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CAUSES, IMPACTS &ASSOCIATED SECONDARYHAZARDS OF CYCLONES
Presented By:Sajid Mahmood Farooqi
Research Student University of Karachi
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SEQUENCE
Brain Storming (Your View) Introduction
Objective
Definitions
Causes
Impacts
Associated Secondary Hazards
Situation in Pakistan
Question Answer
Discussion & Suggestions
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YOUR VIEW
Q. What are the four conditions required for the
formulation of a cyclonic storm?
Q.Aside from strong winds, what other hazardsare associated with cyclonic storms?
Q.From your own experience, what has been
the greatest loss to communities caused by
tropical cyclones?
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INTRODUCTION
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OBJECTIVE
To get some back ground knowledge of thehazard we are gathered here for and to gain some
working knowledge that:
What a cyclone is?
How is it formed?
What are its Impacts?
What secondary hazards are associated with a
cyclone?
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DEFINITIONSA tropical cyclone is the generic term for a non-frontal
synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e.
thunderstorm activity) and definite cyclonic surface wind
circulation
Tropical Depressions: Max. sustained surface winds ofless than 17 m/s (34 kt, 39 mph).
Tropical Storm winds of at least 17 m/s (34 kt, 39 mph)
assigned a name.
If winds reach 33 m/s (64 kt, 74 mph)), then they are
called:
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IMPORTANT TROPICAL
CYCLONE BASINS
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DEFINITIONS CONTD.
a. Cyclones circulate counterclockwise in the Northern
Hemisphere and clockwise in the SouthernHemisphere.
Image Courtesy: NOAA, Cyclonic Storm on Thatta & Badin Districts on 20/05/1999.
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DEFINITIONS CONTD.
U.S. Name U.S.Saffir-
SimpsonCategory
Scale
NWPacific
Arabian Sea/Bay of Bengal
AustralianName
Australian
Category
TropicalDepression
-- TropicalDepression
Depressionor Severe
Depression
Tropical Low ---
Tropical Storm -- TropicalStorm
Cyclonic Storm TropicalCyclone
1
Tropical Storm -- SevereTropicalStorm
Severe CyclonicStorm
TropicalCyclone
2
Hurricane 1 Typhoon Very SevereCyclonic Storm
Severe TropicalCyclone
3
Hurricane 2 - 3 Typhoon Very SevereCyclonic Storm
Severe TropicalCyclone
4
Major 4 - 5 Super Super Cyclonic Severe Tropical 5Source: Commonwealth of Australia, Bureau of Meteorology.
b. Intensity of a tropical cyclone is determined according to
Saffir-Simpson Scale.
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Formation and initial development stage
Four atmospheric and oceanic conditions are necessary
for development of a cyclonic storm:1. A warm sea temperature in excess of 26 C, to a depth
of 60 m.
2. High relative humidity (degree to which the air is
saturated by water vapor) of the atmosphere to a heightof about 7000 m.
3. Atmospheric instability (an above average decrease of
temperature with altitude)
4. A location of at least 4-5 latitude degrees from the
Equator allows the influence of the forces due to the
earths rotation (Coriolis force) to take effect in inducing
cyclonic wind circulations around low pressure centers.
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tructur e
of
aTro
pical
Cy
clone
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IMPACTSTropical cyclones are characterized by their destructive winds, storm surges
and exceptional level of rainfall which may cause flooding.
Destructive winds:
The strong winds generated by a tropical cyclone circulate counter-
clockwise in the Northern Hemisphere, while spiraling inwards and
increasing toward the cyclone center. Wind speeds progressively increase
toward the core. 150 to 300 km from the center of a typical mature cyclone, winds of 63-
88 kph
100-150 km from the center, storm force winds of 89-117 kph
50 to 100 km from the center; winds in excess of hurricane force, 117
kph or greater
20 to 50 km from the center, on the edge of the inner core contains winds
250 kph or higher.
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A scale classifying the intensity of the storms, the Beaufort scale, estimates the wind velocity
by observations of the effects of winds on the ocean surface and familiar objects. Both the
United States (Saffir-Simpson Potential Hurricane Damage Scale) and Australia (Cyclone
Severity Categories) use country-specific scales which estimate potential property damage in
five categories.
