Natural hazards
From HFA-PEDIA
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About natural hazards
Natural hazards are natural processes or phenomena occurring in the biosphere that may constitute a damaging event. Natural hazards can be classified by origin namely: geological, hydrometeorological or biological. Hazardous events can vary in magnitude or intensity, frequency, duration, area of extent, speed of onset, spatial dispersion and temporal spacing.
Tropical storms
Source: Reuters; 20-08-2008
"Hurricane", "cyclone" and "typhoon" are different terms for the same thing: a revolving tropical storm accompanied by torrential rain and wind speeds exceeding 119 kilometres per hour (74 miles per hour). The storms can be hundreds of kilometers wide and they bring destructive winds, torrential rain, storm surge and sometimes tornadoes. The worst recent storms include Cyclone Nargis, which hit Myanmar in 2008 leaving nearly 140,000 people dead or missing, and Hurricane Katrina, which destroyed New Orleans in 2005, killing more than 1,800 people and displacing 2.16 million.
In the Americas and Caribbean the tropical storms are called "hurricanes". In the western Pacific, East Asia and Australia they are "typhoons". And in the Indian Ocean they are "cyclones".
The storm strength varies from Category 1 to 5, the lowest referring to storms with winds of 119-153 kph (74-95 mph) and Category 5 to winds exceeding 249 kph (155 mph), according to the Saffir-Simpson Hurricane Scale. The impact of the storm, however, depends not just on wind speed, but also on where they strike, how much flooding they cause and the quality of the buildings and infrastructure.
Weather-watchers use satellite images to track tropical storms as they develop, and try to predict when and where one will hit land and at what speed; but storms are unpredictable and can suddenly weaken or swerve off course.
Wind speeds
- Less than 63 kph (39 mph) - tropical depression
- More than 63 kph - tropical storm and given a name
- More than 119 kph - designated either a hurricane, typhoon, severe tropical cyclone, severe cyclonic storm or tropical cyclone depending where it is in the world
Tornadoes
Some tropical storms bring with them tornadoes - destructive rotating columns of air which form from a storm cloud and reach towards the ground. These twisting spirals of wind can lift houses off foundations. The tornado ranges from just a few meters across to over a kilometer, and can last up to an hour or more. The strongest have winds of over 420 kph (260 mph). Scientists do not know exactly how they are formed, making them hard to predict. The average warning time is 12 minutes.
When do Tropical Storms occur?
The cyclone season in the Pacific/South East Asia region runs from May to November. The Americas/Caribbean hurricane season runs from Jun 1 to Nov 30, peaking in August and September. And the cyclone and typhoon season in East Asia, South Pacific and Australia normally runs from November to April.
In Northern India tropical cyclones usually occur from April to June, and September to November. The East Coast of Africa normally experiences tropical cyclones from November to April.
Geological hazards
Natural earth processes or phenomena that may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation. Geological hazard includes internal earth processes or tectonic origin, such as earthquakes, geological fault activity, tsunamis, volcanic activity and emissions as well as external processes such as mass movements: landslides, rockslides, rock falls or avalanches, surfaces collapses, expansive soils and debris or mud flows. Geological hazards can be single, sequential or combined in their origin and effects.
Hydrometeorological hazards
Natural processes or phenomena of atmospheric, hydrological or oceanographic nature, which may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation.
Hydrometeorological hazards include: floods, debris and mud floods; tropical cyclones, storm surges, thunder/hailstorms, rain and wind storms, blizzards and other severe storms; drought, desertification, wildland fires, temperature extremes, sand or dust storms; permafrost and snow or ice avalanches. Hydrometeorological hazards can be single, sequential or combined in their origin and effects.
Biological hazards
Processes of organic origin or those conveyed by biological vectors, including exposure to pathogenic micro-organisms, toxins and bioactive substances, which may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation.
Examples of biological hazards: outbreaks of epidemic diseases, plant or animal contagion, insect plagues and extensive infestations.
Related pages
Related Internet links
Reuters - AlertNet
