OCR A2 GEOGRAPHY climatic hazard notes.

mainly from michael raw and official oct text books. our teacher was rubbish so i made my own notes. 

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  • Created on: 21-05-12 10:24
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Climatic hazards
Content: The study of the development of tropical storms and tornadoes to illustrate:
The atmospheric surface conditions that give rise to their development.
An understanding, with examples of how such systems develop;
Through examples, the hazards they present to particular areas and the impacts these hazards can
Hurricanes are compound hazards that include; heavy rainfall, strong winds, high waves and can cause other
hazards such as mudslides and flooding. They are intense hazards that affect large areas but are difficult to
predict accurately. The onset of any individual hurricane is rapid. They may travel slowly at first, but their
path is erratic. Hence it is not always possible to give more than 12 hours notice. This is not usually enough
time for proper evacuation and precautionary measures.
Conditions needed:
Sea temperatures must be over 27oC energetic evaporation from warm water carries latent heat
energy into the atmosphere. When condensation occurs, this energy is released, helping to generate
the very strong winds) and a deep layer of warm water down to 60-70m. This warm layer prevents cold
water rising to the surface and killing the system.
The low-pressure area has to be far enough away from the equator so that the Coriolis effect creates
rotation in the rising air mass ­ if it is too close to the equator there is insufficient rotation and a
hurricane will not develop. (Coriolis effect: deflecting force produced by the rotation of the earth,
deflecting objects to the right of their path in the northern hemisphere and left of their path in the
southern hemisphere.)
High humidity and therefore plenty of water vapour.
Hurricanes normally develop as intense low-pressure systems over tropical oceans. Winds spiral rapidly
around a calm central area known as the eye. Diameter of a hurricane may be up to 800km although
the very strong winds that cause most of the damage are found in the narrower belt up to 300km
Usually develop in the westward flowing air just north of the Equator (known as the easterly wave).
Initially start as small scale tropical disturbances or depressions, which are localised areas of low
pressure that cause warm air to rise.
Tropical disturbances cause thunderstorms that persist for at least 24 hours. These may develop into
tropical storms which have greater wind speeds of up to 117 km/h (73mph) however only about 10%
ever become hurricanes ­ storms with wind speeds of 118km/h (above 74mph).
Hurricanes are also characterised by high-intensity volumes of rainfall ­ up to 500mm in 24 hours
invariably causing flooding on land.
Once the rising air has become established (a convection cell), the system is self-perpetuating as long
as conditions remain favourable.
The rising air releases large quantities of heat during condensation. This reinforces the instability of the
rising air within the hurricane.
At the eye of the hurricane air descends from the top of the system, as it does it is warmed and
therefore able to hold more moisture ­ condensation is reduced and the eye remains cloudless.
Hurricane structure and effects
Hurricane winds can cause 15m waves in the open ocean, 6m on landfall.
In mature hurricanes pressure may fall to as low as 880-970 milibars, this strong contrast in pressure
between the eye and the outer part of the hurricane leads to strong gale force winds.

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Bordering the eye of most hurricanes is the eye wall: a ring of tall thunderstorms that produce heavy
rains and very strong winds. This is the most destructive part of the storm. Curved bands of clouds
surround the eye wall and trail away in a spiral fashion. These could bands produce heavy bursts of rain
and strong winds.
A mature hurricane is typically 200-500km in diameter, with clouds up to 12km in height.…read more

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Wind speeds can reach up 250 km/h-1 in the wall of the hurricane with gusts of up to 350 km/h-1
Destruction results from both direct impact and flying debris.
Primary cause of damage to trees and crops; entire forests can be flattened by hurricane force winds,
tall buildings are also vulnerable to collapse.
Sudden pressure changes may cause buildings to explode whilst suction can lift up roofs and entire
However most destruction, death and injury is due to flying debris.…read more

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Tornadoes are among the world's most violent, extreme weather conditions. They are a complex
phenomenon and are difficult to study. They are particularly common in parts of the USA and in the UK. The
UK holds the record for the greatest density of tornadoes per km2, although they tend to be small-scale.
Damage is related to the strength of the tornado and the materials that buildings are constructed of.
Management is very difficult.…read more

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Impacts of Tornadoes:
In an average year, about 1000 tornadoes are reported across the USA.
They cause around 80 deaths and over 1500 injuries.
Damage from tornadoes is mainly from three components: strong winds, strong rotational
movements and very low atmospheric pressure near the vortex.
Winds can reach 500km h-1, winds of this strength can pick up cars, and rip houses to shreds. Damage
paths can exceed 1.5km wide and 80km long.
Intense rainfall and damaging hailstorms.…read more

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Polar continental (Pc): air masses originate over central Canada and Siberia. The air is cold, dry and cloud
free giving extremely cold weather in the UK. In the summer months, heating at the base of the air
mass makes it less stable and cloudier.
Tropical Continental (Tc): air masses originate over hot deserts. They are hot, dry and unstable, and
deficient in moisture.
Tropical Maritime (Tm): air comes from the oceans of lower latitudes.…read more

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UK since 1703, bringing with it gusts of up to 167 km (104mph). The worst gusts were during the
night ­ had they been during the day the effects would have been much greater. The total cost of insurance
claims was over £860 million, but this figure could have been much higher.
Low Pressure ­ Depressions:
Depressions are areas of low pressure, up to 3000km in diameter, which develop on the polar front jet
stream.…read more

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Low wind chill can cause hypothermia or frostbite. Frostbite is a severe reaction to cold that can lead
to permanent tissue damage. Hypothermia is a condition in which the temperature of the body falls
below 35 oC, which can lead to a coma and death.
Blizzards are also associated with other hazards and dangers, such as power cuts when strong winds
and heavy snow bring down power cables. Liquids in pipes can freeze and fuel supplies may be cut off
because of disruptions to communications.…read more

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Drought is an extended period of dry weather leading to conditions of extreme dryness.
Absolute drought is a period of at least 15 consecutive days with less than 0.2mm of rainfall.
Hazards associated with droughts are; crop failures, heat stroke, forest fires, increased electricity
consumption due to air conditioning and smog.
Anticyclonic Blocking:
Blocking is a common synoptic situation in Western Europe. It occurs when a large, slow moving
anticyclone becomes established over the continent, disrupting the normal westerly circulation.…read more


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