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close this bookAn Overview of Disaster Management (Department of Humanitarian Affairs/United Nations Disaster Relief Office - United Nations Development Programme , 1992, 136 p.)
close this folderChapter 4. Natural hazards
close this folderCharacteristics of particular hazards and disasters 1
View the document(introduction...)
View the documentEarthquakes
View the documentTsunamis
View the documentVolcanoes
View the documentLandslides
View the documentTropical cyclones
View the documentFloods
View the documentDroughts
View the documentEnvironmental pollution
View the documentDeforestation
View the documentDesertification
View the documentPest infestations
View the documentEpidemics
View the documentChemical and industrial accidents

Tropical cyclones

Causal phenomena

Mixture of heat and moisture forms a low pressure center over oceans in tropical latitudes where water temperatures are over 26 degrees C.
Wind currents spin and organize around deepening low pressure over accelerating toward the center and moving along track pushed by trade winds
Depression becomes a tropical cyclone when winds reach gale force or 117 km per hour

General characteristics

When the cyclone strikes land, high winds, exceptional rainfall and storm surges cause damage with secondary flooding and landslides.


Tropical cyclones can be tracked from their development but accurate landfall forecasts are usually possible only a few hours before as unpredictable changes in course can occur.

Factors contributing to vulnerability

Settlements located in low lying coastal areas (direct impact)
Settlements in adjacent areas (heavy rains, floods)
Poor communications or warning systems
Lightweight structures, older construction, poor quality masonry
Infrastructural elements, fishing boats and maritime industries

Typical adverse effects

Physical damage - Structures lost and damaged by wind force, flooding, storm surge and landslides.
Casualties and public health - May be caused by flying debris, or flooding. Contamination of water supplies may lead to viral outbreaks and malaria.
Water supplies - Ground water may be contaminated by flood waters.
Crops and food supplies - High winds and rains can ruin standing crops, tree plantations and food stocks.
Communications and logistics - Severe disruption is possible as wind brings down telephone lines, antennas and satellite disks. Transport may be curtailed.

Possible risk reduction measures

Risk assessment and hazard mapping
Land use control and flood plain management
Reduction of structural vulnerability
Improvement of vegetation cover

Specific preparedness measures

Public warning systems
Evacuation plans
Training and community participation

Typical post-disaster needs

Evacuation and emergency shelter; search and rescue; medical assistance; water purification; reestablish logistical and communication networks; disaster assessment; provision of seeds for planting.

Impact assessment tools

Damage assessment forms, aerial surveys