Climate change - fires intensify after flash droughts

 

Flash droughts pull ‘alarming’ amounts of moisture from the landscape and intensify wildfires: new research

Abhirup Dikshit, UNSW and Jason Evans, UNSW

When catastrophic wildfires capture global headlines, such as the unprecedented blazes sweeping through southern Europe this summer or the devastating 2019–20 “Black Summer” in Australia, they are almost always preceded by severe drought. Dry vegetation and parched landscapes are necessary ingredients for infernos.

But not all droughts are created equal – the way a drought evolves can drastically alter how a fire behaves once it ignites. As global temperatures rise, a new and dangerous phenomenon is becoming increasingly common: the “flash drought”.

Unlike standard droughts, which take place over months or years, flash droughts are rapidly occurring dry spells, driven by intense heat and unusually low humidity. They suck moisture out of the landscape at an alarming rate.

While scientists know standard droughts increase fire risks, a critical question has remained unanswered: do flash droughts further increase this risk, and what happens when these two drought types collide?

Our latest research mapped two decades of global satellite data to answer this question. We found when landscapes transition from a prolonged standard drought into a rapid flash drought – or when the two overlap – they create a “hyper-flammable” state. This acts as a massive fire accelerant; they spread faster, last longer and grow significantly larger than other wildfires.

How hyper-flammability works

To understand why this happens, we have to look at how different droughts affect the environment. The major difference is the speed at which they occur.

A standard drought acts like a slow, relentless oven. Over months, it gradually dries out vegetation and severely reduces soil moisture, leaving a dry environment primed to burn.

A flash drought, on the other hand, is like hitting the landscape with a high-powered hairdryer. The atmospheric dryness rapidly increases, characterised by extreme heat and low humidity, and quickly depletes remaining soil moisture.

When a standard drought turns into a flash drought, the effects don’t just add up; they multiply. Combined, they cause the fire danger to skyrocket, setting the perfect stage for fast-spreading and intense wildfires. Short-lived weather anomalies such as flash droughts generate disproportionately severe and extreme fires.

Tracking two decades of global fires

To uncover this pattern, we analysed global drought and satellite-based fire data sets from 2002 to 2021. Global wildfires were categorised into four distinct groups: fires occurring under normal (no drought) conditions; fires occurring during flash droughts; fires occurring during isolated standard droughts; and fires occurring where the two drought types overlapped or followed one another.

Across every single fire metric we measured, including speed, size, duration and spread, fires burning under combined drought conditions were the most extreme. The median size of these fires was 65% larger than fires in normal conditions, and 21% larger than those occurring during standard droughts alone. They spread 35% faster and burned 19% longer.

We also discovered that regions experiencing combined drought conditions endured significantly longer dry spells before a fire actually started. On average, 72 days passed between the onset of a combined drought and the start of a fire. This compared with only 17 days for flash droughts and 56 days for standard droughts. This prolonged period allows severe dryness to develop before fires start.

Global fire hotspots

While fires that follow standard droughts are widespread across the globe’s arid and semi-arid zones, we found fires following flash droughts and, particularly, combined droughts, clustered in distinct geographic hotspots.

The most extreme are heavily concentrated in highly vulnerable communities of plants and animals, including the savannas of South America and Africa, northern Australia, and the western United States.

These regions are highly susceptible to rapid-onset heat and moisture stress, making them ground zero for compounding climate extremes. The presence of both slow-moving and flash droughts causes the most extreme fire behaviour, thus amplifying the fire’s intensity.

Rethinking wildfire preparation

As the climate continues to heat up, the rate of evaporation increases worldwide. This means the frequency and extent of combined droughts are likely to increase across fire-prone regions around the world.

Crucially, we must stop viewing droughts simply as a static state of reduced moisture. Instead, we must recognise them as evolving processes, in which the shift from one type of drought to another can fundamentally change wildfire severity.

Unfortunately, many current global drought and fire monitoring systems emphasise real-time conditions, or look at drought severity as an aggregated whole. To better protect communities and nature, these systems urgently need to integrate information on how droughts evolve. This would enable us to better detect emerging hyper-flammable landscapes before the first spark.

