Different types of disasters will require different intervention approaches. Disasters in the humanitarian sector are classified into three broad categories.

• Slow on-set emergencies
• Rapid on-set emergencies
• Complex humanitarian emergencies

“Understanding disasters can help reduce the risk of future disasters. Disasters occur when communities coping mechanisms are partially or completely destroyed and therefore people are unable to cope with the effects of natural or man-made hazards thus making them vulnerable to suffering.”

Hazards present potential threats which may be natural (hurricanes or earthquakes) or man-made (industrial accidents, war, civil conflict).

Disasters occur when the poor and vulnerable are unable to cope with a major hazard due to underlying social, economic, environmental or political pressures.

Causes of vulnerability including poverty or social exclusion, force people to live in unsafe locations (i.e. prone to earthquake, landslides or flooding) or in an unsafe manner (i.e. poor housing or wholly reliant on subsistence agriculture)

Hazard + Vulnerability= Disaster

A hazardous situation in a country may turn into a disaster when the affected society cannot cope by using only its own resources. Under the circumstances, when lives and property are at immediate risk, humanitarian organisations may deploy emergency teams. Clusters are activated in the case of large-scale emergencies which exceed the in-country capacity of those agencies and other humanitarian organisations that are active in the area on a routine basis.

Example: Disaster Statistics - Deaths - Rapid and Slow Onset (Yr: 1900 to 1999). See CRED (EM-DAT) statistics: the Centre for Research on the Epidemiology of Disasters: www.cred.be.

Typical disaster cycle

Diagram 2: Typical disaster cycle
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Slow on-set emergencies

In slow onset emergencies, situation “A” below, humanitarian organizations and governments are able to put measures in place to mitigate the effects of the disaster and be better prepared to respond to the disaster when it occurs. This should lead to the disaster having a reduced impact on the affected community. If and when the disaster occurs, the humanitarian sector and governments provide the necessary relief supplies and coordination in a timely manner through use of prepositioned stocks and established coordination mechanism.

Diagram 3: Slow on-set emergencies

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Rapid/Sudden on-set emergencies

In case of a natural or man-made sudden on-set disaster situation “B” in the diagram below applies. There is very little time to prepare and the intervention is very much reactive. Relief activities are initiated by the humanitarian community to respond to the immediate needs while planning and preparing for the longer term requirements is being done.

Natural disasters, also referred to as sudden onset disasters, are emergencies caused by natural, technological and environmental calamities. The actions and activities described below will only relate to natural disasters but the Logistics Cluster will have similar functions in technological and environmental disasters.

Sudden on-set/natural disasters are increasing in terms of frequency, complexity, scope and destructive capacity.  During the past two decades, natural disasters have killed millions of people, adversely affected the life of at least one billion more people and resulted in enormous economic damage.  Natural disasters include earthquakes, wind-storms, tsunamis, floods, landslides, volcanic eruptions, wildfires, etc.

The risk of natural disasters is increasing because of population growth, urbanization, and alteration disruption of the natural environment, substandard dwellings and public buildings and inadequate infrastructure maintenance.

Diagram 4: Rapid on-set emergencies

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Complex humanitarian emergencies

Complex emergencies are defined by the Inter-Agency Standing Committee (IASC) as, “a humanitarian crisis in a country, region or society where there is total or considerable breakdown of authority resulting from internal or external conflict and which requires an international response that goes beyond the mandate or capacity of any single and/or ongoing UN country programme.”

Likely characteristics of a complex emergency include:

• a large number of civilian victims, populations who are besieged or displaced, human suffering on a major scale;
• substantial international assistance is often needed and the response goes beyond the mandate or capacity of any one agency;
• delivery of humanitarian assistance is often impeded or prevented by parties to the conflict;
• high security risks for relief workers providing humanitarian assistance; and
  
• increasingly relief workers are being targeted by parties to the conflict.

Disaster risk relates to the chance of negative consequences when a particular hazard affects vulnerable people or locations. Risks can be reduced through measures that mitigate the effects of disaster:

• Structural measures (i.e. design of buildings, physical barriers);
• Non structural measures such as environmental control or land use regulation, training and public awareness.

And measures that prepare for disasters i.e.:

• planning and early warning systems;
• stockpiling and increased community response capacity;
• coordination between actors at national, international and global level; and
  
• logistics capacity assessment and mapping of existing logistics resources.

See Stock Prepositioning topic.