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Natural Hazards. Chapter 4. Natural Hazard. What is a Natural hazard? Why should we study it? Natural events causing great loss of life or property damage 2004: Asian Tsunami: >200,000 1970: Bangladesh Cyclone: 300,000 1976: China earthquake: 300,000 Different types of Natural Hazards:

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Natural hazards l.jpg

Natural Hazards

Chapter 4


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Natural Hazard

  • What is a Natural hazard? Why should we study it?

    • Natural events causing great loss of life or property damage

      • 2004: Asian Tsunami: >200,000

      • 1970: Bangladesh Cyclone: 300,000

      • 1976: China earthquake: 300,000

  • Different types of Natural Hazards:

    • Volcanism, earthquakes, Hurricane, tornado, Tsunami, Flooding, Landslides

  • Damages from different types of Natural Hazards

  • Magnitude, frequency, catastrophe

    • Impact of a disaster is related to magnitude (how big) and frequency (how often). These two are inversely related. Actual damage depends on other factors too, such as population, climate, landuse, geology etc etc.

    • Catastrophe: immense damage: recovery and rehabilitation is a long invloved process



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Benefits of Natural hazards

  • Flooding :

    • deposits fertile sediments in floodplains

    • Nourishes beaches

  • Volcano:

    • Adds landmass e.g., in Hawaii

    • Produces fertile soil

    • Created the atmosphere and hydrosphere


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Evaluating Hazards

  • Fundamental Principles:

    • Hazards are repetitive and predictable

    • Risk Analysis is important for understanding impact

    • Hazards are linked, e.g., volcano, earthquake, tsunami, landslide, flooding, forest fire..

    • Human interference is magnifying damage

    • Consequences can be minimized


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Disaster Prediction

  • Location:

    • e.g., Volcanoes and earthquakes along plate boundaries

  • Probability of occurrence

    • Hazards are cyclical,

    • With sufficient data probability of occurrence can be calculated

  • Precursor events

    • Volcanoes, earthquakes, landslide, flooding..often associated with precursor events

  • Forecasting

    • Is possible by monitoring hazards e.g., hurricanes, tsunamis, volcanic eruption etc

  • Warning

    • Should be issued even at the risk of the hazard not materializing


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Risk Assesment

  • Risk Determination

    • Risk= probability X damage

  • Acceptable Risk

    • Risk-tolerance level of the society

    • Can vary: High for automobiles but low for nuclear accident

  • Problem and opportunities

    • Lack of long term data– how do we calculate risk?

    • Information may be complex and difficult to analyze e.g., what is the effect of radiation leak from a nuclear reactor?

    • Better risk assessment will lead to better decisions


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Human Response to hazards

  • Reactive – traditional response

    • Impact

      • Direct (People killed, property damaged – affects individuals or small groups) and

      • Indirect effects (mental trauma, tax, donations—affects population)

    • Stages:

      • Emergency: Search and Rescue, shelter, opening roads

      • Restoration: water and power, return to home, cleaning of rubble

      • Reconstruction I: Return to pre-disaster level

      • Reconstruction II: improvement

    • Rapid Restoration can be counter-productive

  • Anticipatory – a better way to reduce damage

    • Hazard perception by people and by government

    • Land-use planning: avoid hazardous locations

    • Insurance: often not extended to high risk areas

    • Evacuation

    • Disaster preparedness

  • Artificial control

    • Difficult, expensive and often cause more harm

      • Channelization of Kissimmee river

      • Sea walls, dams…


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Future trends

  • Global Climate and hazard

    • Global warming is increasing weather related disasters

  • Population and hazard

    • Greater population density leads to higher risk

    • Change in land-use pattern magnifies damages

      • Recent floods in Haiti related to deforestation


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. Global climate and hazards

  • A. Global and regional climate change may significantly affect incidence of storms, landslides, drought, fires

    • 1. how climate change may affect magnitude and frequency of natural events

      • a. sea level rise may increase coastal erosion

      • b. shift in food production areas

      • c. expansion of deserts and semi-deserts

    • 2. warming of oceans will channel more energy from ocean water into atmosphere

      • likely will increase hazardous weather-related processes


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Population increase, land-use change, and natural hazards

  • A. Population increase and hazardous events

    • 1. as population increases, need for planning to minimize losses from natural disasters also increases

      • a. more people at risk of an event

      • b. forces more people into hazardous areas

  • B. Land-use change and hazardous events

    • 1. past half-century has seen dramatic increase in great catastrophes

    • 2. vast majority of natural disaster deaths between 1985-1995 were in developing world

      • a. Hurricane Mitch: hillsides stripped because of heavy rains on cleared and burned land

      • b. Yangtze River: timber harvest and conversion to agriculture has increased flood hazard