Abhirup Dikshit, ARC DECRA Fellow, Climate Change Research Centre, UNSW and Jason Evans, Professor, Climate Change Research Centre, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate Change and increasing wildfires worldwide

The climate crisis is fuelling extreme fires across the planet

Hamish Clarke, The University of Melbourne

We’ve all seen the alarming images. Smoke belching from the thick forests of the Amazon. Spanish firefighters battling flames across farmland. Blackened celebrity homes in Los Angeles and smoked out regional towns in Australia.

If you felt like wildfires and their impacts were more extreme in the past year – you’re right. Our new report, a collaboration between scientists across continents, shows climate change supercharged the world’s wildfires in unpredictable and devastating ways.

Human-caused climate change increased the area burned by wildfires, called bushfires in Australia, by a magnitude of 30 in some regions in the world. Our snapshot offers important new evidence of how climate change is increasing the frequency and severity of extreme fires. And it serves as a stark reminder of the urgent need to rapidly cut greenhouse gas emissions.

The evidence is clear – climate change is making fires worse.

A view of the Palisades fire zone in Los Angeles, where climate change fuelled the fires in January. Allen J. Schaben/Getty

Clear pattern

Our study used satellite observations and advanced modelling to find and investigate the causes of wildfires in the past year. The research team considered the role that climate and land use change played, and found a clear interrelationship between climate and extreme events.

Regional experts provided local input to capture events and impacts that satellites did not pick up. For Oceania, this role was played by Dr Sarah Harris from the Country Fire Authority and myself.

In the past year, a land area larger than India – about 3.7 million square kilometres – was burnt globally. More than 100 million people were affected by these fires, and US$215 billion worth of homes and infrastructure were at risk.

Not only does the heating climate mean more dangerous, fire-prone conditions, but it also affects how vegetation grows and dries out, creating fuel for fires to spread.

In Australia, bushfires did not reach the overall extent or impact of previous seasons, such as the Black Summer bushfires of 2019–20. Nonetheless, more than 1,000 large fires burned around 470,000 hectares in Western Australia, and more than 5 million hectares burned in central Australia. In Victoria, the Grampians National Park saw two-thirds of its area burned.

In the United States, our analysis showed the deadly Los Angeles wildfires in January were twice as likely and burned an area 25 times bigger than they would have in a world without global warming. Unusually wet weather in Los Angeles in the preceding 30 months contributed to strong vegetation growth and laid the foundations for wildfires during an unusually hot and dry January.

In South America, fires in the Pantanal-Chiquitano region, which straddles the border between Brazil, Bolivia and Paraguay, were 35 times larger due to climate change. Record-breaking fires ravaged parts of the Amazon and Congo, releasing billions of tonnes of carbon dioxide.

Protestors march for climate justice and against wild fires affecting the entire country in Sao Paulo, Brazil. Faga Almeida/Getty

Not too late

It’s clear that if global greenhouse gas emissions continue to rise, more severe heatwaves and droughts will make landscape fires more frequent and intense worldwide.

But it’s not too late to act. We need stronger and faster climate action to cut fossil fuel emissions, protect nature and reduce land clearing.

And we can get better at responding to the risk of fires, from nuanced forest management to preparing households and short and long-term disaster recovery.

There are regional differences in fires, and so the response also need to be local. We should prioritise local and regional knowledge, and First Nations knowledge, in responding to bushfire.

Action at COP30

Fires emitted more than 8 billion tonnes of carbon dioxide in 2024–25, about 10% above the average since 2003. Emissions were more than triple the global average in South American dry forests and wetlands, and double the average in Canadian boreal forests. That’s a deeply concerning amount of greenhouse pollution. The excess emissions alone exceeded the national fossil fuel CO₂ emissions of more than 200 individual countries in 2024.

Next month, world leaders, scientists, non-governmental organisations and civil society will head to Belem in Brazil for the United Nations annual climate summit (COP30) to talk about how to tackle climate change.

The single most powerful contribution developed nations can make to avoid the worst impacts of extreme wildfires is to commit to rapidly cutting greenhouse gas emissions this decade.

Hamish Clarke, Senior Research Fellow, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.