Forest fire risk assessment and cartography - a methodological approach.

Forest fires is part of the ecosystem, but it becomes a risk when by its frequency or its intensity, it destroys the forest beyond what is admitted and threatens men and their activities. Forest fire risk has increased during the 20th century with the socio-economical change of our society (situation in the south of France, but available also in the Mediterranean basin). The evolution of landuse and the decrease of agricultural activity led to more forest fuel and to the multiplication of urban areas in contact with natural forest areas. These wildland/urban interfaces are all the more vulnerable to fire than man is responsible for fire departures. It becomes necessary to manage these areas with prevention devices. However, any prevention policy is initially based on risk assessment and mapping that requires to produce knowledge on the phenomenon and its damaging consequences. But the study and analysis of risk (particularly in the field of forest fires) include difficulties linked to the complexity of the phenomenon. To identify and localize the hazard, various methods can be implemented. Those vary according to the aims, the means and the various forms of modeling used. The methods taken into account in this paper deal with long-term hazard assessment at various scales in opposition with daily hazard estimation for operational purpose. At the present time different methods are available. The studies conducted on these topics are up to date and diverse, for example: comparative study of the risk levels in the administrative units of the European Union states, study of the fire hazard in a district (for a legal purpose), study of ignition hazard along roads in order to complete the preventive maintenance. This diversity shows a wide variety of needs. The difficulties to know the risk and the diversity of the needs led us to study and clarify hazard assessment. The objective of the study , presented in this paper, is to clarify the concepts relating to the risk, to appreciate the multiplicity of the existing needs, to analyze the means of risk evaluation and to identify the data currently usable, as well as the processing and the information systems available. Two steps have been developed: a state of the art and a methodological proceeding.