What Do We Mean by Disaster?

Disaster Definition

Definitions of disaster have been offered from multiple sources: 

A disaster is an occurrence that causes damage, ecological disruption, loss of human life, deterioration of health and health services on a scale sufficient to warrant an extraordinary response from outside the affected community area (World Health Organization, 1998). 

Any event, typically occurring suddenly, that causes damage, ecological disruption, loss of human life, deterioration of health and health services and which exceeds the capacity of the affected community on a scale sufficient to require outside assistance (Landesman, 2004). 

A disaster is characterized as an encounter between forces of harm and a human population in harm’s way, influenced by the ecological context, in which demands exceed the coping capacity of the affected community (Shultz, et al., 2003, 2006a,b, 2007). 

Drawing from these definitions, disasters possess the following common characteristics: 

1)  Extraordinary magnitude of harm

2)  Ecological disruption

3)  Disproportionate impact on vulnerable communities

4)  Demands for response that exceed the community’s ability to cope

5)  Necessity for outside assistance 

Physical damage and destruction are hallmarks of many disasters, but not all.  Disease pandemics, bioterrorism, cyberterrorism, and some incidents involving the release of a hazardous chemical or radiation may create notable disaster events without damage to physical structures.  


The Demand/Capacity Equation

One salient element common to each of the preceding disaster definitions is the imbalance between the demands of the disaster event and the capacities of the affected community to respond.  This has led disaster experts to propose a hierarchy of terms to describe critical incidents:  emergency, disaster, and catastrophe (Quarantelli, 2006).  To this list, we add the term “crisis”:



Capacity exceeds demand and local assets capably handle the demand


Capacity is challenged by demand, but local assets are able to manage the demand


Demand exceeds capacity, necessitating a call for outside assistance


Demand overwhelms and destroys local capacity, creating near-total dependence on outside response


Disaster Classification

Natural disasters.  The Centre for Research on the Epidemiology of Disasters (CRED), located in Brussels , Belgium , maintains the official international disaster registry.  Whenever a disaster occurs anywhere in the globe, the event is reported to CRED and logged into the disaster database.  CRED classifies natural disasters (“acts of nature”) into four subcategories: hydro-meteorological, geophysical, droughts and related disasters, and pandemics.

Hydro-meteorological disasters  include weather-related events such as tropical cyclones (hurricanes, typhoons, cyclones), windstorms, winter storms, tornadoes and floods.
Geophysical disasters  are seismic events related to the motion of the earth’s tectonic plates.  Prominent among geophysical events are earthquakes, tsunamis and volcanoes. 

Droughts  are grouped with additional events including extreme hot and cold temperatures, wildfires, forest fires and insect infestations. 

Pandemic diseases  are distinguished by the global spread of newly-emerging infectious diseases or uncharacteristically virulent strains of well-known foes such as influenza.

Human-generated disasters subsume various forms of “technological” disasters.  Failures of human technologies are rarely intentional.  However, poor judgment or human neglect may be precipitating or contributory factors.  CRED classifies human-generated events into transportation, industrial, or miscellaneous accidents and ecological/environmental events. 

We further subdivide human-generated disasters into non-intentional and intentional events (Shultz et al., 2006; 2007a,b).  Intentional acts of “mass violence” routinely occur as an outcome of acts of terrorism, declared war, civil strife and ethnic conflict; and may also eventuate from mass gatherings and demonstrations. 

Complex emergencies and global catastrophes.  Some disasters defy facile classification into the categories presented above based on their scope, duration and capacity for producing humanitarian crises or threats to global security and survival on a grand scale.  Complex emergencies are multi-dimensional events of long duration, frequently spawned by intentional, human-generated events such as war and civil strife.  According to the World Health Organization and United Nations, a complex emergency is “a humanitarian crisis in a country, region or society where there is considerable breakdown of authority resulting from internal or external conflict which requires an international response that goes beyond the mandate or capacity of any single agency…complex emergencies are typically characterized by: Excessive violence and loss of life; massive displacements of people; widespread damage to societies and economies; the need for large-scale, multifaceted humanitarian assistance; the hindrance or prevention of humanitarian assistance by political and military constraints, and considerable security risks for humanitarian relief workers in some areas,” (UNDP, 2004).  Global catastrophes endanger persons throughout the world and include scenarios such as precipitous global warming, global economic market collapse or massive planetary collision as well as extreme forms of events classified elsewhere such as a nuclear world war or highly virulent pandemic influenza.






Hydrometeorological Disasters

Transportation/vehicle accidents

      Floods and related disasters







Structural collapse



          Tropical cyclones (hurricanes,
cyclones, typhoons, tropical storms)






           Winter storms


Geophysical Disasters

Structure fire



      Volcanic eruptions

Hazardous materials release/spill

      Tsunamis/tidal waves


Droughts and Related Disasters


      Extreme heat


      Extreme cold

Biological agent


Ecological/environmental destruction

      Forest fires

Miscellaneous accidents



Pandemic Diseases


      Newly emerging infectious diseases

Race/ethnic conflict

      High-mortality known infectious diseases

Violent mass gatherings



Biological terrorism: aerosol anthrax

Biological terrorism: smallpox

Biological terrorism: pneumonic plague

Biological terrorism: food contamination


Chemical terrorism: blister agent

Declared war

Chemical terrorism: nerve agent

Civil war

Chemical terrorism: chlorine gas


Chemical terrorism: toxic industrial chemical

Ethnic cleansing/ethnic conflict

Nuclear terrorism: improvised nuclear device

Refugee crisis

Nuclear terrorism: radiological dispersal
device (“dirty bomb”)

Internally displaced persons crisis

Conventional terrorism: improvised
explosive device

Global catastrophes

Cyber terrorism

Source: Shultz et al., 2007a,b

Photo courtesy of FEMA/Barry Bahler