Natural Hazards HO Puising Contents What are natural
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Natural Hazards HO Pui-sing
Contents ©What are natural hazards ©Flooding ©Drought
Natural environment ©Natural environment has provided man with useful resources. ©Natural environment may be classified into four categories: ©Physical: energy, mineral and soil resources; ©Biotic: forest, fish, animal and other life resources ©Geomorphic: flat plains and others ©Locational: good location for transport, communication and defence.
What are Natural Hazards © The natural environment is unstable. © People have been learning to deal with the environmental risks and changes produced by the unstable environment. © Extreme natural process (flood, earthquake or landslide…. . )has the potential to be a natural hazard if it occurs where people live or have their property (buildings or animals…). © Natural disaster when it exceeds normal expectations of frequency or involved.
Venn Diagram of Natural Hazards and Natural Disasters© Responding to those hazards, society may seek to modify the natural events system and the human use system of locations, livelihoods, and social organization.
Classification of hazards Geophysical Meteorological Biological Geomorphic Floral Faunal Blizzard and snow Avalanche – rock Fungal disease Bacterial, viral and protozoal disease Cold wave Avalanche – snow Hay fever Malaria Drought Earthquake Infestation Foot and mouth disease Flood Erosion Weeds Infestation Fog Expansive soil Red tide Rabbits Frost Landslide Locusts Hailstorm Shifting sand Grasshoppers Heat wave Tsunami Lightning strike and fire Volcanic eruption Temperature inversion Tornado Tropical Cyclone Windstorm
Measuring and analyzing natural hazards ©Six indicators to measure and analyze the extreme geophysical events that comprise natural hazards. They are ©Magnitude ©Speed of onset ©Duration ©Frequency ©Areal extent ©Areal reliability
Six Indicators © Magnitude ©It is the most important indicator. ©Magnitude rate as ‘extreme’ happenings and pose sufficient threats to the human system to be considered natural hazards. ©Example: ©The Richter Scale © Speed of onset ©It refers to the length of time between the first appearance or warning of an event and its peak. ©Example: ©Slow-onset hazards (drought and soil erosion) ©Rapid-onset hazards (floods and earthquakes)
Six Indicators – (cont’d) © Duration ©It refers to the period of time over which it occurs. ©Example: ©Droughts: seasons or years ©Floods: days or weeks ©Tornados: minutes or hours © Frequency ©It refers to how often an event of a given magnitude may be expected to re-occur. ©‘Return period’: a recurrence interval of 10 years is to say it has in any year a 10% chance of occurring.
Six Indicators – (cont’d) © Areal extent ©The area of natural hazards affect. ©Example: ©Avalanche: short and narrow belt of the landscape. ©Drought or flood: several thousand km. © Areal reliability ©Predictability of an natural hazards occur in an given area. ©Predictable and possible for planning. ©Example: ©Volcanic eruptions: fixed point (volcano) ©Floods: channels and flood plains ©Tropical cyclones:
Hazards Profile
Impacts of natural hazards and level of economic development Bangladesh (1970) vs United States (1969) Tropical cyclone GNP per capita ($US) Population affected (millions) Lives lost Estimated value of damage ($US) Type of damage suffered Unnamed, Bangladesh 12 -13 November 1970 1971: $90 1980: $130 4. 7 30000 $64 million Loss of crops, especially rice; loss of cattle; 400, 000 peasant houses damaged or destroyed; small fishing boats destroyed; trees down Gamille USA 17 -20 August 1969 1971: $5000 1980: $11360 19 256 $1422 million Houses destroyed or damaged; shipping damaged or destroyed (both fishing and cargo); shopping centers severely damaged; highways and railroads damaged; telephone cables down; cars and lorries damaged; trucking terminal destroyed; oil rigs damaged; loss of cattle and ruin of crop land; schools and colleges damaged; community buildings damaged; cinemas and entertainment centers damaged
Impacts of natural hazards and level of economic development © " About 95% of disaster related deaths occur among the two thirds of the world's population that occupy developing countries. In contrast to (these). . . differences in death rate, economic loss from natural disaster is commensurate with income distribution. About three-quarters of absolute global loss occurs in the wealthy countries. . . (However) the ratio of loss to income is much higher in the developing countries. . . In developing countries, disasters may be less frequent but are more catastrophic and more costly in lives
Flooding ©What is Flooding ©Nature of flood ©Casuses of floods ©Impacts of floods ©People’s responses to floods ©Prevention of floods
What is Flooding? ©Flood: ©Coastal flooding: (above average sea level) ©Unusual atmospheric conditions (eg. Onshore hurricane, tornado…) ©Earthquake or volcanic eruption that set up huge tidal surges. ©River flooding (flow exceeds bank-full capacity) ©It is a common hazard and occur anywhere in a river channel at lower course ©May be caused by ©Heavy rain ©Rapidly melting snow ©Natural or man-made dams collapse
Nature of flood © Floods are the most common of all natural hazards ©Covers the largest spatial area ©Causes the greatest loss of life and property ©Human beings settle on flood plains ©Abundant water supply ©Fertile soil for farming ©Flat relief for development ©Navigator (transportation) ©Damage of floods ©Water inundating (flooding) land, utilities, buildings, crops, communication and transport facilities. ©After flooding, debris block streets, reservoirs and cover fields. ©Disrupt normal supply of water, food, shelter and medicine, which cause health and pollution problems.