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Storm Surges The storm surge, defined as the rise in sea level
above the normally predicted astronomical tide, is frequently a
key or overriding factor in a tropical storm disaster. The friction of strong on-shore winds on the sea surface.
Suction effect of reduced atmospheric pressure.
Pile up the sea water along a coastline near a cyclones
landfall. In cyclones of moderate intensity the surge effect is limited to
several meters.
In the case of exceptionally intense cyclones, storm surges of
up to eight meters can result.
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The major factors include:
a) A fall in the atmospheric pressure over the sea surface.
b) The effect of the wind.
c) The influence of the sea bed.
d) A funneling effect.
e) The angle and speed at which the storm approaches thecoast.
f) The tides.
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STORM SURGE
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Exceptional rainfall occurrences:
The worlds highest rainfall totals over one or twodays have occurred during tropical cyclones. Thehighest 12 and 24 hour totals, 114 cm and 182 cmhave both occurred during cyclones at La Reunion
Island in the SW Indian ocean. The very high specifichumidity condenses into exceptionally largeraindrops and giant cumulus clouds, resulting in high
precipitation rates. When a cyclone makes landfall,
the rain rapidly saturates even dry catchment areasand rapid runoff may explosively flood the usualwater courses and create new ones.
Associated Secondary Hazards
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Physical damage
Structures will be damaged or destroyed by wind
force, through collapse from pressure differentials, by
flooding, storm surge and landslides. Standing crops
may be lost to floods, storm surges, and sea water
salinity. Salt from storm surges may also be depositedon agricultural lands and increase ground water
salinity. Fruit, nut or lumber trees may be damaged or
destroyed by winds, flood or storm surges. Plantation
type crops such as banana and coconut are extremelyvulnerable.
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Erosion could occur from flooding and storm surges.Additional items subject to severe damage include
overhead power lines, bridges, culverts and drainage
systems. jetties and retaining walls, embankments and
coastal dikes, general lack of weatherproofing ofbuildings, huge losses to building work in progress,
scaffolding, marinas, and roofs of most structures.
Falling trees, wind-driven rain and flying debris cause
considerable damage.
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Casualties and public health
There are relatively few fatalities but there may be
numerous casualties requiring hospital treatment due
to the high winds associated with cyclonic storms.
Storm surges may cause many deaths but usually fewinjuries among the survivors. Due to flooding and
possible contamination of water supplies, malaria and
other viruses may be prevalent several weeks after the
flooding.
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Water supplies
Open wells and other ground water supplies may be
temporarily contaminated by flood waters and storm
surges. They be contaminated by pathogenic (diseaseproducing) organisms if bodies of people or animals are
lying in the sources or sewage is swept in. Normal water
sources may be unavailable for several days.
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Crops and food suppliesThe combination of high winds and heavy rains, even without
flooding, can ruin standing crops and tree plantations. Food
stocks may be lost or contaminated if the stores/structures in
which they were held have been destroyed or inundated. It is
possible that food shortages will occur until the next harvest. It is
also possible that tree and food crops may be blown down or
damaged and must be harvested prematurely.
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Communications and logistics
Communications may be severely disrupted astelephone lines, radio antennas and satellite disks are
brought down, usually by wind. Roads and railroadlines may be blocked by fallen trees or debris andaircraft movements will be curtailed for at least 12 to24 hours after the storm. Modes of transportation suchas trucks, carts and small boats may be damaged bywind or flooding. The cumulative effect of all damage
will be to impede information gathering and transportnetworks.
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CONDITIONS IN PAKISTAN
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Due to rarity of the phenomena this hazard has got
little attention which is also after the hazard strikes.Only three tropical cyclones of different intensitieshad made land fall on Pakistan Coasts.
Changing global climatic patterns are showing achange in the trends of occurrences of weather
related hazards. Pakistan coast being in the sub tropical location and
in close vicinity to warm waters might be hit bytropical cyclones in the future.
There is an ever increasing need to be prepared inadvance to cope with any such disastrous event inthe future.
CONDITIONS IN PAKISTAN
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QUESTIONS ?
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DISCUSSION &SUGGESTIONS