More than 50,000 wildland fires in southern Europe affect 500,000 hectares of land every year and kill a number of people. Wildland-urban interfaces (WUIs) are areas where human settlements border or intermingle with undeveloped wildland vegetation as urban development encroaches on rural areas. As 90 per cent of wildland fires are caused by human activities in Mediterranean Europe, WUIs are particularly at risk. In the context of high urban pressure and the accumulation of wildland biomass, they represent serious problems in terms of fire risk management.
The researchers characterised the extent of WUIs over the study area in the south-east of France in order to investigate how the arrangement of human settlements in WUIs affects the risk of fires igniting and their spread. Representing 167,670 hectares, the land cover is 60 per cent forestland (forests and scrubland), 20 per cent urban areas and 20 per cent agricultural land. Over the last 10 years the risk of wildfires in or around WUIs has been high with about 165 fires starting and 200 hectares of surface area burned per year.
Using remote sensing and other sources, the researchers sorted vegetation into three types according to whether it was absent, sparse (with open areas) or dense (vegetation always present). Houses were defined as dwellings occupied permanently, temporarily or seasonally, with a 50m perimeter. The researchers did not include agricultural, industrial, commercial and public buildings (although agricultural practices are a major cause of ignition as well). Houses were classified into four types as: isolated, scattered, dense clustered or very dense clustered houses. A WUI map was therefore built on the 12 types of interfaces.
The map revealed that WUIs in the study area were indeed widespread: about 30 per cent of the study area was classified as WUIs and 56 per cent of the houses were found in these areas. Although the proportion of WUIs with isolated housing represented only 12 per cent of the WUI types, they nevertheless covered a large area, had the highest risk of fire ignition and the greatest proportion of burnt areas.
Recommendations for forest and fire management arising from the study include strengthening the actions required to prevent the spread of fires, such as clearing bushes and pruning trees to break the horizontal and vertical connections of vegetation (creating so-called 'fires breaks'). Generally, the area to be cleared around very densely clustered houses is around 10 times less than around isolated houses in WUIs. This would imply that regular clearing of bushes around isolated houses in the most exposed WUIs is less feasible than for clustered WUIs, as the area to be cleared is typically around 1 hectare.
Further consequences for land management to reduce the level of fire risk in the main WUIs include the suggestion that isolated housing should be avoided and compact urban development encouraged. In addition, more appropriate fire prevention information for the general public is needed to raise awareness and reduce the risk of fires starting.