Mapping wildland-urban interfaces at large scales integrating housing density and vegetation aggregation for fire prevention in the South of France

Every year, more than 50,000 wildland fires affect about 500,000 ha of vegetation in southern European countries, particularly in wildland-urban interfaces (WUI). This paper presents a method to characterize and map WUIs at large scales and over large areas for wildland fire prevention in the South of France. Based on the combination of four types of building configuration and three classes of vegetation structure, 12 interface types were classified. Through spatial analysis, fire ignition density and burned area ratio were linked with the different types of WUI. Among WUI types, isolated WUIs with the lowest housing density represent the highest level of fire risk

Land cover analysis in wildland-urban interfaces according to wildfire risk: a case study in the South of France

Each year, forest fires destroy about 500,000 ha of vegetation in Europe, predominantly in the Mediterranean region. Many large fires are linked to the land transformations that have taken place in the Mediterranean region in recent decades that have increased the risk of forest fires. On the one hand, agricultural fallows and orchards are slowly being colonized by vegetation, and on the other hand, the forest is not sufficiently used, both of which result in increased accumulation of fuel. In addition, urbanization combined with forest extension results in new spatial configurations called wildland-urban interfaces (WUI). WUI are commonly defined as areas where urban areas meet and interact with rural lands, wildland vegetation and forests. Spatial analyses were performed using a WUI typology based on two intertwined elements, the spatial organization of homes and the structure of fuel vegetation. The organisation of the land cover in terms of representativeness, complexity or road density was evaluated for each type of WUI. Results showed that there were significant differences between the types of WUI in the study area. Three indicators (i) fire ignition density, derived from the distribution of fire ignition points, (ii) wildfire density, derived from the distribution of wildfire area and (iii) burned area ratio, derived from the proportion of the burned area to the total study area were then compared with each type of WUI. Assuming that the three indicators correspond to important aspects of fire risk, we showed that, at least in the south of France, WUI are at high risk of wildfire, and that of the different types of wildland-urban interfaces, isolated and scattered WUI were the most at risk. Their main land cover characteristics, i.e. low housing and road densities but a high density of country roads, and the availability of burnable vegetation such as forested stands and shrubland (garrigue) explain the high fire risk. Improving our knowledge of relationships between WUI environments and fire risk should increase the efficiency of wildfire prevention: to this end, suitable prevention actions and communication campaigns targeting the types of WUI at the highest risk are recommended

Evaluation et cartographie du risque d'incendie de forêt à l'aide d'un SIG. Exemple d'un massif forestier du sud de la France.

Les différentes composantes de l'aléa feu de forêt sont des données géographiques, référencées spécialement et qui peuvent être introduites et superposées dans le SIG. Chaque facteur (ou combinaison de facteurs) a été cartographié et intégré sous forme numérique dans le SIG, puis traduit en terme de risque

Characterization and mapping of dwelling types for forest fire prevention

Définition des habitats isolés, diffus et groupés. Méthode de caractérisation et de cartographie de ces types d'habitat dans le contexte de prévention du risque d'incendie. Mise en relation des types d'habitat avec le risque d'incendie. / In a context of forest fire risk , the development of actions concerning wildfire prevention and land management is necessary and essential particularly in wildland urban interfaces (WUI). The term WUI' always includes components such as human presence and wildland vegetation. Both the hazard (probability of fire outbreak, distribution) and the vulnerability of urban areas can be characterized through the spatial organization of houses and vegetation. The first required step is to characterize and map WUI in large areas and at a large scale, which in turn requires qualifying different types of dwellings and mapping them. With this goal in view, the paper presents a brief synthesis of results coming from an exploratory process for the characterization of dwelling types (Lampin et al., 2007), and develops a method based on GIS-geo treatments to characterize different types of dwelling with regard to fire risk. Three types of dwellings were classified: isolated dwellings, scattered dwellings and clustered dwellings, using criteria based on the distance between houses, the size of clusters of houses and housing density, which can be mapped automatically. Within dwelling types, the density value of forest fire ignition changed and was twice as high for isolated dwellings as for clustered dwellings. The spatial organization of dwellings seems to have a real impact on fire occurrence. Thus maps of different dwelling types can be interpreted for use in developing fire fighting strategies or prevention actions concerning end-users such as forest and land planning managers or fire-fighters

Et si l'efficacité de la lutte contre les incendies jouait comme une incitation aux comportements les plus risqués ?

