Författare: David Bowman Professor of Pyrogeography and Fire Science Uni

For centuries, fire was one of the major fears for city-dwellers. Dense cities built largely of wood could – and did – burn. In 1666, a fire in a bakery went on to destroy two-thirds of the city of London, leaving 85% of residents homeless. In 1871, fire burned out huge areas of Chicago. In World War II, bombing raids by Allied forces largely destroyed cities such as Dresden in Germany and Tokyo in Japan.

The threat of large-scale urban fires drove authorities to spend more on urban firefighting and require buildings to use less flammable material. Fire alarms, fire engines and automatic sprinklers have done much to reduce the chance of uncontrolled spread.

But will our sense of safety endure in the age of climate change? In January, we saw swathes of Los Angeles burn – even in the northern winter. Driven by low humidity and high winds, numerous large fires encroached on the city, destroying outlying suburbs. Climate change made the fires worse, according to climate scientists.

Now we have new research on the question of whether climate change will make large city fires more likely. A research team from China, Singapore and Australia have gathered a decade’s worth of data on fires from almost 3,000 cities in 20 nations, home to one-fifth of the world’s population.

The researchers found for every 1°C increase in air temperature, outdoor fires (rubbish and landfill) increase 4.7% and vehicle fires 2.5%. If the world accelerates its burning of fossil fuels under a high emissions scenario compatible with a 4.3°C temperature rise by century’s end, outdoor fires in cities would soar 22% and vehicle fires 11%. But building fires are projected to actually fall 5%. Thankfully, this emissions scenario is now less likely.

The Great Fire of London destroyed most of the city in 1666.
HodagMedia/Shutterstock

What did this research find?

To make these findings, the researchers aggregated the fire incident data from 2,847 cities located in 20 countries over the 2011–20 decade and analysed them to see how air temperature influences the frequency of three types of fires: outdoor, structural and vehicle. They found a strong correlation.

Of the 20 nations, New Zealand looks likely to have the highest increase in fires, soaring 140% over 2020 figures by 2100.

When we think of fires in a city, we usually think of structural fires – a building going up in flames.

The research suggests building fires would actually decrease 5% by 2100. This is unexpected, and might suggest uncertainty about this finding.

Interestingly, this research found the fewest structural fires occurred at air temperatures of 24°C, a temperature which humans find optimal. When it’s hotter or cooler than that, more buildings catch fire.

Why? It’s likely due to our behaviour. We spend more time indoors when it’s very cold or very hot outside, which the authors suggest could make us more likely to accidentally cause fires by using electrical appliances and fireplaces which have a fire risk.

By contrast, outdoor and vehicle fires do increase linearly as temperatures rise. Most vehicle fires come from an equipment or heat source failure, which are both likely to increase as temperatures rise. We are also more likely to have a car crash when it’s hotter, and vehicle fires often come after a crash.

Vehicle fires will become more common as the climate changes, according to this research.
Rodrigo Teixeira/Pexels, CC BY-NC-ND

Outdoor fires become more likely because heat dries out fuels and favours fire spread. Rubbish dumps can spontaneously catch fire when temperatures are too high – even underground. This happens because chemical reactions are accelerated in warmer temperatures, causing waste materials to heat up faster. If the extra heat isn’t dissipated, waste can become so hot that it catches fire on its own.

We should take these estimates with a grain of salt. This is because they project recent statistical patterns into an uncertain future, and draw on a data set not perfectly suited to the task. The data set stops in 2020, before the electric vehicle transition gathered speed. EVs have a different risk profile for accidental fires.

As the authors note, there are large barriers to getting a coherent understanding of fire risk. “Despite multiple efforts, we have been unsuccessful in obtaining fire data from Africa and South America,” they write.

Their estimates also relate to a high-emissions future which is hopefully becoming less likely, though the general pattern of the results are similar under less severe climate projections.

Most importantly, it’s not yet clear why temperature influences urban fires. This uncertainty raises questions over whether simple projections of current patterns into the future are realistic or appropriate.

Cities aflame?

Arguably the most important contribution of this new research is to show us that our cities are not inherently protected from fire.

For city authorities, this research points to the need to manage combustible materials, from piles of mulch to dry urban parks and even home gardens. Storage yards, rubbish dumps and recycling centres will also need to be managed.

Fire used to be a major concern for cities, and it could be again. Cities and fire are uneasy bedfellows, and climate change will worsen the situation. Läs mer…

Tasmania has been burning for more than two weeks, with no end in sight. Almost 100,000 hectares of bushland in the northwest has burned to date. This includes the Tarkine rainforest and alpine ecosystems of Cradle Mountain that may never recover.

The situation has taken emergency services and land management agencies by surprise. The seasonal bushfire outlook for summer 2024 suggested Tasmania’s fire risk was nothing out of the ordinary. The state was also well prepared for bushfire fighting, particularly with specialised aircraft.

But this fire season has turned out to be anything but typical. Firefighting capacity has been stretched to the limit and interstate crews have been called in.

