Natural hazards are hazards attributed to natural phenomena, which can imply a significant threat to people, infrastructure, economic assets and the environment and result in a disaster.
The magnitude of a disaster is not entirely due to natural phenomena as human activity can aggravate or mitigate risks through, for example, the level of consideration to where and how settlements are built, or how natural resources are exploited. Disasters are, therefore, complex events and the problem of disaster prevention and mitigation has many facets.
Natural hazards are usually classified based on their causes and are thus subdivided in “Geological hazards” and “Hydro-Meteorological hazards” and “Biological hazards”.
Geological hazards are caused by earth processes either internal (volcanic eruptions and earthquakes) or external (landslides). Tsunamis can be included among them as they are most often triggered by undersea earthquakes; Tsunamis may also be generated by other events.
Hydro-Meteorological hazards are most often weather-related phenomena (such as floods, droughts/desertification landscape fires, avalanches, hurricanes/storm surges and sea level rise).
Biological hazards are hazards attributed to biological substances that poses a threat to the health of living organisms, primarily humans. This could include a sample of a microorganism, virus, medical waste or toxin that can adversely affect human health. Biohazards could also be harmful to other animals.
It is important to underline that a type of natural hazard can trigger another natural hazard (e.g. a storm can trigger floods, an earthquake can trigger tsunamis and landslides, a volcanic eruption can cause wild fires) or even a technological accident (e.g a tsunami can cause a nuclear accident, a dam failure can cause floods).
Modern technologies provide people with many commodities but entail additional risk from hazardous materials or technologies such as radioactive or toxic substances. Hazardous substances are present mainly in industrial facilities and during transportation.
Accidents caused by fires, explosions or leakages can result in the release of these substances and harm human health, property and the environment. Human exposure to hazardous substances can cause injury or even death for a large number of people.
Accidents such as Bhopal in 1984, Chernobyl in 1986 or Fukushima in 2011 demonstrate the high risk of hazardous materials released into environment. Chemical, radiological (nuclear) accidents or dam failure are a result of human activity and can generate a man-made or technological disaster. There are other types of man-made disasters, related to the failure of public buildings or any interruption or loss of a utility service (power source, life support system, information system or equipment needed to keep businesses running). Chemical or radiological disasters or dam failure could affect millions of people within a radius of many kilometres, and that is why they are the main subjects of our risk review.