Causes, Impacts & Associated Secondary Hazards

8/8/2019 Causes, Impacts & Associated Secondary Hazards

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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

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Causes, Impacts & Associated Secondary Hazards