The main effects of tropical cyclones include heavy rain, strong wind, large
storm surges at landfall, and tornadoes. The destruction from a tropical cyclone
depends mainly on its intensity, its size, and its location. Tropical
cyclones act to remove forest canopy as well as change the landscape near
coastal areas, by moving and reshaping sand dunes and causing extensive erosion
along the coast. Even well inland, heavy rainfall can lead to mudslides and
landslides in mountainous areas. Their effects can be sensed over time by
studying the concentration of the Oxygen-18 isotope within caves within
the vicinity of cyclones' paths. After the cyclone has passed,
devastation often continues. Standing water can cause the spread of disease,
and transportation or communications infrastructure may have been destroyed,
hampering clean-up and rescue efforts. Nearly two million people have died
globally due to tropical cyclones. Despite their devastating effects,
tropical cyclones are also beneficial, by potentially bringing rain to dry
areas and moving heat from the tropics poleward. Out at sea, ships take
advantage of their known characteristics by navigating through their weaker,
western half. When a cyclone hits it causes PST
hazards. PST is an acronym standing for Primary, Secondary and Tertiary. A
primary hazard involves destructive winds, debris and storm surge. Secondary
hazard is flooding, fires and of course fresh water flooding. Finally Tertiary
hazards involves food prices that go majorly up and other long term hazards
like water poisoning. At sea
A mature tropical cyclone can release heat at a rate upwards of 6x1014 watts.
Tropical cyclones on the open sea cause large waves, heavy rain, and high winds,
disrupting international shipping and, at times, causing shipwrecks. Generally,
after its passage, a tropical cyclone stirs up ocean water, lowering sea
surface temperatures behind it. This cool wake can cause the region to be
less favorable for a subsequent tropical cyclone. On rare occasions, tropical
cyclones may actually do the opposite. 2005's Hurricane Dennis blew warm water
behind it, contributing to the unprecedented intensity of Hurricane
Emily, which followed it closely. Hurricanes help to maintain the global
heat balance by moving warm, moist tropical air to the mid-latitudes and
polar regions. Were it not for the movement of heat poleward, the tropical
regions would be unbearably hot. = North American colonization =
Shipwrecks are common with the passage of strong tropical cyclones. Such
shipwrecks can change the course of history, as well as influence art and
literature. A hurricane led to a victory of the Spanish over the French for
control of Fort Caroline, and ultimately the Atlantic coast of North America, in
1565. The Sea Venture was wrecked near Bermuda in 1609 which led to the
colonization of Bermuda and provided the inspiration for Shakespeare's The
Tempest. = Shipping =
Mariners have a way to safely navigate around tropical cyclones. They split
tropical cyclones in two, based on their direction of motion, and maneuver to
avoid the right segment of the cyclone in the Northern Hemisphere. Sailors term
the right side the dangerous semicircle since the heaviest rain and strongest
winds and seas were located in this half of the storm, as the cyclone's
translation speed and its rotational wind are additive. The other half of the
tropical cyclone is called the navigable semicircle since weather conditions are
lessened in this portion of the storm. The rules of thumb for ship travel when
a tropical cyclone is in their vicinity are to avoid them if at all possible and
do not cross their forecast path. Those traveling through the dangerous
semicircle are advised to keep to the true wind on the starboard bow and make
as much headway as possible. Ships moving through the navigable semicircle
are advised to keep the true wind on the starboard quarter while making as much
headway as possible. Upon landfall
The most significant effects of a tropical cyclone occur when they cross
coastlines, making landfall. = Strong winds =
Strong winds can damage or destroy vehicles, buildings, bridges, personal
property and other outside objects, turning loose debris into deadly flying
projectiles. In the United States, major hurricanes comprise just 21% of all land
falling tropical cyclones, but account for 83% of all damage. Tropical cyclones
often knock out power to tens or hundreds of thousands of people,
preventing vital communication and hampering rescue efforts. Tropical
cyclones often destroy key bridges, overpasses, and roads, complicating
efforts to transport food, clean water, and medicine to the areas that need it.
