Geoscience Reference
In-Depth Information
about the confusion that exists between the hazard and what impacts this hazard can
have on human life. For example, flash floods or landslides are not hazards, but are
the result of a combination of a hazard (in this case rainfall) and the susceptibility (a
potential) of the area in which the landslide can take place. If the inhabitant of a
villa or a company manager arrive at their respective properties and find that water
levels have reached their front door, their main worry is to try and find the best
solution to decrease the water level, or flood level, which is perfectly normal. The
water level, or flood level, is referred to here as the hazard. This vision cannot be
the vision of scientists or territorial managers, who have to understand the reasons
why such a problem has occurred in the first place, and to try and find a way so that
the problem does not occur again, or so that it occurs much less frequently without
leading to too many social and economic problems. Therefore, the hazard is the
source of the problem, the triggering factor of an event, which may lead to
dangerous symptoms.
Forest fires, bush fires, or savannah fires only start and develop if certain
conditions take place at the same time: the symptoms that develop (the flames) are
always created in the same way, according to the same steps, and in identifying
these steps, it is then possible to isolate the different components of the risks that are
linked to the creation of a fire. For a flame to be created there needs to be a spark,
however, other factors need to be present for a forest fire to develop. One of the
most important factors is the current weather when the spark is ignited. Forest
regions in wet areas do not experience many fires, on the opposite. Mediterranean
forests or shrub land are both the cause and consequence of forest fires, and this is
due to the summer droughts that occur in this region. Thus, a strong relationship
undoubtedly exists between forest fires and climate. To understand this relationship,
as well as its application (which are used to both understand and forecast such fires),
it is necessary to obtain geographical information.
8.1.2.
The components of forest fires
8.1.2.1.
Hazard
As is the case for other natural risks, forest fires are indirectly linked to local
climate factors or to local weather. However, the different climate factors, as well as
the weather, dictate the way in which forest fires develop.
A forest fire (or fire of any type of vegetation) can be divided into three main
parts, which tend to occur in chronological order. Initially, a flame or spark is
required so that a forest fire can develop. The source of the flame is natural (from a
flash of lightening), or as is the case in the Mediterranean region of France, the
source of the flame tends to be linked to humans, started either accidently or
maliciously. Statistics taken from the Prométhée file
1
[PRO 07] show that the cause
of approximately 50% of all fires is unknown. This figure is much higher in
1 Prométhée is an e-data base platform that exists in France.
