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Extreme Weather Hazards
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Learning objectives
What is an extreme weather hazard?
What are the causes and effects of massive
hurricanes, such as Hurricane Katrina?
What are the causes and effects of tornados?
What are the causes, effects and dangers of
other weather hazards?
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What is an extreme weather hazard?
A weather hazard is any naturally occurring weather condition
that has the potential to cause either harm or damage.
We need to understand
weather hazards so
that we can minimize
the risk to human life.
Weather hazards can have short-term and long-term effects.
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Short-term effects of extreme weather hazards
Short-term effects might include superficial
damage to land and buildings or a temporary
population migration from an area. Food
sources, power lines and supply
routes may also be temporarily
damaged by any number of weather hazards.
Short-term effects will only last a few days
or weeks. They will not cause any lasting
changes to the ecosystem, the population or
the ecology of the land.
Not being able to go to school due to too much
ice or snow on the roads would be a short-term
effect of a weather hazard.
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Long-term effects of extreme weather hazards
Long-term effects can include large-scale destruction of
property, or a complete alteration of the physical landscape.
Some weather hazards may permanently alter the ecosystem
through habitat destruction, which can have knock on effects
for many species.
This picture shows the
Chandeleur islands in the
USA, which have had
their geography,
permanently altered by
Hurricane Katrina. This
is a long-term effect of a
weather hazard.
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Short-term and long-term effects
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Learning objectives
What is a weather hazard?
What are the causes and effects of massive
hurricanes, such as Hurricane Katrina?
What are the causes and effects of tornados?
What are the causes, effects and dangers of
other weather hazards?
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How do hurricanes form?
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Hurricane Katrina
Hurricane Katrina was the most powerful hurricane to
hit the United States in known history.
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Hurricane Katrina
Hurricane Katrina hit New
Orleans on the morning of the
29th August 2005 bringing with it
terrible destruction.
Winds of over 250 kilometres
per hour were recorded as
Katrina hit the coast,
causing a storm surge
8.5 metres high.
New Orleans
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Effects of Hurricane Katrina
At first New
Orleans
seemed to have
weathered the
worst of the
hurricane,
but later
storm surges
breached
the city’s
protective levees.
The levees are walls and embankments built alongside
the rivers to keep New Orleans safe from flooding.
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Effects of Hurricane Katrina
80% of the city was flooded
and over a million homes
were left without electricity.
Over 1,800 deaths were
caused by the storm, around
700 of them in New Orleans.
In some areas the flood level
rose to over six metres. Those
that had decided to stay in their
homes had to either find high
ground and await rescue or
risk swimming and wading
through polluted floodwater.
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Effects of Hurricane Katrina
The storm forced over a million
people to leave their homes. It
also damaged oil refineries, spilling
24 million litres of crude oil. In total,
Hurricane Katrina caused over $81
billion worth of damage, making it
the costliest Atlantic hurricane ever.
Much of the damage is still being
felt. In June 2006, the population
of New Orleans was only about
half what it had been before the
hurricane and repairs on the levee
system were still unfinished.
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Dealing with Hurricane Katrina
For the mayor of New Orleans, Ray Nagin, Hurricane
Katrina was the greatest challenge he had ever faced.
Imagine yourself in his position–
you need to prepare the city as
best you can, monitor the
defences and communicate
effectively with state and
national organizations and
coordinate a relief effort during
a time of great crisis.
Which part of this job would you find the most stressful?
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Decide the alert level
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Hurricane Katrina news report
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Learning objectives
What is a weather hazard?
What are the causes and effects of massive
hurricanes, such as Hurricane Katrina?
What are the causes and effects of tornados?
What are the causes, effects and dangers of
other weather hazards?
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Tornados
Tornados are one of nature’s most powerful forces.
Although hurricanes may be larger in size, the winds
inside a tornado are far more concentrated. This gives
them the power to cause extreme devastation wherever
they hit. Powerful tornados have produced wind speeds of
over 500 kmph, (about double those of Hurricane Katrina).
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Tornado formation
Tornados form where there is warm
air rising upwards from the ground.
If this rising, warm air then collides
with the descending cool air of an
oncoming thunderstorm, it can
produce a spinning vortex
(similar to the vortex you see when
you take the plug out of the bath).
