What is a wildfire?
At their simplest, a wildfire is defined as any uncontrolled vegetation fire where a decision or action is needed about its suppression. Different typologies of wildfire are available in box three below.
Ground fires are fuelled by subterranean roots, duff, and other buried organic matter. They usually burn by smouldering, and can burn slowly for days to months.
Surface fires are fuelled by low-lying vegetation like as leaves, timber or branches, grass, or shrubbery.
Crown fires occur less frequently, during hot and dry summers, but are the most dangerous. They spread from surface fires, with ladder fuels, including tall shrubs, low tree canopies, standing deadwood and trees in poor health, and leaning windblown trees increase the risk of canopy fires.
In practice, these types of fire intermix, and one can develop into another.
Wildfires can spread rapidly, and in the UK, the risk to life and home exists in three main forms.
- Direct flame. Direct flames can be spread quickly by high winds and can directly affect homes and communities.
- Embers. Embers can be spread beyond the frontier of direct flames and cover significant distances. When they are blown close to homes, they can ignite if they land in the wrong place, such as in garden vegetation or leaves stuck in gutters. When they do, they can ignite the whole structure.
- Smoke. Wildfire smoke contains hazardous pollutants, such as nitrogen oxides and fine particulates. Smoke is particularly harmful to vulnerable groups, such as children, pregnant women, older adults, and those with pre-existing health conditions.
How are wildfires caused?
The causes and consequences of wildfires are complex, depending on multiple factors such as prevailing weather and wind conditions, the source of ignition, and the location.
However, the main causes of wildfires are often due to human activity. This can include:
- Unattended fires. Fires that are lit by people include bonfires, campfires, and barbecues. If they are left unattended or not extinguished properly, they can quickly spread and cause nearby wood, vegetation, leaf, or brush clutter to ignite.
- Deliberate fire setting. The deliberate setting of fires can quickly spread out of control.
- Burning waste in gardens or on open land. In hot or dry conditions, even small fires in gardens can spread quickly.
- Burning. Although restrictions and regulations are in place, burning is a common practice among landowners. Done safely by a competent landowner, it is not a problem, but if practiced unsafely can cause a wildfire in hot or dry conditions.
Wildfires can start at any time of year, but are a greater risk in periods of prolonged hot, dry weather, especially when humidity is low. This not only creates the ideal conditions for wildfires starting, but also dries out ignitable materials like vegetation or woodlands, making them more likely to catch fire. Strong winds can also be an exacerbating factor, causing wildfire to spread quickly.
