Strong winds (typhoons, hurricanes, cyclones, tropical storms and tornados)
Mechanism of destruction
Pressure and suction from wind pressure, buffeting for hours at
a time. Strong wind loads imposed on a structure may cause it to collapse,
particularly after many cycles of load reversals. More common damage is building
and non-structural elements (roof sheets, cladding, chimneys) blown loose.
Wind-borne debris causes damage and injury. High winds cause stormy seas that
can sink ships and pound shorelines. Many storms bring heavy rains. Extreme low
air pressure at the center of a tornado is very destructive and houses may
explode on contact.
Parameters of severity
Velocity of wind. Wind scales (e.g. Beaufort) gale severity
scale. Local hurricane/typhoon scales.
Winds generated by pressure differences in weather systems.
Strongest winds generated in tropics around severe low pressure systems several
hundreds of kilometers diameter (cyclones) known as typhoons in the Pacific and
as hurricanes in Americas and elsewhere. Extreme low pressure pockets of much
narrower diameter generate rapidly twisting winds in tornados.
Hazard assessment and mapping techniques
Meteorological records of wind speeds and direction at weather
stations gives probability of high winds in any region. Local factors of
topography, vegetation and urbanization may affect microclimate. Past records of
cyclone and tornado paths give common patterns of occurrence for damaging wind
Potential for reducing hazard
None. Cloud seeding may dissipate rain content.
Onset and warning
Tornados may strike suddenly but most strong winds build up
strength over a number of hours. Low pressure systems and tropical storm
development can be detected hours or days before damaging winds affect
populations. Satellite tracking can help follow movement of tropical storms and
project likely path. The movements of weather systems are however, complex and
still difficult to predict with accuracy.
Elements most at risk
Lightweight structures and timber housing. Informal housing
sectors and shanty settlements. Roofs and cladding. Loose or poorly attached
building elements, sheets and boards. Trees, fences, signs etc. Telegraph poles,
pylons and high-level cables. Fishing boats or other maritime industries.
Main mitigation strategies
Engineering of structures to withstand wind forces. Wind load
requirements in building codes. Wind safety requirements for non-structural
elements. Good construction practices. Micro-climatic siting of key facilities,
e.g. in lee of hillsides. Planting of windbreaks, planning of forestry areas
upwind of towns. Provision of wind-safety buildings (e.g. strong village halls)
for community shelter in vulnerable settlements.
Construction of wind-resistant or easily rebuilt houses.
Securing fixing of elements that could blow away and cause damage or injury
elsewhere, e.g. metal sheeting, fences, signs. Preparedness for storm action.
Taking shelter in strong, wind-resistant buildings. Protection measures for
boats, building contents or other possessions at