Global Hazards are the natural Phenomenon Everywhere, So learn about them

1. World at risk
Global hazards

2. Hazards and disasters (1)
• A natural hazard is a natural event with
the potential to harm people and their
property.
• A natural disaster is the realisation and
impacts of a natural hazard, I.e. the
deaths, injuries, disruption and damage.

3. Hazards and disasters (2)
The EM-DAT international database (
www.emdat.be/ ) suggests a hazard
becomes a disaster when at least one of the
following criteria are met:
• 10+ people are killed.
• 100+ people are affected.
• A state of emergency is declared.
• International assistance is called for.

4. Classifying natural hazards
Natural hazards can be classified by physical process.
Hydro-meteorological hazards result from weather systems.
Geophysical hazards result from tectonic processes.
Some hazards are termed context hazards because they have the potential to
affect the entire planet.
Global warming is a context hazard.

5. Depressions (1)
• Depressions, or mid-latitude cyclones, are cyclonic storms.
• They form when cool polar maritime (Pm) and warm tropical maritime (Tm) air
meet at the polar front.
• The less dense Tm air rises, forming clouds and precipitation along warm and
cold fronts.
• Depressions rotate around a low pressure centre.
• As they develop strong winds and heavy rain (or snow) intensify. Gale force
winds can cause property damage and floods may occur.
• In some cases, severe depressions produce significant hazards.

6. Depressions (2)
Weather associated with the passage of a depression

7. Hurricanes (1)
• Hurricanes are intense storms in the subtropics.
• They begin as tropical depressions and intensify into hurricanes.
• Hurricanes need sea surface temperatures of 27°C+ to generate intense
convection, plus weak upper level winds to allow the storm to develop its
characteristic spiral.
• Hurricanes form 500 km north and south of the equator where the Coriolis
effect is strong enough to generate spin.
• Hurricane strength is measured using the Saffir-Simpson scale ranging from
weak Category 1, to intense Category 5.
• Hurricane force winds, driving rain and storm surges batter coastlines as a
hurricane passes.

8. Hurricanes (2)
Cross-section of a hurricane

9. Drought
• Drought is a lack or shortage of water for an unusually long period of time. It
can take many months or even years to develop.
• Droughts hit hardest in areas which rely directly on agriculture, i.e. the
developing world.
• Eventually famine sets in as food supply runs out.
• This often leads to large-scale migration.

10. Floods
• Flooding occurs when the capacity of a river channel is exceeded by the water
discharge.
• Persistent rain, over a period of days or weeks, leads to more widespread
flooding.
• Widespread flooding tends to cause property damage as houses and fields
remain underwater for days or weeks.
• Flooding has complex causes, often partly human, e.g. deforestation and poor
river management.
• Flash floods often occur due to intense precipitation over a small area. These
sudden floods can have a devastating effect.

11. Tornadoes (1)
• Tornadoes are small-scale, short-lived storms. They remain in one place for
only a few seconds.
• They begin as large thunderstorms (supercells) where warm and cold air meet.
• Rapidly convecting warm air produces towering clouds which are twisted by
strong upper level jet stream winds.
• Winds can reach up to 350 km h–1
while the tornado itself moves at an average
of about 60 kmh–1
.
• Tornado wind speed is measured using the Fujita scale. An F5 tornado has
winds in excess of 323 km h–1
.
• Tornadoes can be locally devastating, ripping narrow paths of complete
destruction.

12. Tornadoes (2)
The structure of a tornado

13. Fire
• Wildfires are a natural phenomenon, often started by lightning.
• They are common during heatwaves and droughts when vegetation is especially
dry.
• Strong, dry winds such as the Santa Ana winds of California combined with
drought conditions can create ‘fire weather’, raising wildfire risk.
• Wildfires become extreme when the canopy (or crown) of trees catches fire.
Such fires can spread at incredible speed.
• The tendency for people to try to extinguish all forest fires can actually raise
risk. Unburned leaves, twigs and branches build up over time to create a vast
fuel source making fires more powerful.

14. Volcanoes (1)
• Volcanoes occur when magma is forced to the surface through cracks and
fissures in the Earth’s crust.
• The degree of volcanic hazard is measured using the VEI (volcanic explosivity
index) scale ranging from 0 to 8.
• Explosivity depends on magma viscosity. The more viscous the magma, the
more hazardous the volcano.
• Viscosity depends on temperature, gas and silica content.
• Highly explosive volcanoes erupt low temperature, viscous lava with a high silica
content.
• Volcanoes are often places of multiple hazards.

15. Volcanoes (2)
Cross-section of an erupting volcano

16. Earthquakes (1)
• Earthquakes most commonly occur when two tectonic plates move suddenly
against each other.
• Rocks fracture underground at the earthquake focus and the Earth’s crust
shakes as energy is released.
• Waves spread from the epicentre, the point on the surface above the focus.
• Earthquakes are measured using the Richter magnitude scale, and Mercalli
intensity scale.
• Severe earthquake damage can occur when unconsolidated sediment undergoes
a process called liquefaction. This is often responsible for the worst ground
shaking and damage.

17. Earthquakes (2)
Cross-section across oceanic/continental plate
convergence at a destructive plate boundary

18. Tsunamis (1)
• Tsunami waves are caused by the rapid displacement of water.
• Submarine earthquakes are the most common cause.
• Across the open ocean tsunami waves travel at speeds up to 700 km h–1
. The
wavelengths are hundreds of kilometres, but their height is only about 1 m.
• Tsunami waves cannot be seen out at sea. Only as they approach the shore,
slow down and increase in height does their potential for destruction become
clear.

