What is a Wildfire?

what is a wildfire graphic with wildfire burning in the background

In this article


Types of Wildfires

Wildfire Definitions

How do Wildfires Start?

Why are Wildfires so Dangerous?



The National Geographic defines wildfires as uncontrolled fires that burn in wildland vegetation, often in rural areas. They can burn in forests, grasslands and other ecosystems and have been a part of life on Earth for hundreds of millions of years.

Wildfires consume natural fuels and their spread is often affected by environmental factors such as wind speeds and topography. Though there are wildfire hotspots, they are not a phenomenon specific to a particular region or climate and they’re a significant environmental, societal and economic problem that’s only getting worse.

Though these fires can be started naturally as a result of occurrences like lightning strikes, up to 85% of wildfires are caused by humans. A small portion of rural fires are controlled or prescribed burns and these can sometimes be beneficial. However, the fact remains that the vast majority of wildfires are both human-caused and catastrophically ruinous.

graphic stating that 84% of wildfires in in the united states are caused by humans

In places like California and Australia, wildfires are an almost annual occurrence. These regions often see hot summers with little rainfall and humidity followed by dry autumns after the end of the wet season. This combination of dry vegetation and low rainfall make these areas prime locations for massive wildfire outbreaks. Climate change is undoubtedly making things worse, with warmer temperatures increasing the frequency and severity of fire outbreaks.

This article will begin by looking at some definitional issues before exploring wildfires in more detail, including how they tend to start and what makes them so dangerous to society.

Types of Wildfires

The three types of wildfire are surface, ground, and crown fire. Surface wildfires burn the upper layer of dead plant material and detritus as well as some or all of the vegetation found in the understory. The understory is the underlying level of vegetation such as seedlings, saplings and understory shrubs.

Surface wildfires move rapidly through an area and can reach speeds of up to fourteen miles-per-hour. However, the soil’s moisture often prevents the ignition of the humus layer, protecting the soil and the organisms within it.

graphic for statistic stating that wildfires can reach speeds that exceed 14 miles per hour

Ground fires can be more damaging since they can consume all or most of the organic cover within an area. These fires are typical occurrences during periods of severe and prolonged drought when the entire organic layer dries. Though slower moving than surface fires, they can burn for weeks or even months and often won’t stop until they’re extinguished or all their fuel sources are exhausted.

Crown fires occur within the crowns of trees themselves and can often spread from tree to tree. They are often started by surface or ground fires reaching wooded areas. As you might expect, these fires occur in forests and are more likely to ignite and spread during periods of drought and low relative humidity. Dense and volatile understories can worsen the spread and intensity of crown fires.

Wildfire Definitions - What’s the Difference Between a Forest Fire, Grass Fire and Bushfire?

Uncontrolled fires can be referred to in many ways. Mentions of wildfires, forest fires, grass fires and bushfires are common, but are there differences between them? Other terms used when referring to wildfires more broadly include brush fire and wildland fire. The picture is often complicated by many agencies and publications using the terms interchangeably.

graphic showing different kinds of wildfires including forest fires, grass fires and bushfires

Where they exist, terminological differences are often related to the type of fuel being burned, and therefore to the where the wildfires are occurring. ‘Wildfires’ is a term often deployed as a catch-all term for the types of fires mentioned below:

Forest fires

Forest fires are large and unpredictable fires that occur in forests, woodlands and shrublands. Forest fires can be categorized into low-intensity fires, moderate-intensity fires or high-intensity fires.

  • Low-intensity fires start and spread slowly with little smoke. They do not normally kill mature trees but may kill saplings and shrubs. Low-intensity fires may be best left to burn out naturally because they may help to maintain the health of the forest. Prescribed fire mimics low-intensity fire and is used as a means to maintain many ecosystems.

  • Moderate-intensity fires produce more smoke and higher temperatures than low-intensity fires. They can kill trees and damage the forest. Trees that survive moderate-intensity fires may be seriously weakened and become more likely to be blown over by high winds.

  • High-intensity fires are the most dangerous and damaging types of forest fires. They produce a lot of smoke and are difficult to control. They kill mature trees and can destroy the whole forest. High-intensity fires can also kill wildlife and nearby animals including livestock and wildlife such as birds, reptiles and amphibians.

Grass fires

Grass fires are fires that develop in grasslands, savannahs and other open areas. They can also occur in agricultural areas and can quickly consume crops such as corn, rice, wheat and barley. They are capable of burning for long periods, especially in areas with high temperatures and low levels of rainfall.

