Natural Hazards: Causes and Effects - Disaster Management Center ...

a set of activities in anticipation that a cyclone will strike. When the cyclone is potentially within
24 hours of landfall, a “cyclone watch” is issued. This stage marks the emergency period when
an advanced set of precautions are to be taken, including evacuation from vulnerable
communities.
For many nations, however, the present international system of warning is inadequate. For
example, some of the island nations of the South Pacific are spread out over enormous
distances. The outer islands are without constant radio contact with a potential warning source.
For some people or industries, the 48-hour warning is also inadequate. The fishing industry
may need 72 hours advanced warning for their fisherman and boats to reach safe harbor.
Cement plants may need three to four days to shut down their operations and protect the
equipment.
Evacuation
More than one-half the loss of life from tropical storms is due to drownings, either from the rise
in sea water inundating the land or from floods induced by excessive rainfall. Evacuation has
been a successful means of reducing the loss of life in the United States, as when 300,000
people were evacuated in advance of Hurricane Betsy in 1965. Only 75 lives were lost, despite
damages of over $1.4 billion. Evacuation requires considerable prior planning and coordination
of warning systems and evacuation plans. It has so far proved impracticable in areas like
Bangladesh where communications are poor and local public awareness or motivation are not
favorable. 13
Impact on Built and Natural Environments
Immediate Impact of Cyclones
The most serious immediate consequence of cyclones is the loss of human lives. It is estimated
that between 1960-1970, 17 major storms in various parts of the world killed about 350,000
people, most from drowning. The death rate is significantly higher where communications are
poor and warning systems and evacuation plans are inadequate. Furthermore, the number of
deaths will increase as population pressures force people to inhabit more vulnerable areas,
such as low-lying agricultural areas or overcrowded urban slums.
The most dramatic impact of cyclones is the damage they cause to houses and other physical
structures. In addition to damaging homes and buildings, cyclones destroy or damage critical
facilities, supply lines, crops, and/or food stocks. They disrupt economic activities and create
financial burdens. They may destroy or damage facilities that are critical not only for responding
to disasters, but also for maintaining a safe environment and public order. Among these are
communications installations; electrical generating and transmission facilities; water storage,
purification, and pumping facilities; sewage treatment facilities; hospitals; police stations; and
various other public and private buildings.
Cyclones disrupt agriculture and destroy crops. High winds destroy some standing crops,
especially grains, and damage orchards and forests. Flooding from intense rains damages
certain crops, especially tubers, and may cause excessive erosion. Storm surges scour and
erode topsoils, deposit salts on fields, and may increase salinity in subsurface water.
Furthermore, access to markets for buying and selling agricultural produce may be impeded by
damage to roads, bridges, railways, etc.