19. Tsunamis (2)
How a tsunami is generated

20. Tsunamis (3)
How a tsunami is generated

21. Tsunamis (4)
How a tsunami is generated

22. Landslides
• Landslides are down slope movements of rock and soil under the influence of
gravity. They are part of a wider group of processes termed mass movement.
• The term ‘landslide’ implies a relatively rapid movement, ranging from seconds
to a few days.
• Most hazardous landslides involve water, and heavy rain is often one of the key
causes. Earthquakes often trigger landslides too.
• Rapid liquid flows (e.g. mud and debris flows, volcanic ash lahars) are the most
devastating.
• Like floods, landslides often have complex causes and humans frequently play a
part, e.g. increasing risk due to deforestation.

23. Avalanches
• Avalanches are a type of mass movement which involves snow, ice and other
debris.
• They occur on mountains, typically on slopes of about 30°–45°.
• Avalanches occur within snowpacks which contain different layers of snow,
some weak and some strong.
• Changing wind conditions, temperatures and further snow falls can cause weak
snow layers to fail. Human actions (e.g.skiing) and other triggers (e.g.Earth
tremors) also contribute.
• Failure is often in the form of slab failure, when a large area of snow begins to
move. Speeds of 300 km h–1
can be reached as the slab breaks up and rushes
downslope.
• Most avalanche fatalities result from burial.

24. Risk (1)
• Risk, as shown in the disaster risk
equation, increases as hazardous
events become more common,
people become more vulnerable and
their capacity to cope decreases.
• Risk can be reduced by reducing
vulnerability, increasing capacity or
reducing hazard frequency and/or
magnitude.
R = risk, H = frequency or magnitude of hazard,
V = vulnerability level, C = capacity to cope

25. Risk (2)
Risk The probability of harmful consequences, or expected losses, resulting from
interactions between natural or human-induced hazards and vulnerable conditions.
Hazard A potentially damaging physical event, phenomenon or human activity that
may cause the loss of life or injury, property damage, social and economic disruption
or environmental degradation.
Vulnerability The conditions determined by physical, social, economic and
environmental factors or processes, which increase the susceptibility of a community
to the impact of hazards.
Capacity to cope A combination of all the strengths and resources available within
a community, society or organization that can reduce the level of risk, or the effects
of a disaster.

26. Vulnerability (1)
• Vulnerability is important because it helps to determine the exact impact a
hazard will have on a population.
• In general, developing countries and regions are more vulnerable than
developed ones.
• Capacity to cope is generally lower in the developing world, so hazard impact
lasts longer than in the developed world.
• Vulnerability has social, economic, environmental and physical aspects.
• Poverty, poor social conditions, environmental degradation and unfavourable
physical geography all increase vulnerability.

27. Vulnerability (2)
Increasing vulnerability
• Population growth
• Urbanization and urban sprawl
• Environmental degradation
• Loss of community memory about
hazards
• Ageing population
• Ageing infrastructure
• Greater reliance on power, water,
communication systems
• Over-reliance on technological fix
Decreasing vulnerability
• Warning and emergency-response
systems
• Economic wealth
• Government disaster-assistance
programmes
• Insurance
• Community initiatives
• Scientific understanding
• Hazard engineering

28. Vulnerability compared
Bam, Iran
December 2003
6.6 Richter scale earthquake
Hawaii, USA
October 2006
6.7 Richter scale earthquake
Deaths/
injuries
At least 25,000 deaths/around
30,000 injured
0 deaths/several hundred minor
injuries
Property
damage
Economic losses about $10 billion;
up to 90,000 people displaced;
18,000 buildings destroyed
$73 million in damage, including
1,200 buildings damaged
• In Bam 90% of buildings were mud (adobe) brick built, with no structural frame. In Hawaii,
most buildings could resist the ground shaking with only minor damage.
• In Bam, many emergency service buildings and vehicles were damaged by the earthquake.
• Average incomes in Hawaii are $30,000 per year compared to $3,900 in Iran. Bam is in one
of Iran’s poorer, more isolated regions.

29. Global warming: a context hazard (1)
• Global warming is described as a chronic hazard because it is continually present.
• Other context hazards, eg. an asteroid strike or super-volcanic eruption, are
described as rare because they are ‘one offs’.
• Global warming is potentially a global hazard because its impacts could be very
widespread, e.g causing whole climate zones to shift .
• Global warming could cause increases in the frequency and magnitude of hydro-
meteorological hazards (see next slide).
• It could also increase vulnerability to tectonic hazards by reducing food supply and
water availability.
• It might be argued that global warming is unjust, as approximately 80% of pollution
is caused by the developed world but it is likely to be the more vulnerable developing
world which is most at risk as climates change.
• As a global problem, it requires a global solution which is by its very nature,
complex.

30. Global warming: a context hazard (2)
Floods Changing rainfall patterns could increase risk in some areas; floods
may become more common.
Drought Already vulnerable areas such as the Sahel could experience
increased drought.
Avalanches Mountain areas could experience more variable weather patterns,
reducing predictive ability.
Hurricanes These may become more intense, and possibly more frequent. New
areas could become affected.
Depressions These could become more frequent, and more intense over areas
such as the UK.
Possible impacts of global warming on hydro-meteorological hazards