Hazards are low-probability, high-magnitude phenomena that have the potential to cause large negative impacts on people. While this definition is unavoidably imprecise (what counts as a "phenomenon"? what probabilities qualify as "low"? and what impacts qualify as "large" or even "negative"?), in general hazards can be understood as acting outside of daily human expectations to adversely affect the quality of life of those exposed to them. Hazards refer to a prospect or risk of an occurrence; a particular occurrence of a hazard is more typically termed a "disaster" or sometimes an "extreme event"; when they are technological in origin they may be termed "accidents."

The remains of a trailer park in Miami, Florida, destroyed during Hurricane Andrew. Andrew was one of the most destructive hurricanes ever to hit the U.S., raging from August 16 to August 28, 1992. (© Tony Arruza/Corbis.)

Some types of phenomena—such as hurricanes, earthquakes, landslides...