Chapter 2; Global Hazard Trends

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Chapter 2; Global Hazard Trends

Magnitude and frequency.
Magnitude is the size of a natural hazard event and so represent the amount of work down (e.g. the energy given off during volcanic eruptions). Magnitude scales categorise events according to size/energy amd enable people to understand the processes and to model the likely impacts.Scales include:

  • hurricanes: Saffir - Simpson scale (1-5)
  • earthquakes: Richter scale (1 - 10)
  • tornadoes: TORRO
  • volcaninc eruptions: explosivity index 

Frequency is how often of an event of a certain magnitude occurs. Low magnitude events are likely to be more frequent than high magnitude events which have low frequency. 

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Chapter 2; Global Hazard Trends

El Nino Southern Oscillation
The pacific ocean contains amounts of circulating warm and cold water. El Nino and La Nina are changes in this circulation linked with changes in the atmospheric processes. 

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Chapter 2; Global Hazard Trends

El Nino
This affects the weather around the world and therefore is a context hazard. These events hapoen every 2 - 7 years and last 1 - 2 years. 

How El Nino contributes to a more hazardous world.
During an El Nino:

  • rainfall is reduced in southeast Asia, New Zealand, Australia and Indiam keading to drought, crop failure and wilfdires
  • heavy rain in California, Mexico and the coasts of Peru and Ecuadir often results in flooding and mudslides
  • tornadoes in the USA are reduced
  • there are more cyclones in Hawaii but fewer in North Australia
  • southern Africa may experience drought while there may be floods in East Africa 

During a La Nina:

  • rainfall is higher than normal in Indonesia and the Philippines and lower than normal on the west coast of South America 
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Chapter 2; Global Hazard Trends

During a La Nina (cont):

  • souther Africa and southeast Australia may experience floods
  • eastern Africa, California and South America may experience drought
  • there are more hurricanes in the Carriebean and USA 

Human factors in disasters

Rapid population growth. Growing world population means:

  • pressure on land which leads to people living in high risk areas, such as low lying flood prone land in Bangladesh
  • growing numbers of very elderly people
  • a growing proportion of the very young in developing countries who are also vulnerable in the even of a disaster

Deforestation and land degradation

  • deforeastion to gain farmland, which can cause flooding and soil erosion and contributes to climate change
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Chapter 2; Global Hazard Trends

  • destruction of mangroves as coastal areas are developed, which leads to coastal erosion and flooding


Rural-urban migration and rapid uncontrolled growth of cities lead to:

  • the development of squatter settlements on areas which are at high risk of flooding or landslides 

Poverty and politics

  • earthquakes have much higher death tolls in less developed countries which cannot afford the technology to build earthquake-proof building
  • developing countries may not be able to afford to prepare for emergencie
  • if populations are poorly educated and have little access to communications technology it is harder to prepare them for disaster
  • it is difficult to get aid to remote areas with poor infrastructure such as rooads and bridge
  • corrupt governments may misuse resourses, making disasters worse or prevent internationial aid reaching their populations (e,g, Myanmar (Burma) follwing the 2004 Asian tsunami 
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Chapter 2; Global Hazard Trends

Global disaster trends: a summary
Naturual disasters are more common in countries with a low and medium level of development. Many of these countries are in tropical areas which have monsoon rainfall or hurricanes.
Disasters cause more death and disruption in poor countries, which lack the resources and funds to develop high-tech prevention and prediction systems.
Damage in absolute economic terms remains highest in high-income countries, but in relative terms it is much mroe devasting for poorer countries. 

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