Impacts of Tropical Cyclones

1
Impacts ofTropical Cyclones
Horace H. P. Burton and Selvin DeC.
Burton Caribbean Institute for Meteorology and
Hydrology
2
Outline

• Impacts of tropical cyclones detrimental on
  developing countries
• Examples in the Caribbean - Gilbert in 1988
  Hugo in 1989 Luis in 1995 Georges in 1998
• Loss of lives has significantly decreased over
  recent years but loss of property has increased
  substantially

3
Outline

• Improved forecasting and warning system
  responsible for reductions in fatalities
• Property losses are attributed to accelerated
  property development in coastal zones

4
Wind

• Perhaps the best understood of all damage agents
• Fortunate as the winds largely determine,
  directly or indirectly, the other agents
• Low-level winds typically stronger on the right
  side of the cyclone in the Northern Hemisphere
• Highly variable both in time and space.

5
Wind

• Area of destruction varies from about 25 km in
  small systems to 500 km or more in large systems
• Damage a function of more than maximum wind

6
Wind

• Other factors
• maximum wind speed in gusts
• duration of high sustained wind speeds
• variations in the direction of the wind
• topography
• debris

7
Rainfall

• Rainfall associated with tropical cyclones is
  both beneficial and harmful
• Example - Mitch 1998
• over 9000 deaths from rain-induced flooding in
  portions of Central America
• in Honduras 900 mm of rain reported in 6 days
• highest daily rainfall of 466 mm on October 31

8
Rainfall

• Several factors affect heavy rain from tropical
  cyclones
• duration of rainfall (speed of motion)
• energy/moisture supply
• topography.

9
Rainfall

• Floods from tropical cyclones are dependent upon
• size and speed of the system
• physical characteristics of the drainage basin
  such as the soil type, the degree of saturation
  of the ground, and the vegetation which control
  runoff
• rate and total amount of precipitation.

10
Storm Surge

• Storm surge - an abnormal rise of water due to a
  tropical cyclone
• Surge is a response to meteorological and other
  driving forces
• Most important factor is the maximum wind speed
• Surges may vary from as little as 1 m or less to
  5 m or more

11
Storm Surge

• Potentially disastrous surges occur along coasts
  with low-lying terrain that allows inland
  inundation, or across inland water bodies such as
  bays, estuaries, lakes, and rivers leading to
  severe flooding
• Typical surge affects about 160 km of coastline
  for a period of several hours and may penetrate
  as much as 15 to 30 km inland

12
Wind Waves

• Wind blowing across a stretch of open water
  creates waves
• Wave heights depend on a number of factors
• length of time the wind has been blowing
• distance over which the wind has blown
• state of sea at time wind started to blow
• Average Atlantic hurricane waves are about 10 m

13
Surge and Wave Impacts

• Impacts of storm surge are coastal flooding,
  beach erosion, and the removal of beach materials
• Waves reshape coastal areas, wear away rocky
  shorelines, move sand - eroding or building beach
  areas - and damage structures in their paths
• Pounding nature of waves which accompany storm
  surge is responsible for most of damage to the
  structures

14
Surge and Wave Impacts

• Effect of a wave on a stretch of coastline is
  determined not only by strength of wave itself,
  but also by slope of bottom offshore, presence of
  coral reefs or other breakwaters, shape of the
  coastline
• Factors above can dissipate wave energy before it
  reaches the shore or concentrate it,
  significantly increasing local wave effects

15
Surge and Wave Impacts

• When combined with increased water levels from
  storm related surges, waves produced during a
  hurricane can reach areas typically shielded from
  the direct effects of waves, destroying buildings
  and dramatically altering the existing shoreline

16
Tornadoes

• Frequently spawned by hurricanes on crossing
  coastlines and islands, but have not been
  reported over the Caribbean
• Patterns of damage suggest that tornadoes may
  actually occur more often than reported
• More likely to occur in eyewall or rainbands
• Force of wind and sudden reduction in pressure
  major destructive impacts

17
Economic Impact

• Direct or indirect costs
• damage
• preparedness
• warning service
• relief
• loss in business revenue.
• losses to agriculture.