If this spinning vortex, known as a
funnel cloud, has enough energy,
it grows larger until it eventually
hits the ground, forming a tornado.
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Where do tornados occur?
Tornados occur all over the world but a large percentage of
them form in an area of the USA known as Tornado Alley.
Tornados per year
<1
1–5
6–10
11–15
Tornado Alley
>15
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Tornado Alley
Tornado Alley in the USA is
particularly prone to tornados as
it is where cool, dry air moving
southwards from Canada, collides
with warm, humid tropical air moving
northwards from the Gulf of Mexico.
When the cold front and the warm
front meet, the combination of
warm rising air and cold falling air is
exactly right for tornado formation.
The tornado season in the USA
generally lasts from March
until August.
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Tornado Preparation
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•
•
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Listen to the weather (information from satellites)
Know what the warning sound is (siren)
Pick a safe lower room with few/no windows
Practice drills to make sure you know the way out
Make your safe room even safer by reinforcing it
Check trees and safety equipment
Tie up trash cans
Watch for danger signs
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Classifying tornados
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Learning objectives
What is a weather hazard?
What are the causes and effects of massive
hurricanes, such as Hurricane Katrina?
What are the causes and effects of tornados?
What are the causes, effects and
dangers from other weather hazards?
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Heatwaves
A heatwave is when a region experiences a prolonged period
of unusually hot weather. A heatwave in Britain may only reach
temperatures considered normal for other areas of the world,
but it will still be classed as a heatwave because it exceeds
that region’s normal temperatures.
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European heatwaves
In August 2003, Europe
suffered one of the most
extreme heatwaves
of recent time.
Temperatures in
France soared to up to
40°C. Over 50,00 people
died from the effects
of the heat, nearly 15,000
of them in France.
There were also
shortfalls in crop
production due to drought.
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Forest fires
Extreme heat can also bring with it the danger of fire.
Forest fire has been recognized as a natural part of the
ecosystem, with many plants and trees requiring fire for
germination of their seeds. The eucalyptus tree
even has flammable oil in its leaves to encourage
fire. Fire gives this tree an advantage over its
competitors as it is faster at re-growing.
However, forest fires
not only harm humans and
animals, they can also burn
away much of the vegetation
that prevents erosion. This can
sometimes result in landslides.
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Why do forest fires start?
Forest fires start when there is little rain and a lot of heat.
This dries out the soil, which causes the plants to release
ethylene, a flammable gas.
The combination of this and a
lot of dry fuel on the forest
floor, makes the environment
highly flammable.
Some fires can start through
spontaneous combustion - materials
like hay and tree resin will catch fire
if sufficiently heated. However,
lightening and human carelessness
cause most forest fires.
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Humans and forest fires
Human activity and carelessness cause the greatest number
of forest fires, however fires caused by lightning tend to burn
far larger areas, as often these occur in remote places and it
may be some time before fire-fighters are aware of them.
As human development
encroaches further into areas
of wild vegetation, the risk to
human life becomes far greater.
In recent years, cities like
Sydney, Australia and populated
areas in southern California have
all suffered great damage due to
large forest fires.
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Drought
Perhaps the most potentially dangerous
weather hazard to human life, is
long-term drought. Like heatwaves,
there may be relative differences in
drought conditions from region to region,
but all droughts result from lack of
available water. Without water, crops fail
and animals die, so droughts are often
followed by famines.
Disease is also prevalent during
droughts due to a lack of sanitation
and the pollution of water sources.
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Human activities and drought
Droughts are not just the result of weather
conditions. Human actions can also cause droughts.
Constructing dams may
severely affect the course
of a river, causing it to dry
up further downstream.
Deforestation (the removal
of forests) can dramatically
alter the soil’s ability to hold
water, drying out the ground
and triggering desertification.
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Match the definitions
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Lightning effects
It is thought that lightning strikes
occur 100 times every second. Most
of these strikes only happen within
storm clouds and never reach
Earth, but those that do can be very
dangerous.
One estimate suggests that over
2,000 people die each year from
lightning, but with many strikes
unreported or occurring in remote
areas, it is hard to gauge the real
number.
Central Africa has the highest rate
of lightning strikes per year.
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Why does lightning occur
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• Clouds need to form first over warm water or land.
