The notion of risk provides a means of evaluating the eventuality of a danger or peril, or a break in the balance in the interactions between nature and societies. Risk only exists if human groups and their territorial settlements could potentially be affected by the destruction that would follow upon a catastrophe. The degree of probability of an event implies some consciousness of an existing danger, which distinguishes the risk from the hazard, characterised by its unpredictability.
The notion of risk works on the basis of three key aspects: probability, vulnerability and mastery. The first two concern evaluation, while the third is related to the ability to preserve populations by means of adequate preparation. This objective of limiting, or even mastering, potential damage comes up itself against the measure of the evaluation of risk, which shows in the pair intensity/frequency. The weaker the frequency of a catastrophe and the stronger its intensity, the greater the vulnerability.
Degrees of vulnerability and exposure vary considerably according to the levels of development of societies. This notion of risk is thus highly relative, and depends on the way societies view their fragility in the face of perils. Over the course of time, the perception and reactivity of populations facing natural risks has caused them to move beyond fatalism (‘a stroke of fate’, ‘God’s will’) to a demand for protection. The efficiency of the desired measures depends to a considerable extent on the strength of will of the society to reduce vulnerability through actions of prevention and protection, which can take the form of regulations or action protocols, such as the PPR (‘plans de préventions aux risques ‘) which have existed in France since 1995. The implementation of such procedures involves the application of the precaution principle, along with an acknowledgement that public authorities have a responsibility toward citizens in matters of risk management.
The notion of risk applies not only to natural phenomena; technological risks and sanitary risks (epidemics) represent threats as well. Large industrial concentrations and places where toxic products are stored also expose populations to a number of dangers. The notion of risk is also not exclusively linked to catastrophes, i.e., to sudden or violent events whose occurrence and societal impact are almost simultaneous. Any regular deterioration in the terrestrial environment, or in resources whose development or availability may be postponed for several decades, also belongs to the category of risks.
Inside the oikumene, exposure to major risks (earthquakes, cyclones, volcanism, flooding) concerns most of the world’s population.