January 8, 2025

expert reaction to LA wildfires

Scientists comment on Los Angeles wildfires.

Prof Apostolos Voulgarakis, Professor in Global Climate and Environmental Change, Imperial College London, said:

“The ongoing wildfires in California are unprecedented, in the sense that they are dramatic for this time of the year – the season that is supposed to feature the lowest fire occurrence in the area.  However, research has shown that the fire season is indeed widening in California as a consequence of climate change.

“The western US in general is an area experiencing climate warming along with rainfall reductions, the combination of which leads to more intense fires.  This trend is only expected to worsen in the future.  The hot and dry Santa Ana winds that often affect the southern California region and fuel large wildfires such as the ongoing one, only make things worse.  Research has shown that the occurrence of Santa Ana winds in the autumn are also likely to get worse with climate change, leading to even drier vegetation, fast fire spread and more intense late-season wildfires.”

Dr Douglas Kelley, Land Surface Modeller, UK Centre for Ecology & Hydrology, said:

What do we know about the current situation?

“California is experiencing significant winter wildfires, fueled by a combination of unusually dry vegetation, high temperatures, and strong offshore winds – winds that are typical for this time of year.  High fire risk in some of these areas were predicted several days in advance.  While traditional methods, such as the fire weather index flagged elevated fire risk across much of California, newer AI models operating at a higher resolution (1 km) provided more precise spatial predictions, pinpointing the specific area where the fire eventually occurred (McNorton et al., 2024).  The proximity of these fires to populated areas has exacerbated their impact.

“While winter fires in this region aren’t rare, this situation is a stark reminder of how multiple factors – dry conditions, abundant vegetation, and strong winds – can create a perfect storm for wildfires.”

Joe McNorton, Scientist, Earth System Modelling Section, European Centre for Medium-Range Weather Forecasts, said:

Do we know why this has happened?

“The fires are driven by several overlapping factors.  California has experienced very low precipitation through autumn and winter, leaving vegetation – both living and dead – exceptionally dry.  This dryness, combined with strong offshore winds and high temperatures, created ideal conditions for fires to spread rapidly.  Importantly, the location of the fire starts near human settlements has amplified the risks.

“These fires are the result of an abundance of both dead and live vegetation in an unusually dry state coupled with strong winds.”

How unusual are these fires in this location and at this time of year?

“Winter wildfires in Southern California are not unusual, especially during the offshore wind season.  However, the combination of prolonged dryness, high temperatures, and the fire’s rapid spread near populated areas makes this event particularly concerning.  Similar conditions fueled the Thomas Fire in December 2017, one of the largest winter fires in California’s history.

“Recent advancements in forecasting now incorporate detailed fuel characteristics, as documented by McNorton and Di Giuseppe (2024)¹.  These improvements enable us to predict fire danger more accurately by factoring in the condition of live vegetation, providing a clearer picture of potential fire risk.  For instance, AI-based models using these new variables are better equipped to anticipate events like the Thomas Fire and the current Palisades wildfire.

“Winter fires are not uncommon in Southern California, but what we’re seeing here highlights how drier conditions and better fire forecasting tools can both warn us about and underscore the severity of these events.”

1 McNorton, J. R. and Di Giuseppe, F.: A global fuel characteristic model and dataset for wildfire prediction, Biogeosciences, 21, 279–300, https://doi.org/10.5194/bg-21-279-2024, 2024.

Comments sent out on Wednesday 8 January 2025:

Dr Maria Lucia Ferreira Barbosa, wildfire scientist, UK Centre for Ecology & Hydrology (UKCEH), said:

“The fires in Los Angeles are a stark reminder of how extreme weather increases fire risk.  It is likely that heavy rains from El Niño last year fuelled vegetation growth, which has since dried out during the recent prolonged dry spell and, along with strong winds, creating perfect conditions for wildfires to spread.

“Unfortunately, the proximity of these fires to urban areas significantly increases the risk to people and property.

“While it is too early to link the current Los Angeles fires to climate change, our research has shown that global warming brings more prolonged dry conditions that exacerbate the spread of wildfires.

“There is projected¹ to be a global increase of extreme fires of up to 14 per cent by 2030, 30 per cent by 2050 and 50 per cent by the end of the century.”