• Clouds have to get very tall (cumulo - nimbus)
• Ice particles form at the top of the cloud and swirl around
touching against each other
• Water drops do the same at the bottom of the cloud
• When they rub against each other it makes static
electricity
• Like in a battery the negative charge is on one end of the
cloud and the positive on the other.
• When the charge in the cloud becomes to great it
discharges to the ground (the ground might produce a
spike first).
• The charge goes through the ions in the air and thunder
is the sound of air exploding
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Lightning facts
A lightening bolt contains
on average over 300 million
volts and can raise the air
temperature around it to
27,700°C, (about 5 times
that of the surface
temperature of the sun).
Lightning also moves
more than 15,000 times
faster than a bullet with the
average length of a lightning
streak being around six miles long.
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How does hail form?
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Hailstorm effects
Hailstorms can devastate crops and cause extensive
damage. On rare occasions, hailstones have grown
so large that their impacts have had fatal consequences.
The heaviest
hailstone ever
recorded had
a mass of over
one kilogram
and fell during
a storm in
India that
killed 92 people.
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Flooding
Flooding is the most frequently
occurring disaster in the world
today. Heavy rain concentrated in
a local area can cause water
levels to rise sharply which may
result in a flash flood. Flash
floods arise quickly with little
advance warning, like the flood
at Boscastle, England in 2004.
Flooding occurs when rivers cannot contain their waters and
overflow. Flooding can also occur when storms at sea drive
large amounts of water onto the coast which can surge past
flood defences.
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Flood defences
To combat the dangers of
flooding, humans have built
a variety of flood defences.
Dykes and levees act as
flood barriers along major
rivers. Dams make it possible
to control the amount of
water flowing through a river.
Sea walls and costal defences can help protect shorelines
from sea-flooding. The Thames barrier is a floating barrier
which can close to protect London from sudden tidal surges.
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Flood plains and wetlands
Although flood defences can
minimize the danger from
flooding to certain areas,
flooding is an natural event that
can never be fully controlled. In
many parts of the world,
flooding brings great benefits
as it spreads mineral-rich
silt and nutrients over the
land, making the soil very fertile.
Wetlands and flood plains contain animal and plant life
specially adapted to deal with flooding. These areas also
act as flood defences, soaking up lots of water like a
sponge, which prevents flooding elsewhere.
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Human impact on flooding
Building roads and houses on flood
plains dramatically increases the
risk of flooding disasters. Water
simply runs off tarmac and concrete
and continues on its journey to more
populated areas, without being
absorbed into the ground.
Dams and flood defences also
disturb the natural flow of water.
Although dams offer protection to
some areas, they may inadvertently
cause flooding elsewhere.
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Blizzards
A blizzard is an extreme
winter storm, which is
characterized by strong
winds, decreased visibility,
freezing temperatures
and falling snow or ice.
The decreased visibility
in blizzards causes many
accidents. For anyone
trapped or injured in a
blizzard, the risk of
hypothermia is very severe.
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White-out
The most extreme form of
blizzard is known as a white-out.
This is when the snow is so
heavy that it becomes impossible
to distinguish the ground from the
air.
People easily become lost and
disorientated in these very
dangerous conditions.
Car accidents are common and
aeroplane pilots caught in these
conditions, may have difficulty in
keeping a steady altitude.
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Weather hazards bingo
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Key ideas
Hurricanes form out at sea, when warm ocean air rises
upwards to create a cycle of evaporation and condensation.
Tornados occur when warm fronts collide with cold fronts,
forming a vortex or funnel cloud which then hits the ground.
Heatwaves are when the temperature is unusually high over
an extended period for a certain region.
Forest fires are mainly caused by human activity but are also
caused by lightning. Drier conditions increase the risk of fire.
Droughts are extended periods when water availability falls
below the statistical requirements for a region.
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Key ideas
Lightning is an electrostatic discharge which occurs within
a cloud, or strikes from a cloud to the Earth.
Hail forms when ice crystals gather moisture and refreeze
over and over again, until heavy enough to fall to Earth.
Floods are an overflow of water that submerges land. They
vary in severity and may occur for many different reasons.
Blizzards are extreme winter storms, characterized by
strong winds, freezing temperatures and decreased visibility.
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