Causes of Floods Natural Man-made Many tributaries Poor farming methods Flood plain Over grazing Snow melting Cut ditches to improve the drainage of their moorland Heavy rain storms Erosion of peat The land sinking / Sea level rising Few lakes No vegetation cover in highland Poor mining method to enhance the land sinks Poor management of embankments
Impacts of floods Date Place Deaths Property Damage 1968 Gujarat, India 1000 1963 Belluno, Italy > 2000 1955 Pakistan and India 1954 Kavin, Iran > 2000 1953 Northern Europe > 2000 1951 Northern China > 5000 1939 Tianjin, China 1000 Million homeless 1933 Huang He, China 18000 3. 6 million affected 1911 Chang Jiang, China 100000 1887 Henan, China 900000 Huang he overflowed, communities destroyed 1642 Huang He, China 340000 Kaifeng city was completely destroyed 1700 Vaiont dam overtopped 2. 27 million crop ha at loss of $63 million
Impacts of Floods – cont’d What were the impacts of floods on people and the environment? 1. Loss of life and homeless 2. Crops damaged and loss of livestock 3. Disrupting transport system / network 4. Fertile soil wash away from farmland (soil erosion) 5. Rivers become shallow due to soil deposition (not suitable for navigation) 6. Reduce storage capacity of reservoirs
People’s responses ©Perceptions ©How people will interpret various hazards ©A range of responses ©Accepting the hazards – Act of God ©Trying to predict ©Taking appropriate action to reduce damage potential ©To offsetting the losses through insurance
People’s perception Hazard Perception Common Responses 1. Deny the hazard exists at all Do noting eg. 'It can't happen here. ' 'I know it flooded here 20 year ago, but lightning never strikes in the same place twice. ' 2. Accept the hazard as a natural Do nothing and inevitable event eg. 'We get floods here every five years' Pray eg. 'It's all in the hands of God. ' 3. Hazards are inevitable, but controllable. Modify the causes of flooding eg. forest planting in catchment areas to absorb runoff
People’s perception – cont’d 4. Hazards are inevitable, but the effects can be controlled Reduce the damage potential eg. warning systems; community awareness programmes; evacuation procedures; special building designs; low intensity land use zoning on flood plains Leave the area: eg. seasonal nomadism; move in with friends or family; permanent migration. Plan for the damage and losses eg. flood insurance Spread the losses across the community eg. disaster relief funds; government subsidized insurance; international emergency relief Bear the losses eg. use savings 5. Some hazards are made or intensified by people Alter human behaviour and land use patterns eg. reduce stocking levels; introduce low intensity land use zoning and bans on living in flood-prone areas; stop dredging that interferes with the river channel pattern; after political, social and
People’s perception – cont’d © Perception is influenced by the following: ©The past record of hazards (magnitude and frequency) ©The strength of traditional cultures (attitudes to the environment) ©Education standard of the community ©Wealth and economic development ©Community awareness and preparations ©Willingness of local and national government to spend money on ©Long-term hazard prevention and damage reduction schemes, or ©Short-term emergency relief after a disaster
People’s perception – cont’d ©These factors emphasized the social or cultural framework in which people live. ©In fact, the range of choices open to people is very limited and controlled by the social, economic and political conditions and pressures. ©From this perspective, it can explain why people often do seemingly irrational things.
People’s perception – cont’d © Bounded rationality © Satisfying behaviour ©People like to make a rational choice of responses. ©However, ©Few people have access to full information ©Many are just not aware of all the alternative responses available ©People differ in their ability ©Few like to forget previous painful ©People make choices that help them achieve a satisfactory level of reward, but ©Stop short of striving for the highest possible level. ©Satisficer ©Accept ‘tolerable’ levels of hazard ©Avoid the worst of the impact
People’s Choices © Only those people have a range of choices of response to hazards ©Access to full information. ©Strong networked of family ©Strong friendship support ©Strong wealth and political power
Prevention of floods ©Flood management strategies ©Methods of floods prevention ©Behavioural ©Structural ©Example
Flood management strategies © Individual can do little on the manage the impact of hazards except personal preparations and insurance. © Flood management should be a collective action and ought to be coordinated by government (local and national) ©Most governments only provide emergency relief and reconstruction after the hazards for facing many conflicting demands on the public purse with limited resources. ©Economically richer nations, governments have adopted a range of actions to predict, prevent or minimize the effects of hazards and providing disaster relief and reconstruction.
