wildfire in Australia are a major cause of human fatalities and damage to the natural landscape. They also threaten many of the country’s species, such as birds and mammals.
In addition, wildfires release carbon dioxide into the atmosphere, fueling climate change. And while bush fires are important for clearing undergrowth and promoting regrowth, the ecosystem can take decades to recover from extreme wildfires.
What is a bushfire?
A bushfire is a wild fire that burns in an Australian forest, woodland, scrub or grassland. They have shaped Australia for millions of years, helping plants and trees adapt to our harsh climate.
Fuel (vegetation) and weather determine how a bushfire will behave, including how fast it will move. Fine fuels like grasses can burn more quickly than more dense, woodier fuels. The speed of a fire also depends on the amount of wind that's blowing.
Dry, hot and windy conditions make it easier for a fire to burn. This is because fuel is easier to ignite when it's dry and the radiant heat from a fire makes it easy for flames to reach more unburnt fuel.
As fire spreads, it burns pieces of leaves, twigs and bark (embers) that the wind blows in front of the main fire. These embers can travel many kilometres downwind of the fire, igniting new spot fires.
When a bushfire spreads uphill, it moves faster because there is less space between the flames and new fuel to burn. The fire can also burn faster uphill because the radiant heat caused by the fire pre-heats the fuel, making it even more flammable.
The fire's speed and direction of advance also depend on the terrain and the size of the underlying ground. A steep slope will increase the rate of a fire's movement uphill, while flat ground will slow it down. A change in the air currents or wind can also have an impact on the progress of a bushfire, especially if there's a sudden change in the weather.
Why do they burn?
Wildfires are fueled by different types of weather and dry underbrush. They burn quickly and take over the land they're on in just a few minutes, leaving nothing behind but fire-scorched ground and smoke.
Climate change is a major factor in why fires are so dangerous, especially in areas where droughts and warm temperatures are increasing their severity. As the Earth heats up, it's causing forests to remain dry longer, which is making them prime fuel sources for blazes.
High temperatures and low humidity also help fires spread. As hot air rises, it preheats fuel materials that are farther uphill from the fire. That means a small, flashy fuel such as a twig might ignite much faster than a larger log.
Moreover, the fire itself can create its own wind patterns, called fire whirls. They are like tornadoes, but more violent and can hurl flaming logs over long distances.
These wildfires can cause massive damage to a landscape, destroying trees, plants, wildlife and other ecosystems along the way. They also release large amounts of carbon dioxide into the atmosphere, which contributes to climate change.
A wildfire can also destroy homes and property, causing massive losses in lives and incomes for those who live there. It also can cause health problems for those who breathe the smoke and ash that are released into the air after a wildfire occurs.
The most common cause of wildfires is lightning, though other factors can play a role. For example, a fallen power line can cause sparks.
Another factor that contributes to the intensity of a fire is topographical features such as slopes, elevation and aspect. If a fire is burning on the bottom of a steep hill, for example, it will spread more quickly uphill because hot air rising from below the fire can preheat fuels further uphill and cause them to burn more readily.
How do they get started?
The weather plays a big part in how wildfires get started, and it's usually the combination of low rainfall causing a drought, searing hot temperatures, and strong winds that set the stage for a wildfire. Certain cyclical weather patterns like La Nina in the Pacific Northwest or Santa Ana in California can also fan and spread wildfires faster.
One of the most common ways to start a wildfire is to throw cigarette butts out a car window. This causes small embers to blow from the smoke and onto dead vegetation, igniting a fire.
A few other things can spark a wildfire too, including lightning strikes and human-made ignitions, like from equipment or overhead power lines. These ignitions are typically closer to settlements, which makes it easier for emergency responders to spot and extinguish them before they get out of control.
The size of the fuels around a fire can also affect how easy or difficult it is to ignite them and how fast they spread and burn out. Heavy fuels, such as logs, stumps, tree branches, and deep duff (the topsoil or partly decayed leaves and tree needles found under dense stands of brush or trees) take longer to ignite, spread slower, burn out for a longer time, and throw off large volumes of heat when dry.
Other fuels can include dry grass, dead leaves and tree needles, brush, and smaller trees. The ease of ignition and rate of burning are also affected by how much moisture is in these fuels.
When it's warm and dry, wildfires often start in the afternoon when temperatures are highest. That's when the sticks, limbs and other fuels on the ground get very hot from the sun then dry out. Flames are more likely to start uphill because the fuels will be warmer and more readily available for burning as the fire approaches.
What are the risks?
Wildfires in Australia are a natural part of the country's climatic cycle, but they can be extremely destructive. They can destroy crops, livestock, and other important resources, as well as homes and infrastructure. They can also exacerbate air pollution, which is associated with reduced human health and wellbeing.
Fires in Australia are caused by a combination of dry fuel and an ignition source (usually lightning or human activity). The speed at which they spread and the intensity at which they burn depend on wind speed, ambient temperatures, slope angle, and the amount of fuel.
A key concern is that bushfires can spread across regions and become more difficult to control, even with current wildfire management strategies. This can cause unprecedented large-scale impacts, requiring a systems-based approach to address this risk.
Many areas of Australia experience high-frequency fires and some are more likely to be affected than others (figure 1). For example, many regions of the country with flat terrain have been almost completely deforested for agriculture, which reduces the load of vegetation that could be used as fuel during a fire.
This may make them more susceptible to wildfires, especially in dry years when the fuel load is higher. In addition, many areas of Australia experience more frequent droughts than normal, which can increase the likelihood that wildfires will occur during wet periods and be more widespread.
As climate change accelerates, fires in Australia are expected to become more common and burn hotter than ever before. This will result in extensive smoke that can negatively affect human health and wellbeing, as well as ecosystems and wildlife. The impact of smoke can be particularly severe in areas where people live near bushfires and are exposed to the smoke for extended periods.
What can we do to prevent them?
Wildfires are one of the world’s most devastating and expensive natural disasters. They rage in places as diverse as Alaska, Australia, California, Europe and Russia, taking hundreds of lives and leaving thousands of homes and businesses ruined or destroyed.
They also contaminate the air and water with ash and smoke, affecting human health. Doctors have linked wildfire air pollution to increased hospital admissions for elderly patients, asthmatics and other people with respiratory problems.
But there are ways to prevent these fires before they even start. These include reducing the amount of grass, weeds and scrub on your property. It is also important to remove trees and brush that are too close to your home, as well as grazing animals that can be dangerous.
Using technology is another way to prevent bushfires. CSIRO has developed tools that help predict how a blaze will spread and how it could affect buildings, allowing authorities to better prepare fire-fighting resources.
A second project, on Integrated Urban Planning for Natural Hazard Mitigation, is looking at how social media-based'shared responsibility' can be used to improve the resilience of Australian cities to bushfires. CSIRO is also working with universities, local government, and industry to identify how to best support a more integrated approach to managing the risk of bushfires in Australia.
Indigenous knowledge, which has been practiced for thousands of years, has also shown that cultural burns, which aim to create breaks in the forest by burning down old and dead wood, can be effective at reducing fuel loads. A group of Indigenous people living 250 miles north of Sydney, for example, partnered with researchers and showed that cultural burning reduced flammable vegetation by the same amount as wildfires or prescribed fires.
