Reflexions on the basis of legal zoning for recurrent mountain risks
Résumé
Risk zoning for mountain hazards remains generally seen as a normative process resulting from transposition of a scheme elaborated for floods. In its hearth is the centennial hazard, a probabilistic reference difficult to properly define, unsuitable for destructive phenomena and little interpretable in terms of exposure. These shortcomings are sources of misunderstandings and they make questionable shortcuts as well as conservative field practices necessary. This article proposes a paradigm shift. Zoning is seen as a compromise between the losses due to the damaging phenomenon and the restrictions that society imposes to itself. The current scientific knowledge does not allow specifying a complete directive procedure, which is anyway not the responsibility of the technical sphere. However, individual risk mapping by combining the hazard model and the damage potential for different elements at risk and then zoning on the basis of acceptability thresholds integrates the multivariate nature of the hazard, allows consideration of uncertainties and authorizes the traceability of the whole decisional procedure. The choice of the individual risk values to which the zone limits correspond and the display of the residual risk after zoning materialize the chosen social compromise, which enables a re-appropriation of the zoning issue by the society. The proposed formal framework is compatible with a wide range of technical solutions and institutional guidelines. Finally, specific recommendations for practice and for future research are formulated. The paper is illustrated by a case study from the field of snow avalanches, but the purpose is transferable to all recurrent rapid mass movements.
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