the California wildfires?

There are currently three wildfires torching southern California. The causes of all three are still being investigated.

The majority (85%) of all forest fires across the United States are started by humans, either deliberately or accidentally, according to the US Forest Service.

But there is a difference between what ignites a wildfire and what allows it to spread.

However these fires were sparked, other factors have fuelled them, making them spread quickly and leaving people less time to prepare or flee.

The main culprit so far is the Santa Ana winds.

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What are Santa Ana winds?

So-called Santa Ana winds are extreme, dry winds that are common in LA in colder winter months.

The California Department of Forestry and Fire Protection warned strong Santa Ana winds and low humidity are whipping up “extreme wildfire risks”.

Winds have already topped 60mph and could reach 100mph in mountains and foothills – including in areas that have barely had any rain for months.

It has been too windy to launch firefighting aircraft, further hampering efforts to tackle the blazes.

These north-easterly winds blow from the interior of Southern California towards the coast, picking up speed as they squeeze through mountain ranges that border the urban area around the coast.

They blow in the opposite direction to the normal onshore flow that carries moist air from the Pacific Ocean into the area.

The lack of humidity in the air parches vegetation, making it more flammable once a fire is started.

The ‘atmospheric blow-dryer’ effect

The winds create an “atmospheric blow-dryer” effect that will “dry things out even further”, said Daniel Swain, a climate scientist at University of California, Los Angeles (UCLA).

The longer the extreme wind persists, the drier the vegetation will become, he said.

“So some of the strongest winds will be at the beginning of the event, but some of the driest vegetation will actually come at the end, and so the reality is that there’s going to be a very long period of high fire risk.”

What role has climate change played?

California governor Gavin Newsom said fire season has become “year-round in the state of California” despite the state not “traditionally” seeing fires at this time of year – apparently alluding to the impact of climate change.

Scientists will need time to assess the role of climate change in these fires, which could range from drying out the land to actually decreasing wind speeds.

But broadly we know that climate change is increasing the hot, dry weather in the US that parches vegetation, thereby creating the fuel for wildfires – that’s according to scientists at World Weather Attribution.

But human activities, such as forest management and ignition sources, are also important factors that dictate how a fire spreads, WWA said.

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Southern California has experienced a particularly hot summer, followed by almost no rain during what should be the wet season, said Professor Alex Hall, also from UCLA.

“And all of this comes on the heels of two very rainy years, which means there is plenty of fuel for potential wildfires.

“These intense winds have the potential to turn a small spark into a conflagration that eats up thousands of acres with alarming speed – a dynamic that is only intensifying with the warmer temperatures of a changing climate.”

The flames from a fire that broke out yesterday evening near a nature reserve in the inland foothills northeast of LA spread so quickly that staff at a care home had to push residents in wheelchairs and hospital beds down the street to a car park.