Impacts of Tropical Cyclones Horace H P Burton

Impacts of Tropical Cyclones Horace H. P. Burton and Selvin De. C. Burton Caribbean Institute for Meteorology and Hydrology Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

Outline • Improved forecasting and warning system responsible for reductions in fatalities • Property losses are attributed to accelerated property development in coastal zones Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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. Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

Wind • Other factors * maximum wind speed in gusts * duration of high sustained wind speeds * variations in the direction of the wind * topography * debris Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

Rainfall • Several factors affect heavy rain from tropical cyclones * duration of rainfall (speed of motion) * energy/moisture supply * topography. Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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. Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

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 Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology

Economic Impact • Direct or indirect costs * damage * preparedness * warning service * relief * loss in business revenue. * losses to agriculture. Caribbean Disaster Mitigation Project Caribbean Institute for Meteorology and Hydrology