Furthermore, the damage caused by tropical cyclones to buildings and
dwellings can result in economic damage to a region, and to a diaspora of the
population of the region. = Storm surge =
The storm surge, or the increase in sea level due to the cyclone, is typically
the worst effect from landfalling tropical cyclones, historically
resulting in 90% of tropical cyclone deaths. The relatively quick surge in
sea level can move miles/kilometers inland, flooding homes and cutting off
escape routes. The storm surges and winds of hurricanes may be destructive
to human-made structures, but they also stir up the waters of coastal estuaries,
which are typically important fish breeding locales.
= Heavy rainfall = The thunderstorm activity in a tropical
cyclone produces intense rainfall, potentially resulting in flooding,
mudslides, and landslides. Inland areas are particularly vulnerable to
freshwater flooding, due to residents not preparing adequately. Heavy inland
rainfall eventually flows into coastal estuaries, damaging marine life in
coastal estuaries. The wet environment in the aftermath of a tropical cyclone,
combined with the destruction of sanitation facilities and a warm
tropical climate, can induce epidemics of disease which claim lives long after
the storm passes. Infections of cuts and bruises can be greatly amplified by
wading in sewage-polluted water. Large areas of standing water caused by
flooding also contribute to mosquito-borne illnesses. Furthermore,
crowded evacuees in shelters increase the risk of disease propagation.
Although cyclones take an enormous toll in lives and personal property, they may
be important factors in the precipitation regimes of places they
affect and bring much-needed precipitation to otherwise dry regions.
Hurricanes in the eastern north Pacific often supply moisture to the
Southwestern United States and parts of Mexico. Japan receives over half of its
rainfall from typhoons. Hurricane Camille averted drought conditions and
ended water deficits along much of its path, though it also killed 259 people
and caused $9.14 billion in damage. On the other hand, the occurrence of
tropical cyclones can cause tremendous variability in rainfall over the areas
they affect: indeed cyclones are the primary cause of the most extreme
rainfall variability in the world, observed in places such as Onslow and
Port Hedland in subtropical Australia where the annual rainfall can range from
practically nothing with no cyclones to over 1,000 millimetres if cyclones are
abundant. = Tornadoes =
The broad rotation of a land falling tropical cyclone often spawns tornadoes,
particularly in their right front quadrant. While these tornadoes are
normally not as strong as their non-tropical counterparts, heavy damage
or loss of life can still occur. Tornadoes can also be spawned as a
result of eyewall mesovortices, which persist until landfall.
Deaths During the last two centuries, tropical
cyclones have been responsible for the deaths of about 1.9 million people
worldwide. It is estimated that 10,000 people per year perish due to tropical
cyclones. The deadliest tropical cyclone was the 1970 Bhola cyclone, which had a
death toll of anywhere from 300,000 to 500,000 lives.
= United States = Before Hurricane Katrina, the average
death rate for tropical cyclones in the United States was decreasing. The main
cause of storm-related fatalities was shifting away from storm surge and
towards freshwater flooding. However, the median death rate per storm had
increased through 1979, with a lull during the 1980-1995 period. This was
due to greater numbers of people moving to the coastal margins and into harm's
way. Despite advances in warning strategies and reduction in track
forecast error, this increase in fatalities is expected to continue for
as long as people migrate towards the shore.
Reconstruction and repopulation While tropical cyclones may well
seriously damage settlement, total destruction encourages rebuilding. For
example, the destruction wrought by Hurricane Camille on the Gulf coast
spurred redevelopment, greatly increasing local property values.
Research indicates that the typical hurricane strike raises real house
prices for a number of years, with a maximum effect of between 3 percent to 4
percent three years after occurrence. However, disaster response officials
point out that redevelopment encourages more people to live in clearly dangerous
areas subject to future deadly storms. Hurricane Katrina is the most obvious
example, as it devastated the region that had been revitalized after
Hurricane Camille. Many former residents and businesses do relocate to inland
areas away from the threat of future hurricanes as well.
In isolated areas with small populations, tropical cyclones may cause
enough casualties to contribute to the founder's effect as survivors repopulate
their place. For example, around 1775, a typhoon hit Pingelap Atoll, and in
combination with a subsequent famine, reduced the island's population to a low
level. Several generations after the disaster, as many as 10% of Pingelapese
have a genetic form of color-blindness called achromatopsia. This is due to one
of the survivors of the depopulation brought on by the typhoon having a
mutated gene, which the population bottleneck caused to be at a
higher-than-usual level in succeeding generations.