L'efficacité de la lutte contre les incendies de forêt est-elle susceptible de faire oublier la forte relation qui existe entre construction en forêt et risque ? C'est le paradoxe dont nous fait part cet article. Il nous apporte aussi des données objectives sur un vieux débat : pourquoi et comment responsabiliser les candidats à l'installation dans une zone à risque ? Débat cependant toujours d'actualité, sachant que, face au développement de l'urbanisation, les moyens publics ne pourront pas assumer la protection de toutes les habitations

Mise au point d'une typologie de combustibles pour la Basse Provence calcaire

La typologie du combustible est un outil utilisé par les gestionnaires des milieux naturels soumis aux incendies dans de nombreux pays et massifs subissant ce risque. Cet outil permet d'intégrer le comportement du feu dans la gestion des milieux et dans la planification, à l'échelle d'un massif forestier. Ces typologies caractérisent la répartition verticale et horizontale de la végétation, ainsi que sa biomasse, éléments déterminants du comportement du feu, en milieu naturel. Le Cemagref d'Aix-en Provence, sur la base de près de 150 descriptions de végétation situées en Basse Provence calcaire, a bâti une typologie des structures de végétation et a pu caractériser le comportement du feu, dans chacun des onze types de combustibles construits

Amélioration de la connaissance des causes d'incendie de forêt et mise en place d'une base de données géoréférencées

Dans le cadre du programme Forest Focus, le Cemagref d'Aix-en-Provence a réalisé un guide technique intitulé « Amélioration de la connaissance des causes de départ de feu de forêt » et l'agence MTDA a développé le prototype d'un module de saisie et de cartographie interactive des incendies de forêt. Cet article présente la méthode d'investigation de recherche des causes de départ de feu adaptée au contexte méditerranéen français ; un encadré concerne spécifiquement le module de saisie et de cartographie interactive permettant d'alimenter une base de données géoréférencées

Wildfire risk associated with different vegetation types within and outside wildland-urban interfaces

Wildland-urban interfaces (WUIs) are areas where urban settlements and wildland vegetation intermingle, making the interaction between human activities and wildlife especially intense. Their relevance is increasing worldwide as they are expanding and are associated with fire risk. The WUI may affect the fire risk associated with the type of vegetation (land cover/land use; LULC), a well-known risk factor, due to differences in the type and intensity of human activities in different LULCs within and outside WUIs. No previous studies analyze this interaction between the effects of the WUI and the LULC, despite its importance for understanding the patterns of fire risk, an essential prerequisite to undertake management decisions that can influence fire regimes. The aim of this study is to assess the effect of the WUI on fire ignition risk and the area burned, and the interaction between its effect and that of the LULC. We used a database of 26,838 wildfires recorded in 2006-2011 in NW Spain and compared fire patterns in relation to WUI and LULC with a random model, using a Montecarlo approach. There was a clear effect of the WUI on the risk of both fire ignition and spread (higher ignition risk but lower risk of spread in WUIs). The risk of fire was also affected by LULC and, interestingly, the pattern among LULCs differed between WUI and non-WUI areas. This interaction WUI x LULC was particularly important for forestry plantations, which showed the highest increase in ignition risk in WUI compared to non-WUI areas. Native forests and agricultural areas had the lowest ignition risk. Agricultural areas showed the smallest difference in fire size between WUI and non-WUI areas, while shrublands showed much larger fires outside WUIs. Deliberate fires were larger in general than those with other causes, especially outside the WUI. The differences found between LULCs in fire risk, both in WUI and non-WUI areas, have interesting implications for fire management. Promotion of land covers with low fire risk should be considered as a low cost alternative to the usual fire prevention measures based on fuel load reduction, which require the continuous clearing of vegetation. In this regard, the low fire risk in native forests should be taken into account. Native forests naturally colonize many areas in the study region and require low or no management, in contrast with agricultural areas, also with low fire risk but requiring continuous management in order to avoid colonization by natural vegetation