A wildfire is a nature reserve, such as a forest area, heathland area, dune area or peat area that is on fire. Forest fire is the best-known form of wildfire because it is the most violent and visible.
As with any fire, four conditions must be met for a wildfire to start: an ignition source, a sufficiently high temperature, oxygen and fuel. The presence of water inhibits the temperature rise due to evaporation of the water present and complicates the combustion process.
There is fuel, because there is a lot of combustible material in the form of trees and/or shrubs. Moreover, if it has not rained for a long time, the fuel can catch fire very easily. There are often rotting branches and low shrubbery on the ground, all of which are also highly combustible.
Even in the ground there is often sufficient fuel and oxygen to allow a forest fire to move underground, although this will be less violent than an above-ground fire.
There is oxygen, because the fuel is not all packed together, but leaves enough room for the supply of oxygen. Even more oxygen is available when the fire is fanned by strong winds, such as the mistral in southern France.
When a forest fire is sufficiently intense, the oxygen supply can be further enhanced because the hot combustion gases rise and colder, oxygen-rich air can be drawn in from the environment. In a large wildfire, the wind generated by this effect is of gale force.
A sufficiently high temperature
A sufficiently high temperature can be easily guaranteed by the scale of a wildfire and the energy released during the fire itself.
In a violent forest fire, the radiant heat from the fire tens of meters away is enough to ignite new trees. In this way, a fire can cross large trenches made to contain the fire.
Origin of a forest fire
A forest fire can start if a high temperature occurs locally; enough to start a fire. This is possible when:
a fire is deliberately started (arson or shifting farming by chopping and burning).
Careless handling of fire (barbecue or cigarette)
lightning strike occurs
a concentration of sunlight is created by lens action (in, for example, a discarded glass bottle).
showers of sparks from frictional contact between train wheels and railway tracks while blocking the rotational movement that can ignite roadside vegetation.
hot parts from or from the exhaust of, for example, a chainsaw, or a vehicle with a combustion engine. Some of these causes are natural: forest fires have existed for as long as there have been forests. When a forest is not disturbed by humans, there will be an equilibrium in which small fires regularly rage that thin the undergrowth and go out on their own without causing major damage to the trees. However, since humans have "helped" the forests by putting out these small fires, larger, unstoppable fires have been growing. This can cause a lot of combustible material to accumulate, which can cause a real conflagration.
A wildfire index is used in various countries to estimate the risks. This index calculates the risk based on a number of data.
Forms of wildfire
Ground fire is a fire in the humus layer on the ground and largely rages underground. The propagation of this type of fire is quite slow, but the fire fighting is very difficult because the seat of the fire is difficult to reach. Ground fire occurs not only in forests but also in heathland areas.
Loop fire is a fire in the lowest vegetation layer in the forest. This concerns the layer of dead or fallen material and grass, thin branches and shrubs low above the ground. Walking fire can occur in ve