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You are here Definition of combined disasters

Many populated areas are affected by a wide variety of disasters, such as earthquakes, landslides, tsunamis, flooding, volcanic eruptions, heavy rains, wildfires, etc. Many analyses of disasters take a single-mode approach, which treats disasters as being separate and independent. In many cases, however, the temporal and spatial distributions of these disasters overlap and there can exist interaction relationships between disaster types.

A combined disaster could be defined as a temporal and spatial coincidence of two or more at least medium-scale independent disasters whose consequences do not change in time, resulting in an impact greater than what we would obtain by considering separately the impacts of each disaster independently and summing these up 1. Figure provides a pictorial representation for simultaneous occurring disasters.

Figure – Representation of simultaneous occurring disasters

A combined disaster could also be defined as the consecutive occurrence of one at least medium-scale disaster triggering one or more secondary disasters, thus forming a chain reaction (cascade/domino effect), which acts synergistically, and results in a greater catastrophe than what would be expected by a single-mode disaster. In such case we consider the status of the disaster to change in time.

In the evaluation of the aftermath of a combined disaster the approach should be differentiated between a situation where a primary disaster triggers secondary disaster(s) (e.g. a flood triggering a landslide) and a situation where that primary disaster increases the possibility of secondary disasters occurring. The occurrence of a given disaster may not only cause additional events via cascade or domino effects, such as earthquakes triggering tsunamis, or volcanic eruptions triggering earthquakes, but the initial event may also increase the vulnerability of the region to disasters in the future. An example of this would be a case of an earthquake, which would damage a flood defense structure like a dam.

There is also a direct relationship between the intensity or magnitude of the primary disaster and the intensity of the secondary disaster(s) which may amplify the total impact.

Table summarizes qualitatively the main characteristics of combined disasters, as these pertain to the aforementioned definitions for the purposes of this report.

Table – Combined disaster characteristics
Main characteristicsDisaster modeOccurenceScale of single disasterDisaster status

Simultaneously occurring




Does not change




Changes with time

Table provides a summary of major combined disasters, which occurred in the 2005-2013 period with their respective impacts.

Table – Combined disasters and respective impacts worldwide (2005-2013)
YearDisaster NameIntensity (Richter)Death Toll (persons approx.)Affected Area (103km2)Economic Losses (billion $)


Hurricane Katrina in USA


1,836 pers. dead




Flood in Thailand


815 pers. dead




East Japan earthquake and tsunami


15,870 pers. dead

2,814 pers. missing



  • 1. MATRIX results II and Reference Report/Deliverable D8.5- New Multi-Hazard and Multi-Risk Assessment Methods for Europe - Risk governance and the communication process from science to policy: Evaluating perceptions of stakeholders from practice in multi-hazard and multi-risk decision support models - N. Komendantova, R. Mrzyglocki, A. Mignan, B. Khazai, F. Wenzel, A. Patt, K. Fleming (http://matrix.gpi.kit.edu/downloads/MATRIX-D8.5.pdf)
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