Effects on natural resources = Geomorphology =
Tropical cyclones reshape the geology near the coast by eroding sand from the
beach as well as offshore, rearranging coral, and changing dune configuration
onshore. Their rain water gets absorbed into stalagmites within caves, creating
a record of past tropical cyclone impacts.
Coastal ridges Waves and storm surges accompanying
tropical cyclones erode undersea sands, erode shell deposits, break off corals
from near shore reefs in their paths, and carry all this detritus landwards in
a rolling wave of material that is deposited onshore, above highest
astronomical tide as a ridge of sand, shell and coral. For example, each
severe tropical cyclone crossing northeast Australia's tropical coastline
since the last significant change in sea levels has 'emplaced' such ridges within
the coastal landscape forming, in some places, series of ridges and a
geomorphological record of highest magnitude cyclones hitting the coast
over 3000 – 5000 years. Eyewitness accounts verify ridges of
this kind are formed by severe tropical cyclones and two clear examples cited
are the 18 kilometres long, 35 metres wide, 3.5 metres high coral shingle
ridge deposited on Funafuti Atoll by Tropical Cyclone Bebe in October 1971,
and the large coral shingle ridge deposited on Jaluit Atoll by Typhoon
Ophelia in January 1958. In tropical northeast Australia, an intense tropical
cyclone hit in March 1918, at which time there were eyewitness accounts of a 4.5
metres to 5.1 metres high ridge of pumice being deposited by that cyclone's
surge as it crossed the coast.). Limestone cave stalagmites
When tropical cyclones cross land, thin layers of calcium carbonate of unusually
'light' Oxygen isotope composition are deposited onto stalagmites in limestone
caves up to 300 kilometres from the cyclone's path.
As the cloud tops of tropical cyclones are high and cold, and their air is
humid - their rainwater is 'lighter'. In other words, the rainfall contains
significantly higher quantities of unevaporated Oxygen-18 than other
tropical rainfall. The isotopically lighter rainwater soaks into the ground,
percolates down into caves, and, within a couple of weeks, Oxygen-18 transfers
from the water into calcium carbonate, before being deposited in thin layers or
'rings' within stalagmites. A succession of such events created within
stalagmites maintain a record of cyclones tracking within a 300
kilometres radius of caves going back centuries, millennia, or even millions
of years. At Actun Tunichil Muknal cave in central
Belize, researchers drilling stalagmites with a computer- controlled dental drill
accurately identified and verified evidence of isotopically light rainfall
for 11 tropical cyclones occurring over a 23 year period.
At the Chillagoe limestone caves in northeast Australia inland from Cairns)
researchers identified and matched evidence of isotopically light rainfall
with 100 years of cyclone records, and from this have created a record of
tropical cyclones from 2004 back to 1200 A.D..
= Landscapes = Severe tropical cyclones defoliate
tropical forest canopy trees, remove vines and epiphytes from the trees,
break tree crown stems, and cause tree falls. The degree of damage they do
along their paths, at a landscape level), can be catastrophic yet variable
and patchy. Stripping trees and scattering forest debris also provides
fuel for wildfires, such as a blaze that lasted three months in 1989 and burned
460 square miles of forest that had been stripped by Hurricane Gilbert.
Wind velocity gradients or horizontal wind shear.
Degree of exposure; and Ecosystem species composition and forest
structure Assessments of cyclone damage done to
tropical rainforest landscapes in northeast Australia, have produced the
following typology for describing and 'mapping' the variable impacts they have
along their paths, as follows: Severe and extensive closest to the
centre of cyclone: impact appears to be multidirectional and is evidenced by
crowns of most trees having been broken, smashed or windthrown
Severe and localised closer to the cyclone centre than its edge: direction
of the destructive winds is clearly identifiable, and severe canopy
disruption is limited to the windward aspect of these forested areas
Moderate canopy disturbance closer to cyclone edge than its centre: most of
the tree stems are still standing, with only some treefalls, and most of the
damage is the defoliation of the canopy and branch breakage;
Slight canopy disturbance closest to cyclone edge: occasional stem fall or
branch breakage, with most of the damage consisting of loss of foliage on the
forest edges only, subsequently followed by leaf damage and heavy leaf litter
falls. See also
List of wettest tropical cyclones by country
References