Wildfires can be terrifying – Image: Manny Beccera/Unsplash
Much of Australia enjoys the same Mediterranean climate as LA. When it comes to bushfires, that doesn’t bode well.
The world has watched in horror as fires continue to raze parts of Los Angeles, California. For those of us living in Australia, one of the world’s most fire-prone continents, the LA experience feels all too familiar.
A “perfect storm” of several factors resulted in the catastrophic fires now burning in Southern California: long-term climate change combined with extreme weather conditions, all playing out in one of the most densely populated parts of the United States.
The tragedy offers valuable lessons for other global cities in a similar climate zone to Los Angeles – including the Australian centres of Adelaide and Perth. The fires are also instructive for centres such as Sydney and Melbourne, where the climate is warming and drying.
That’s why, in Australia, it’s important to understand how climate drivers played out before and during the LA wildfire emergency. Some are naturally occurring and others are the result of global warming. So let’s look at them in more detail.
The all-consuming Californian wildfire disaster – Image: Daniel Lincoln/Unsplash
How climate change fuelled the LA fires
As global temperatures increase, Earth’s water cycle is changing. Over the past 50 years, this has led to an expansion of Earth’s tropical and subtropical zones. Tropical areas are moist and lush, but dry at the northern and southern edges.
These dry edges are pushing towards the poles. Regions that used to enjoy a gentler Mediterranean climate, as shown in the map below, are turning into dry subtropical zones.
They include highly populated regions, such as Southern California. Similarly, parts of Australia including Perth and much of southeast Australia has dried in recent decades, in a pattern consistent with tropical expansion.
As the shift continues, winter rainfall in these regions is largely declining. In the case of California, this decline has mostly occurred in southern areas of the state which are closer to the dry subtropical edge.
The expansion of the tropics means rainfall in California has also become more erratic. Since the 1980s it has endured years of abnormally high rain and snow, followed by years of very low rain and snow. This variability has been dubbed “climate whiplash”.
The exceptionally wet years fuelled widespread vegetation growth. This growth shrivelled in the dry years, providing ample fuel for the wildfires.
Of further concern for California, the proportion of rain versus snow has increased in the Sierra Nevada and Southern Cascades regions of the state.
This has reduced the amount of water stored in the snowpack – water crucial to California’s water supply.
In most years, global warming is reducing the amount of precipitation that falls as snow.
In recent months, the Los Angeles region has been extremely dry and drought had been declared across the county.
So what does all this mean for Australia? Perth and Adelaide both have Mediterranean-type climates, and research suggests they will eventually become dry subtropics.
Both cities have warmed since the 1970s. Perth has dealt with a significant decline in rainfall and Adelaide has had a moderate decline.
The climate of Melbourne and Sydney has historically been classed as “warm temperate” rather than Mediterranean, with some rain in all months of the year. But both have experienced warming and moderate drying since the 1980s.
If current climate trends continue, by 2100 the edge of the new dry subtropical zone would extend across the continent in a rough band from Sydney to Perth.
The role of La Niña
El Niño and La Niña are complex weather patterns driven by changes in ocean temperatures in the Pacific. An unusually late La Niña has just been declared.
During La Niña years, the eastern Pacific (including California) typically experiences below-average rainfall, while the western Pacific (including eastern Australia) has above-average rainfall. The converse generally occurs in El Niño years.
La Niña usually brings drought to Southern California. On this occasion, that part of the state was already very dry. This is consistent with the “climate whiplash” effect described above.
As others have noted, in early January the soil moisture in much of Southern California was in the bottom 2% of historical records. This dryness helped propel the fires.
During an El Niño, Australia typically becomes hotter and drier, and the bushfire risk increases. We saw this with the Black Summer fires in 2019–20, which followed the 2018–19 El Niño.
The notorious Santa Ana winds
The Santa Ana winds are a natural phenomenon that typically occur during the southern California autumn and into January. They rush from the top of the San Gabriel Mountains, in northern Los Angeles County, and head towards the coast, warming and drying the landscape.
The canyons and steep cliffs in the Los Angeles region also drive these gusty winds across exposed areas of land – many densely populated.
The Santa Ana winds occur at least ten times a year. But before and during the wildfires they reached hurricane strength. Most years, autumn rainfall reduces the wildfire risk associated with these winds. But as noted above, this year Los Angeles was in severe drought.
Australia does not have a direct equivalent to the Santa Ana winds. But the continent does experience hot, dry winds much larger in scale. They originate from the arid centre and blow towards the coast, often driving bushfires.
And mega-fires can become so powerful they generate their own wind systems, pushing fire rapidly across the landscape into populated areas.
Fire disasters on a large scale are more likely in future as climate change worsens – Image: Polina Kuzovkova/Unsplash
What all this means for Australia
The horrific fires in California may be rare. But disasters of this scale are likely in future as climate change worsens. Most Mediterranean climate regions will experience a 5–10% decline in precipitation this century. That increases the bushfire risk.
Human-caused climate change is driving more intense and frequent extreme weather globally. The LA wildfires occurred because climate change warmed and dried the region, disrupting natural climate variations.
Around the world, including Australia, authorities must find ways to adapt to the new climate normal – building community resilience to the devastating disasters which are, tragically, now inevitable.
Steve Turton, Adjunct Professor of Environmental Geography, CQUniversity Australia
(NAN 14-01-25 – This article is republished from The Conversation under a Creative Commons license. Read the original article)
