Forest fire risk in the wildland-urban interface - Elements for the analysis of the vulnerability of municipalities and homes at risk

In many Mediterranean areas, the widespread abandonment of croplands and lost of mosaic
landscape due to the natural forest recolonization during the lasts dacades, is resulting in a new
forest fire risk scenario. This, together with the effects of climate change has contributed to the
emergence of so-called large fires (LF). These types of fires are characterized by extreme and
virulent behaviour, moving at high speed, with large flames and intensity, allowing to burn wide
surfaces in short time. In this situation, regardless of whether the surface covered is large or
small, we are talking about catastrophic and high intensity fires that exceed the suppression
capacity of emergency services.
Parallel to this dynamic expansion of forests, many regions of the Mediterranean have experienced
significant urban development in forest areas or in contact with the forest, either in the form
of housing developments or isolated houses. These areas of contact between the forest and
houses are called wildland-urban interface areas (WUI), and in particular are subject to the
current risk of wildfires. When a large fire approaches an interface area it generates a widespread
emergency due both to the ability of fire to penetrate urban areas and propagate itself throughout
its interior, as well as the problems arising from an environment dominated by smoke such as
lack of visibility, breathing difficulties or high levels of stress and uncertainty on the part of the
population. Examples of these crisis situations are present throughout the Mediterranean basin,
unfortunately sometimes having meant the loss of human lives.
Regarding the ability to access the fire within the interface, the problem is not restricted to only
housing in direct contact with the forest (which are exposed to the impact of the flames), but
also the inside of the housing development is also subject to the fire risk, where fire can spread
through homes and garden elements. This is due to the ability of high intensity fires to issue
sparks, small incandescent plant materials that are transported by the column of smoke tens
and even hundreds of meters away. A rain of sparks can cause new sources of fire far beyond
the main front of the fire. Moreover, the layout between the houses can favour the spread of fire
inside the housing development, by means of flammable elements from buildings and gardens
(furniture, curtains, piles of wood, landscaping vegetation, etc.).
As a result, we are facing a new paradigm where fires not only affect forest stands, but they also
have an impact on housing and people. Consequently, means of suppression have to prioritize
and protect the population and their property from the forest, capitalizing a large number of
resources to achieve this; resources that becomes unavailable to control and suppress the fire
spreading into the forest.
Thus, the challenges to improve the management of wildfire risk and to mitigate the impact of
LFs is focus on acting, on the one hand, on the fire’s ability to spread (related to the amount of
vegetation available to burn) and, on the other hand, reducing the vulnerability of citizenship
and property exposed to the forest fire risk. In this regard, concerning the fire’s ability to spread,
we can intervene by reducing tree density and the amount of vegetation in forest understroy.
To minimize the risk to people and property it is essential to reduce the vulnerability of housing
to be affected by the flames, and know how to act in case of a fire.
Laws are common that govern preventive measures in the souroundings of wildland-urban
interfaces, usually focusing on the creation of a fuel break outside the perimeter of houses
and housing developments where the vegetation is reduced to lessen the intensity of the
fire when impacting the housing. However, less common are specific obligations aimed at
individual property (housing), gardening and exterior construction elements of homes to
reduce the risk of fire. Having tools available that enable and facilitate the evaluation of the
degree of vulnerability in many areas (from the municipal level to private property) within a
locality emplaced in a wildfire risk zone, may facilitate the application of the most appropriate
prevention and protection measures.