1 https://www.unep.org/resources/report/spreading-wildfire-rising-threat-extraordinary-landscape-fires

Prof Stefan Doerr, Editor-in-Chief of the International Journal of Wildland Fire; and Director of the Centre for Wildfire Research, Swansea University, said:

“Key factors for wildfires are low relative humidity, strong wind and drought.  ‘Fire weather’ refers to the weather conditions that are conducive to wildland fire.  It does not necessarily need to be very warm – however, warm temperatures lead to lower relative humidity.  The low humidity combined with the strong winds ’suck’ further moisture out of the already dry vegetation and increase its flammability.  Once ignited, the strong winds fan the flames.  The situation is made worse by the topography (fires burn more intensely and move more rapidly in steep terrain) and the fact that this area of California is dominated by naturally very fire-prone (i.e. very flammable) shrub vegetation.

“It looks like today is likely to continue with extreme fire behaviour (rapid movement of fire aided by flying embers) given the strong winds and low humidity.

“We know from previous evidence that climate change has already made fire weather more severe and the fire season longer in most regions of the world.  While fires are common and natural in this region, California has seen some of the most significant increases in the length and extremity of the fire weather season globally in recent decades, driven by climate change.

“That said, it is too early to say to what degree climate change has made these specific fires more extreme.  This will need to be evaluated in a more detailed attribution analysis.”

Prof Rory Hadden, Professor of Fire Science, University of Edinburgh, said:

Do we know why this has happened?

“The initial cause of the fire is probably not worth speculating at this time.  The rapid growth is somewhat unusual (but sadly we are seeing it more regularly).  It has been reported that this is due to the dry (low humidity) Santa Ana winds.  The rapid fire growth makes it hard to reach the fires and manage them when they are small, the landscape here – very hilly – is also challenging for fire fighting.

“The fire hazard here in addition to the flames is firebrands.  These are small (or sometimes not so small) burning embers that are blown buy the wind and can land in neighbourhoods and cause ignition of structures.  Many of these are produced from the burning of natural fuels but even more are generated once houses start burning.  This means that the fire spreads from house to house in neighbourhood very fast.  This quickly overwhelms fire fighters.

“Smoke and firebrands can also make escape challenging as visibility is reduced.  There are also evacuation problems as I understand due to limited access (note that this is typical of the areas susceptible to this kind of fire).

“One of the key reasons here is that it is desirable to build in these locations (on the edge of a city, near nature) but this is inherently a higher danger area to live.  Landscapes need to be managed to keep up with evolving fire danger driven by climate change.  This is a huge challenge for governments as there are many political issues associated with management of wild spaces (as well as costs).  California actually already has some great guidance on this but it is difficult to enforce and indeed enact sometimes.

How unusual are these fires in this location and at this time of year?

“Sadly not that unusual and not that unexpected.  Several weather watchers had been reporting high fire danger forecasts.  We are in general good at knowing the drivers of fire danger but it is a huge societal problem of how to prepare and react.”

Dr Kimberley Simpson, Fellow in nature-based climate solutions, University of Sheffield’s School of Biosciences, said:

“A prolonged period of unusually low rainfall, coupled with the arid Santa Ana winds blowing in from inland areas, has created the perfect conditions for disaster: bone-dry vegetation that ignites easily in the parched, low-humidity environment, fueling rapidly spreading wildfires.

“These devastating fires are not only occurring with greater intensity but are also striking earlier than Southern California’s typical fire season, highlighting how climate change is reshaping fire regimes – the characteristic patterns of wildfire in a region.

“While working to slow the effects of climate change and reduce fire risk through strategic vegetation management, we must also adapt to the new ‘normal’ of larger, more intense fire regimes and enhance our preparedness for these escalating challenges.”

Brent Walker, Met Office Expert Meteorologist, said:

“The development of the Santa Ana winds has probably aided the development of the wildfires in the Los Angeles area.  These are not uncommon in winter and tend to develop, in varying degrees of magnitude, when pressure rises strongly, following the passage of weather system across the region.  Santa Ana winds can be very strong, reaching 60-70 mph at times.  The Santa Ana winds also generate very low humidity, with observations in the areas showing between 15 and 20%.  Both strong winds and low humidity aid the spread of wildfires, although don’t necessarily generate them in the first instance.  Winds should begin to ease tomorrow.”

Declared interests

Dr Maria Lucia Ferreira Barbosa: “No interests to declare.”

Prof Stefan Doerr: “I declare no conflict of interest.”

Prof Rory Hadden: “Funding:

National Institute of Standards and Technology;

USDA Forest Service;

Strategic Environmental Research and Development Programme (US Department of Defense);

Scottish Government;

UKRI/EPSRC;

Dstl;

Building Safety Regulator.”

Brent Walker: “Nothing to declare.”

For all other experts, no reply to our request for DOIs was received.