Grass fires can become more dangerous during periods of drought when there is little rainfall. Since grass is a fine fuel, grass fires often burn faster than forest fires or bushfires. Fires that kill grasslands and crops can reduce the amount of food that is available for grazing animals, with severe knock-on effects for the food chain.


Bush fires are wildfires that occur in the bush, which is a term (most commonly used in Australia) for a wild area of land. Bushfires are generally slower moving than other types, but have a higher heat output.

Like forest fires, bushfires can spread very quickly and destroy large areas of land.

How Do Wildfires Start?

Fires can be started by anything that can ignite, including downed power lines or sparks from machinery, campfires or cigarettes. The risks of fires starting and spreading are driven by three main factors - which together make the Fire Triangle:

  • Lots of dry fuel to burn (grass, leaves, branches, and other organic matter)

  • Heat to ignite and burn

  • Oxygen in the air

graphic showing the fuel triangle

When it comes to naturally occurring wildfires, the main culprit is usually lightning strikes, which generate heat and cause fires to ignite. Some areas are particularly prone to these kinds of wildfires, such as Canada’s British Columbia, where lightning strikes are responsible for 60% of wildfires.

The devastating 2020 Bay Area Fire which destroyed 5 million acres of land, over 10,000 structures and killed 33 people was also started by lightning storms.

Research suggests that up to 85% of wildfires in the United States are caused by humans, whether intentionally or unintentionally. Human-induced wildfires in the US tripled the length of the region’s fire seasons between 1992 and 2012, from 46 to 154 days.

The most common causes of wildfires are unattended camp and debris fires, discarded cigarettes, and arson.

Why Are Wildfires So Dangerous?

Wildfires have the potential to cause catastrophic damage to property, livelihoods and human health. According to the United States’ National Oceanic and Atmospheric Administration, between 1980 and 2021 the United States had 20 wildfire events that caused more than $1 billion in damage, with 16 of these having occurred since 2000.

The United States spends billions of dollars every year fighting wildfires. In 2020 alone, it spent $2.6 billion. And the damage wrought it far from purely financial: more than 1,000 firefighters have died fighting wildfires in the US since 1910.

Another startling statistic is that wildfires alone account for 20% of global greenhouse gas emissions. That's more than all the world's transit emissions combined.

Even communities far away from where wildfires rage cannot escape their deleterious effects. Smoke and fumes from wildfires have been directly linked to significant health consequences and societal costs, such as hospital admissions and respiratory-related deaths.

One of the the things that makes wildfires so destructive and frightening is that they can spread very quickly, sometimes travelling at a rate of 14.29 miles per hour or more. It is not a coincidence that 'spread like wildfire' has become an idiom in English-speaking countries. By the time a wildfire starts to rage in earnest, it is often too late to save whatever might be in its path. In addition to their terrifying speeds, wildfires are also notoriously hard to predict.

While the most obvious effect of a wildfire is damage to forests, infrastructure and buildings, wildfires can also affect the climate. Forests are some of the world’s best storers and sequesters of carbon. Whey they burn, countless tonnes of carbon dioxide are immediately released into the atmosphere. This in turn contributes to global warming, creating a vicious cycle of increased fire outbreaks and a warming planet.


Wildfires are fast-moving and unpredictable fires that occur in a variety of rural areas. They can be difficult to accurately monitor because they tend to rage in remote locations. Because they spread so quickly, they can very soon get out of control, becoming dangerous and very difficult to extinguish.

Because of this, innovative solutions that seek to detect wildfires quickly are increasingly being developed. These solutions lean on a range of different technologies, from remote sensing to infrared satellite imagery. Dryad’s own solution is a solar-powered mesh network of AI-embedded sensors that can detect a fire within the first 60 minutes. This means often within the initial smouldering phase, before a wildfire has a chance to get out of hand.

Clearly, prevention is the best cure when it comes to wildfires, and there are many effective precautions to reduce the risk of wildfires igniting in the first place. Public education and awareness campaigns have a vital role to play when it comes to risk mitigation.

But as we've seen, accidents do happen, and sometimes the igniting of wildfires is beyond our control. In these situations, rapid and accurate wildfire detection is vital.

graphic comparing wildfire detection speeds

50 views0 comments

Recent Posts

See All