IB Notes

Hazards and disasters

HURRICANES

- Intense hazards that bring heavy rainfall (up to 500mm in 24 hours), strong winds (up to 250km/h) and high waves (3 - 5 meters).

- May cause hazards such as flooding, storm surges and mudslides.

- Tropical storms created 20 degrees north and south of the equator. Happens from summer to autumn.

- Last up to 10 days.

- Eye can be 100km wide, hurricane can be 800km wide, wind speeds can reach over 250km/h, can move at 50km/h.

- Eye has low pressure (as low as 880 millibars), clear skies (condensation is reduced), warm temp, calm.

- Vortex has dense cloud, violent wind, heavy rain.

 

- Moves excess heat from low lattitudes to higher lattitudes.

- Usually develop in westward-flowing air just north of the equator and creastes small-scale tropical depressions. 

- Localized areas of low pressure causes warm air to rise and may trigger thunderstorms.

- Only 10% of tropical disturbances become hurricanes.

 

CHARACTERISTICS

- Predictability: Can predict where they will happen but its route is erratic. Hard to predict their path so it is hard to give more than 12 hours of notice (insufficient for proper evacuation measures).

- Frequency: Frequent during summer and autumn.

- Spatial dispersion: In hot and dry areas. 

- Speed of onset: Days

- Duration: Days to weeks

- Areal extent: Local

 

FORMATION

- Characterized with large quantities of water. They originate over moist tropical seas. 

- Caused by sea water over 27°C to a depth of 60 meters (to give off enough heat energy).

-Low pressure winds must be at least 119 km/h. The area of low pressure must be far enough from the equator so the Coriolis force creates sufficient rotation of rising air mass.

- Conditions must be unstable.

 

- Sufficient amounts of warm water evaporates when the sea is over 27°C .

- Warm water must be over 60m deep as storms stir up the ocean, bringing up cold water from below.

- Winds come together and converge near the surface.

- Relative humidity  of over 60% to provide sufficient energy to power the hurricane.

- The air needs to be warm (to release large quantities of heat) and unstable so it will continue to rise.

- Air up to 5500m needs to be humid as it is pulled into the storm. Extra water vapour supplies more latent heat energy. 

- Pre-existing winds (not created by storm) should come from the same direction at the same speed so it doesn't rip the storm apart.

- An upper atmosphere high-pressure area helps pump away air rising in the storm.

- Develops when warm air rises and spirals rapidly around a calm central area known as the eye.

- Air descends from the top of the systen so it can be warmed and to hold more moisture. 

 

IMPACTS

- Recorded on Saffir-Simpson scale (5 categories), based on wind intensity.

- Unpredictability of hurricane paths makes the effective management of hurricanes difficult. They can suddenly change course.

- The strongest storms don't always cause the greatest damage. 

- The distribulation of the population throughout the Carribean islands increases the risk associated with hurricanes. 

- Hazard mitigation depends on the effectiveness of the human response to natural events. Includes urban planning laws, emergency planning, evacuation measures and relief operations (rehousing schemes, distribution of food aid and clean water).

- LEDCs lose more lives to natural hazards as a result of inadequate planning and preparation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VULNERABILITY

- Vulnerability is the conditions that increase the susceptibility of a community to a hazard or to the impacts of a hazard event.

- Risk = frequency/ magnitude of hazard x level of vulnerability
              capacity of population to cope

 

Factors affecting vulnerability:

- Population denisty

- Understanding of the area

- Public education

- Awareness of hazards

- The existence of an early-warning system

- Effectiveness of lines of communication

- Availability and readiness of emergency personnel

- Insurance cover

- Construction styles and building codes

- The nature of society

- Cultural factors

 

- Extreme events are not natural hazards if people and/ or propert are not at risk. Environmental hazard is when they are at risk. 

- Environmental hazards are caused by people's use of dangerous environments. Therefore, a natural hazards are not just the result of 'natural' events.

 

People live in dangerous areas because:

- Lack of knowledge

- Geographical immobility

- Tempting benefits: Live on river floodplains as the river provides water, silt and fertile soils with opportunities for transport and recreation. (However, too little water could lead to conflict, desertification or femine). Volcanic environments provide rich soils and minerals.

- Too optimistic

- Cities built up already: Can't just move the entire population elsewhere. There may also be economic prosperity.

- Over population: The poor live in undesired areas that may be dangerous because they do not have enough money to live in better areas.

 

Changing climates:

- People are causing an increase in air pollution, water pollution and acidification. 

- Increasingly dry years are turning large areas into deserts, especially if water is used wastefully. This leads to increased risk of wind and water erosion, resulting in further declines in productivity. 

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GLOBAL HAZARDS

- A hazard is a perceived natural event which has the potential to threaten both life and property whereas a disaster is the realization of a hazard when it has a significant impact on populations.

- One communy's devastation may seem trivial to another. Climatic, political, social and economic factors may influence the disaster impact.

- Frequency of hazards is increasing (global warmingg) , level of vulnerability is increasing (poverty) , ability to cope is decreasing.

- The bigger the magnitude, the less frequent the event. 

- Social effects: Deaths & injuries, destruction of families, pollution, disease & illness, evacuation & relocation, loss of jobs and livelihoods. 

- Economic effects: Damage to properties & businesses, infrastructure, agriculture. Loss of jobs & livelihoods, money from tourism. Cost of welfare schemes and increased insurance premiums.

- A risk assessor will highlight the likelihood of harm and damage from a given disaster and advise on the best methods of preperation.

 

PREDICTIONS

 

Hurricanes

- Hard to predict path so we can only forecast its path. 

- They move westwards (creating Easterly windes) towards the poles. Changes direction when they meet Westerly winds further North or South.

- Satellites can provide early warning.

- Reinforced aircrafts fitted with instruments can fly through and over hurricanes. 

- Weather radars can locate storms within 320km of the radar station. 

 

Tsunami

- Impossible to predict precisely where and when it will happen.

- Only can tell after it has started which gives a few hours early warning. Affected by shoreline morphology.

- Submarine volcanoes can be monitored to predict the risk of a tsunami. 

- Tsunami warning system comprises of many tidal and seismographic stations spread over the oceans. If water passes a critical threshold, a warning is sent to Honolulu. The earthquake centre will be plitted and its magnitude will be investigated. Satellites can help with this as well. 

 

Volcanoes

- State-of-theart volcano monitoring techniques and instruments can be used to record movements in the mantle and crust.

- Hazard zonation maps can be prepared and circulated.

- An alert and warning system can be used.

- Smoke from the vent, rumblings, and small-scale spewing of magma can be used as an early warning.

 

Earthquake

- Measurement of small-scale ground surface changes.

- Small-scale uplift of subsidence

- Ground tolt

- Changes in rock stress

- Microearthquake activity

- Anomalies in the earth's magnetic field

- Changes in radon gas concentration

- Changes in electrical resistivity of rocks

 

ADJUSTMENT AND RESPONSE TO HAZARDS

- Experience, level of wealth and personality affects how a person copes.

- People can do nothing, adjust, or leave.

- Adjustment depends in the type of hazard, risk of hazard, and costs lost.

- Modifying the hazard event, improved forecasting / warning, sharing the cost are ways of managing the consequences of a hazard.

- Risk assessment includes the analysis of climatological records to determine how often cyclones have struck, their intensities and locations. History of wind speeds, frequencies of flooding, height location or storm surges. Information about the last 50 - 100 years of cyclone activity.