Meteorological Hazards

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Meteorological Hazards

• Large-scale storms

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Tropical Cyclones, Hurricanes and Typhoons
Intense cyclonic storms which originate over warm
tropical waters. The worst in terms of death and
destruction and most widespread naturally
occurring environmental hazard. Energy equivalent
10M tons of TNT- 41.5 million, billion Joules
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Katrina August 2005
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Katrina
Wikipedia link
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Associated hazards

• Storm Surge water is piled up along a coastline
  by strong winds and low pressure leading to
• drowning
• inundation
• erosion
• loss of fertility
• damage to buildings and transport networks

NOAA
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"The greatest potential for loss of life related
to a hurricane is from the storm
surge." - Brian Jarvinen, National Hurricane
Center
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• Strong winds
• destruction of property and crops
• spreading of fires
• http//www.nhc.noaa.gov/HAW2/english/high_winds.sh
  tml
• Rain
• loss of life, property damage and crop
  destruction through flooding
• contamination of water supplies
• landslides and mud flows
• http//www.nhc.noaa.gov/HAW2/english/inland_flood.
  shtml

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• Earthquakes
• large pressure changes over a matter of
  hours ( 2-3 million tonnes km-2), tidal waves or
  surges (10-12m) can increase pressure on the
  surface by 7 million tonnes km-2 (eg Tokyo quake
  of 1923)

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Classification

• disturbance - rotary circulation apparent at high
  levels - no strong winds - isobars discontinuous
• depression - rotary circulation extends to the
  surface -maximum sustained winds of 38 mph or
  less - at least one closed isobar.
• storm - an organized system of strong
  thunderstorms - maximum sustained winds of 39-73
  mph (63kmh-1- 119kmh-1 )
• hurricane - An intense tropical weather system of
  strong thunderstorms sustained wind speeds exceed
  119kmh-1

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Formation of Hurricanes

• Warm oceans (26-270C)
• Convergence of air
• Inner subsidence of air

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Warm oceans (26-270C)
Temps reach 260C Dec-May in South, June-Oct in
North. Easterly trades blow warm surface waters
to Westerly side of oceans
Cyclonic depressions form when water temp reaches
240C - eye structure requires 26-270C
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Average number of tropical cyclones per year
(1952-71)
Bryant (1991) p20
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Intertropical convergence zone
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Inter-tropical convergence zone
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Highs and Lows
Convergence of air caused by easterly wave
development in the trade winds
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Latent Heat
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Energy Source latent heat
334kJ kg-1
2260kJ kg-1
420kJ kg-1
1cal4.186J
334kJ kg-1
420kJ kg-1
2260kJ kg-1
334kJ kg-1
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Depression - Storm - Hurricane
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• Convergence causes convective instability
• Enhanced by release of latent heat of
  condensation
• Core heating maintains temps 200C above
  surroundings
• Intense convection causes more air to be sucked
  in from larger area
• Air rotates as a result of coriolis effect
  producing wind vortex

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Inner subsidence of air
If convective zone increases to around 10-100km
then subsidence of air takes place at the centre
as well as at the sides. Inner subsidence
abruptly terminates forming a wall, intensifying
upward spiralling convection against it.
Subsidence causes stability in the eye -
cloud evaporates and calm winds result. Eye will
not be stable if upper horizontal wind speeds
exceed those on the ground by 10ms-1 instead
vertical structure gets displaced downwind.
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Storm Surges
main cause of death in Bangladesh in 1970 and
1985 cyclones, and also of destruction in 1953
North Sea Storm
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Galveston 1900
                       Detected over the tropical
Atlantic on August 27. Reached Cuba as a tropical
storm on September 3, reached the Texas coast
south of Galveston late on September 8 as a
Category 4 hurricane. This hurricane was the
deadliest weather disaster in United States
history. Storm tides of 8 to 15 ft inundated the
whole of Galveston Island, as well as other
portions of the nearby Texas coast. These tides
were largely responsible for the 8,000 deaths
(estimates range from 6,000 to 12,000) attributed
to the storm. The damage to property was
estimated at 30 million.
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Andrew 1992
Started modestly as a tropical wave that emerged
from the west coast of Africa on August 14. The
wave spawned a tropical depression on August 16,
which became Tropical Storm Andrew the next day.
Andrew reaching hurricane strength on the 22nd
and Category 4 status on the 23rd. After briefly
weakening over the Bahamas, Andrew regained
Category 4 status as it blasted its way across
south Florida on August 24. 142 mph sustained
winds with gusts to 169 mph (measured 144 ft
above the ground), Center had a peak gust of 164
mph (measured 130 ft above the ground), while a
177 mph gust was measured at a private home.
Andrew produced a 17 ft storm surge near the
landfall point in Florida, while storm tides of
at least 8 ft inundated portions of the Louisiana
coast. Andrew also produced a killer tornado in
southeastern Louisiana. Andrew is responsible for
23 deaths in the United States and three more in
the Bahamas. The hurricane caused 26.5 billion
in damage in the United States, of which 1
billion occurred in Louisiana and the rest in
south Florida. The vast majority of the damage in
Florida was due to the winds. Damage in the
Bahamas was estimated at 250 million.
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http//rsd.gsfc.nasa.gov/rsd/images/andrewSequence
_lg.jpg
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http//www.nhc.noaa.gov/HAW2/english/history/1900_
MEOW.gif
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Extra-tropical cyclones

• low pressure cells that develop along the polar
  front - also develop over warm waters off the
  East coast of Australia, Japan and USA.