It all began with a massive lightning storm in the evening of Monday February 3. The incidence of such lightning fires has been increasing in Tasmania since the 1990s.

An official inquiry into the bushfires will no doubt be held, given the substantial social, economic and environmental harm – as well as the sizeable costs associated with fighting the fires from the air in remote and rugged landscapes.

Nonetheless, important lessons are emerging from these fires, which speak to the broader, worsening threat as the climate changes.

Understanding the impacts of the fires

Fortunately, direct economic losses from theses fires have been limited so far, despite significant disruption associated with evacuation and road closures. Tourism operators and honey producers have been hardest hit.

The fires caused brief but substantial smoke pollution across the state, placing a range of people with medical conditions at risk.

The full environmental effects and the benefits of prescribed burning are yet to be evaluated. Nonetheless, there is grave concern about damage to unique rainforests and alpine ecosystems. If sufficiently dry the organic soils, or peats, that supports forests and treeless areas in western Tasmania are also vulnerable to combustion.

We undertook a preliminary estimate of how much highly fire-sensitive vegetation – plant communities that will take more than 50 years to recover – may have burned. This involved comparing the current bushfire boundaries or footprint, based on satellite data and field reconnaissance, to vegetation mapping used for various purposes including fire management. We put the figure at 19,716 hectares of vegetation. However, it’s possible not all of this burned and islands of unburned vegetation persist within the broad fire boundary.

Our estimation includes 10,419 hectares of temperate rainforest (10% of the fire area) and 462 hectares of alpine vegetation (0.45% of the fire area). Neither of these vegetation types can readily tolerate fire.

Our analysis suggests about half of fire-affected rainforest areas have been previously burned by fires since 1982 (48%) and some small areas have burned twice (5%). Recurrent fires in rainforest can result in permanent loss of this vegetation. Just how much damage has been done will require further assessment.

Current area affected by bushfires in northwestern Tasmania, comparing data from Geoscience Australia on bushfire boundaries and Land Information Services Tasmania on vegetation. Note, not all of the shaded area has burned.
Grant Williamson

Emergence of new fire patterns

The number of fires ignited by lightning have increased in Tasmania since the 1990s. When the lightning occurs in storms without much rain, or where the rain evaporates before it hits the ground, it’s known as dry lightning.

Concerningly, in the last decade two other major dry lightning fire events have occurred,
likely a signal of a change in fire activity. As a result, fires are burning into areas that historically are rarely affected by fire, damaging the natural values of the Tasmanian wilderness.

This event could not be predicted

Going into summer, experts were concerned that soils across western Tasmania were particularly dry. This increased the fire risk in the seasonal outlook.

The recent rapid fire growth in Tasmania was caused by the unusual combination of regional drying (including dry soils), an extreme lightning storm and subsequent strong winds.

But the sequence of events that caused this fire to take off could not have been predicted more than a week ahead. That’s because it is impossible to predict lightning and windstorms outside the seven-day window of weather forecasts.

What’s more, our research shows it is currently not possible to reliably predict which lightning strikes will start fire.

By February 12, more than a dozen fires had burned around 50,000 hectares in the state’s northwest.
NASA Earth Observatory

Rapid attack and fire suppression have practical limits

Massive lightning storms that ignite multiple fires overwhelm the capacity of firefighters to locate and immediately extinguish all the flames.

Unfavourable weather conditions caused the west coast fires to rapidly grow. Firefighting shifted from attempts to extinguish the fire to instead contain its spread. This involved techniques such as targeted waterbombing, back burning and building fire breaks.

These approaches have been successful in some cases, notably the deployment of retardant drops to contain the Canning Peak fire, saving extensive stands of conifer rainforest. But suppression efforts were imperfect, as the loss of a private tourist facility hut on the Overland Track has demonstrated.

Managing these massive fires demands triage – making difficult choices about where to direct firefighting effort. Effective triage requires a detailed understanding of the location of areas of high economic, cultural and environmental value. High-quality mapping of these sites and involvement of specialists in the broader decision-making process is essential.

The Tasmanian government does have maps and expertise to guide triage, but there are calls for more investment to protect the region’s ecological values. This is particularly important for small, localised sites vulnerable to fire, such as groves of ancient Huon pine.

Fires continue to burn in Tasmania’s west, putting wilderness areas at risk (7.30)

Broader lessons for fire fighting

Dry lightning storms are hard to predict, extraordinarily difficult to contain, and can cause substantial economic, social and environmental harms.

Technology alone – such as that which combines satellites, artificial intelligence, drones and water bombers – is not enough to eliminate these fires. What’s needed is a diverse portfolio of approaches, involving a combination of:

reducing fuel loads by prescribed burning
firefighting that is carefully targeted using high quality data
expertise embedded in firefighting teams.

Researchers and fire managers must also identify the best strategies for prescribed burning to reduce bushfire risk while protecting areas of high economic, conservation and cultural value.

Climate change will bring more frequent monster fires – and fighting them demands a broad suite of investment. Läs mer…