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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.

South-eastern France is the most wildfire-prone region of the country. To identify the main driving factors in fire density (defined as the number of fires per hectare) at the local scale (clusters of communities that are homogeneous in terms of land cover, climate and wildland–urban interface (WUI)) and to assess their spatial variation at this scale, fire density was investigated in the département Bouches du Rhône using geo-referenced fire ignitions. To assess relationships between fire density and explanatory factors, statistical analyses and spatial evaluation were performed on each cluster taking into account climatic conditions, topography, land cover, WUI (defined as a buffer of 100 m around housing located less than 200 m from natural vegetation), minor road and population densities, with fire density as the dependent variable. High fire density was mainly related to high proportion of WUI in the study area. The proportion of natural vegetation and steep slope were also among the most important drivers of fire density. Depending on the cluster, some biophysical factors can in turn enhance or mitigate fire density but coolest and wettest climate conditions related to highest elevations as well as low housing density always mitigated fire density. This work showed that, at the local scale, the identification of factors driving fire density could improve fire prevention because this would enable the factors to be better targeted.

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