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East-coast cyclones

• easterly moving pressure systems passing over
  mountains meets warm poleward-flowing current.
• East coast of Japan - Japanese Alps and Kuroshio
  current
• USA - Appalachians and Gulf Stream
• Australia - Great Dividing Range and East
  Australian current
• Not associated with any frontal structure -
  develop in upper atmosphere - can develop the
  structure of a tropical cyclone.

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World cyclone disasters

• Bangladesh - then East Pakistan (1970). - more
  people killed by storm surge rather than strong
  winds (repeated in 1985) - led to formation of
  Bangladesh - but never recovered and became
  poorest nation in the world.
• Most people are killed during cyclones by floods
  - typically 100mm rain dumped per day within
  200km of eye, 30-40mm over area 200-400km from
  eye.
• Between 1851 and 1866 40-50 million people died
  along the Yangste river because of tropical
  cyclone induced rain.

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Japan 1281

• Kublai Khan invaded Japan - set to break through
  Samurai defences until Typhoon swept through
  battlefield destroying 1000 invading ships and
  trapping 100,000 attacking soldiers who were
  drowned or killed by Japanese. Kamikaze - Divine
  Wind.

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• Depends on the economic development of a country
  and its transport and communication
  infrastructure.
• Design and construction of buildings is a crucial
  factor
• Destruction of crops and contamination of water
  supplies can lead to consequential deaths due to
  starvation.
• International commodity markets - Hurricane
  Flora - Cuba 1963 caused sugar prices to rise.

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Australia - North coast

• Generally accepted that cyclones will occur.
• Evacuation takes place near shore on good travel
  networks
• Strict building codes - policed and adhered to
  Network of tracking stations - reported over TV
  and radio
• Population trained and prepared
• Disaster coordinating centre exists  - the
  director can have overriding powers - but the
  measures taken (evacuation, re-location,
  rebuilding) can have long term damaging effects
  on families and communities.

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Bangladesh

• Bay of Bengal has history of destructive storm
  surges - hundreds of thousands have been killed
  in many major storms
• Dutch engineers, financed by the World Bank built
  embankments and dams at the mouth of the Ganges -
  but they were not designed to withstand storm
  surge. Settlement by illiterate farmers was
  allowed to relieve congestion elsewhere.
• November 1970 cyclone detected by satellite three
  days in advance but warning was only given by the
  Pakistan Meteorology Bureau the evening that the
  cyclone struck (to the single radio station after
  it had closed!)

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Bangladesh

• Much of reclaimed land had inadequate transport
  links to safe land -evacuation impossible.
• Recent immigrants had no knowledge of storm surge
  and were ill prepared.
• In middle of the night storm surge 15m high
  struck - killed 500 000 people, 1m head of
  livestock, inundated 400 000 hectares of rice
  paddy. Over 50m people were affected.
• Pressure for land so great that area was
  repopulated and devastation was repeated in 1985.

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Polar-front  lows (40o N and S of equator)

• low pressure cells develop along the polar front
  with diameters 2000km.
• travel easterly
• location depends on the "Rosby waves" in polar
  front

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Examples

• Eastern seaboard of USA
• North sea region
• Middle ages saw cataclysmic storms - huge social
  impact - dramatic effect on coastline of Northern
  Europe
• All Saints Day Flood 1-6 November 1570 400,000
  people killed in Western Europe
• Erosion of Heligoland - 60km - 25km between 800
  and 1300AD - Gulf of the Zeider Zee formed by
  Lucia storm of 14 Dec 1287

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Figure 2-7 The economic losses from catastrophic
weather events have risen globally 10-fold
(inflation-adjusted) from the 1950s to the 1990s,
much faster than can be accounted for with simple
inflation. The insured portion of these losses
rose from a negligible level to about 23 in the
1990s. The total losses from small,
non-catastrophic weather-related events (not
included here) are similar. Part of this observed
upward trend in weather-related disaster losses
over the past 50 years is linked to
socio-economic factors (e.g., population growth,
increased wealth, urbanization in vulnerable
areas), and part is linked to regional climatic
factors (e.g., changes in precipitation, flooding
events).