Ruins from the 1906 San Francisco earthquake, remembered as one of the worst disasters in the history of the United States
A disaster is a serious problem occurring over a period of time that causes widespread human, material, economic or environmental loss which exceeds the ability of the affected community or society to cope using its own resources. Disasters are routinely divided into either "natural disasters" caused by natural hazards or "human-instigated disasters" caused from anthropogenic hazards. However, in modern times, the divide between natural, human-made and human-accelerated disasters is difficult to draw.
Examples of natural hazards include avalanches, flooding, cold waves and heat waves, droughts, earthquakes, cyclones, landslides, lightning, tsunamis, volcanic activity, wildfires, and winter precipitation. Examples of anthropogenic hazards include criminality, civil disorder, terrorism, war, industrial hazards, engineering hazards, power outages, fire, hazards caused by transportation, and environmental hazards.
Developing countries suffer the greatest costs when a disaster hits – more than 95% of all deaths caused by hazards occur in developing countries, and losses due to natural hazards are 20 times greater (as a percentage of gross domestic product) in developing countries than in industrialized countries.
The word disaster is derived from Middle French désastre and that from Old Italian disastro, which in turn comes from the Ancient Greek pejorative prefix δυσ- (dus-) "bad" and ἀστήρ (aster), "star". The root of the word disaster ("bad star" in Greek) comes from an astrological sense of a calamity blamed on the position of planets.
Complex disasters, where there is no single root cause, are more common in developing countries. A specific disaster may spawn a secondary disaster that increases the impact. A classic example is an earthquake that causes a tsunami, resulting in coastal flooding, resulting in damage to a nuclear power plant (such as the Fukushima nuclear disaster). Some manufactured disasters have been wrongly ascribed to nature, such as smog and acid rain.
|The sudden, drastic flow of snow down a slope, occurring when either natural triggers, such as loading from new snow or rain, or artificial triggers, such as explosives or backcountry skiers.
|A severe snowstorm characterized by very strong winds and low temperatures
|The shaking of the Earth's crust, caused by underground volcanic forces of breaking and shifting rock beneath the Earth's surface
|Fires that originate in uninhabited areas and which pose the risk to spread to inhabited areas (see also Wildfire § Climate change effects)
|Flash flooding: Small creeks, gullies, dry streambeds, ravines, culverts or even low-lying areas flood quickly (see also Effects of climate change)
|Rain occurring when outside surface temperature is below freezing
|A prolonged period of excessively hot weather relative to the usual weather pattern of an area and relative to normal temperatures for the season (see also Effects of climate change § Heat waves and temperature extremes).
|Geological phenomenon which includes a range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows
|An electrical discharge caused by lightning, typically during thunderstorms
|The sudden eruption of carbon dioxide from deep lake water
|Rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls (see also Tropical cyclones and climate change)
|A series of waves hitting shores strongly, mainly caused by the displacement of a large volume of a body of water, typically an ocean or a large lake, usually caused by earthquakes, volcanic eruptions, underwater explosions, landslides, glacier calvings, meteorite impacts and other disturbances above or below water
|The release of hot magma, volcanic ash and/or gases from a volcano
A natural disaster is the highly harmful impact on a society or community following a natural hazard event. Some examples of natural hazard events include: flooding, drought, earthquake, tropical cyclone, lightning, tsunami, volcanic activity, wildfire. A natural disaster can cause loss of life or damage property, and typically leaves economic damage in its wake. The severity of the damage depends on the affected population's resilience and on the infrastructure available. Scholars have been saying that the term natural disaster is unsuitable and should be abandoned. Instead, the simpler term disaster could be used, while also specifying the category (or type) of hazard. A disaster is a result of a natural or human-made hazard impacting a vulnerable community. It is the combination of the hazard along with exposure of a vulnerable society that results in a disaster.
In modern times, the divide between natural, human-made and human-accelerated disasters is quite difficult to draw. Human choices and activities like architecture, fire, resource management and climate change potentially play a role in causing natural disasters. In fact, the term natural disaster was called a misnomer already in 1976.Natural disasters can be aggravated by inadequate building norms, marginalization of people, inequities, overexploitation of resources, extreme urban sprawl and climate change. The rapid growth of the world's population and its increased concentration often in hazardous environments has escalated both the frequency and severity of disasters. Extreme climates (such as those in the Tropics) and unstable landforms, coupled with deforestation, unplanned growth proliferation and non-engineered constructions create more vulnerable interfaces of populated areas with disaster-prone natural spaces. Developing countries which suffer from chronic natural disasters, often have ineffective communication systems combined with insufficient support for disaster prevention and management.
Human-instigated disasters are the consequence of technological or human hazards. Examples include war, social unrest, stampedes, fires, transport accidents, industrial accidents, conflicts, oil spills, terrorist attacks, and nuclear explosions/nuclear radiation.
One opinion argues that all disasters can be seen as human-made, due to human failure to introduce appropriate emergency management measures.
Famines may be caused locally by drought, flood, fire, or pestilence, but in modern times there is plenty of food globally, and sustained localized shortages are generally due to government mismanagement, violent conflict, or an economic system that does not distribute food where needed.
|The intentional release or dissemination of biological agents as a means of coercion
|A disturbance caused by a group of people that may include sit-ins and other forms of obstructions, riots, sabotage and other forms of crime, and which is intended to be a demonstration to the public and the government, but can escalate into general chaos
|Even with strict building fire codes, people still perish in fires
|Hazardous material spills
|The escape of solids, liquids, or gases that can harm people, other living organisms, property or the environment, from their intended controlled environment such as a container.
|Nuclear and radiation accidents
|An event involving the significant release of radioactivity to the environment or a reactor core meltdown and which leads to major undesirable consequences to people, the environment, or the facility
|Caused by summer or winter storms, lightning or construction equipment digging in the wrong location
This definition includes indirect losses of life caused after the initial onset of the disaster such as secondary effects of, e.g., cholera or dysentery. This definition is still commonly used but has the limitations of number of deaths, injuries, and damage (in $). UNDRO (1984) defined a disaster in a more qualitative fashion as:
an event, concentrated in time and space, in which a community undergoes severe danger and incurs such losses to its members and physical appurtenances that the social structure is disrupted and the fulfilment of all or some of the essential functions of the society is prevented.
As with other definitions of disaster, this definition not only encompasses the social aspect of disaster impact and stresses potentially caused but also focuses on losses, implying the need for emergency response as an aspect of the disaster. It does not, however, set out quantitative thresholds or scales for damage, death, or injury, respectively.