Download Unit 3.c. – Extreme weather events and their impact on people and

Unit 3.c. – Extreme weather events
and their impact on
people and property
-Hurricane formation & structure
-Case study of one hurricane to
illustrate:
- its effects on people & property
-protective measures used to reduce loss
of life and damage to property
Names: hurricanes (Atlantic Ocean)
typhoons (Pacific Ocean)
tropical cyclones (Indian Ocean)
• CHARACTERISTICS:
• Intense system of low pressure
– Very low troughs, 930mb or less
– About 50 per yr off W Africa of which 10% form a full hurricane
• Characterised by winds of extreme velocity & torrential
rainfall
• Develop over warm tropical seas (+26C) & where there
is depth to the ocean
- Constant supply of warm moist air evaporating is the fuel
- RH must be greater than 60%
- Need a large area of uniform temp., pressure & humidity
• Move generally from E to W
- In N hemisphere move to NW and then to NE
• Most form in autumn when sea temp. are highest & in
the trade wind belt
More characteristics:
• Located between 5-20 degrees N & S of the equator
- Hurricane free belt next to the equator because of a
very weak coriolis force (0-5 degrees)
- Rotation increases poleward giving the required ‘twist’
therefore most hurricanes form bet. 5-8 degrees N or
S
- form after ITCZ has moved to its most northerly extent
enabling air to converge at low levels
• Diameter of 200-500km
• Towering cumulonimbus clouds up to 12km
• Very quiet, calm eye of 30-50km where air is sinking
• 90% of deaths and injuries are caused by storm surge,
heavy rain and strong winds
Characteristics continued:
•
Average wind speeds 200km/hr (can reach
250km/hr)
•
3 classes of storms:
1. Tropical depression – thunderstorms with a
defined circulation, max. winds of 60km/hr
2. Tropical storm – winds up to 118km/hr
3. Hurricanes – anything above 119km/hr
Formation
Small scale instability
Warm, humid air rises
Rotation of the earth gives rise to a twist & the system
revolves
Large amounts of latent heat energy released through
condensation
Instability draws in more humid air, increases the size of
the system
System is self growing as long as there is a supply of
warm, moist air
• Characteristics of eye:
- Eye develops when
storm has reached
maturity
-Subsiding air 30-50km
in diameter
-Light winds, clear skies,
high temp.
-decending air increases
instability by warming &
exaggerates the storm’s
intensity
• Decline of storm:
-rapidly declines once the
source of heat is removed
i.e. when it moves over
colder water or a land
surface
increased friction &
cannot supply sufficient
moisture
-average lifespan of a
tropical cyclone is 7-14
days
Popular topics in exams:
• There is a general falling trend in deaths from
hurricanes e.g. the 5 highest figures were before
1939.
• Why?
• Better predictions i.e. use of aircraft
• Better evacuation / more forceful evacuation
• Better warning systems
• Better hospitals / medical care
• Better structure of buildings
• Better prepared for hurricanes, education on
precautions
Popular topics in exams:
• There is a general trend of increasing costs of
hurricane damage in million $ as time
progresses.
• Why?
• Rising population therefore more personal
belongings
• Marinas along the Gulf State house expensive
yachts etc.
• Expensive housing
• Improved infrastructure of airports, bridges,
flyovers etc would need repaired
Popular exam topics
• Why do LEDCs suffer more from the after
effects of hurricanes than MEDCs?
Past short questions
1. For a mature hurricane what is the:
-Max. cloud height
-Diameter
-Pressure
-Max. wind speed
(3) Jan 04
2. Explain why hurricanes form in tropical areas where there is a high
ocean temperature.
(3) Jan 04
3. Why do hurricanes not form between 5 N and 5 S of the equator?
(2) Jan 04
4. Describe and explain the relationship between the development of
hurricanes and a sea temperature of above 27C. (5) Jan 03
Past long questions (12 marks)
1.
With reference to your case study of a hurricane,
describe the protective measures used to reduce loss
of life and damage to property. Jan 2003
2.
With reference to your case study, describe the effects
of a hurricane on people and property. June 2004
3.
With reference to extreme weather events:
* describe and explain the formation of hurricanes; and
* describe the effects of one hurricane you have
studied on people and property. Jan 2005
Research task
Case study is Hurricane Katrina 2005
1. Make a list of causes
2. List the main warnings given
3. List the main precautions taken, including evacuation
4. What emergency aid was provided
5. How successful were the government warnings &
provision of aid?
6. List the effects of the hurricane on:
a) people
b) property