Twelve actions to manage the hazards © 1. Subsidized flood insurance for farmers and industrialist © 2. Use of existing government laws to ensure local planners take proper and consistent account of flood hazards. © 3. Development of a uniform method of determining flood frequency. © 4. An improved system of flood forecasting. © 5. Compulsory household flood insurance scheme similar to compulsory third party car insurance. © 6. Government support for local council flood control projects, surveys, and engineering
Twelve actions to manage the hazards – cont’d © 7. Community education programmes to disseminate flood hazard information and alternative methods of reducing flood losses. © 8. Research to delimit major flood areas and to provide flood hazard information in the form of maps, chart, graphs and narrative descriptions. © 9. Use of zoning regulations to locate low intensity land uses in flood-prone areas. © 10. Development of flood warning system, based upon agreed lines of responsibility and communication, using established flood heights as the determinants of action. © 11. Funding of local emergency relief services
Management Strategy Prediction Hazard prevention Impact Reduction Relief and Reconstruction Local Council 3, 4, 8, 10 2, 6, 8 1, 5, 7, 9, 10 11, 12 National Government 3, 4, 8 6, 8 1, 5, 7 11, 12
Methods of floods prevention © Behavioural ©Accepting loss (Third World) ©Public relief funds ©Flood insurance ©Flood forecasting and warning © Structural ©Reserviors (dams building) ©Channel enlargement ©Channel straightening ©Embankments ©Flood relief channels ©Barrages ©Flood plain zoning ©Reforestation
Case Study: Thames flood barrier scheme © Location: Central London © Painful events: 1928 (14 people died), 1953 (300 people died) © Reasons: © Southern Britain is slowly sinking © Very slow rise in world sea level © Special weather conditions (north-easterly winds from North Sea make a surge to London) © Time: October to March (high tides and surges of water)
Case Study: Thames flood barrier scheme © Scheme: completed in 1982 © Location: River Thames at Woolwich © Construction: © Four main gates which can swing up from the river bed to form a continuous steel wall against the incoming flood. © The gates lie on the river bed when not in use for ships sailing up and down river. © River banks were also raised and strengthened. © Warming system: © 4 hours before flooding is expected, announcements will be made on TV and radio. © 1 hour to London’s flood, sirens will be sounded in riverside areas, and © Police will warn people with loud hailers to go to safety places.
Thames barriers
Thames barriers
Thames barriers
Thames barriers
Drought ©What is drought? ©Problems presented to man. ©Role of man in causing the drought hazard ©People’s perception and responses to drought
What is drought? © More than 1/3 of land is dry or very dry. © Desert: annual rainfall < 250 mm © Definition of Drought: © “a period of unusually or unexpectedly low rainfall, which upsets the ecological balance. ” © A condition in which the amount of water needed for transpiration and direct evaporation exceeds the amount available in the soil. © In term of the water need of a particular crop growing under a specific combination of environmental conditions. © Three classes of drought can be identified: © Permanent drought associated with arid climate. © Seasonal drought: annual periods of dry weather © Drought due to precipitation variability or unreliable
Problems to man ©Effects of droughts: ©People themselves and their way of life ©Crops and livestock ©Natural vegetation and wildlife ©Soil ©Population size and population redistribution
Role of man in causing the drought hazard © The human context in which hazards offer is more important than the geophysical causes of the event. © Some factors influencing the human impact of natural hazards © Population density in the area affected, © Prior experiences of hazards in the area, © Traditional methods of coping with hazards © The degree of accuracy in predicting the hazards, © The effects of any warning, preparation and /or evacuation procedures, © The speed and effectiveness of local, national and international emergency and long-term relief services, © The overall level of economic development in the area affected
Population Growth Effects © Population growth has put increasing pressure on the environment. © This pressure increases the risk of humaninduced hazards and disasters. © For examples ©The hazard of affecting the balance of world climates by extensive clearance of forest. (Amazon) ©The hazards of disturbing natural ecosystems and food webs by the clearance of vegetation, the use of chemicals in the atmosphere, and pollution. ©The hazard of increasing the risk of drought, floods and soil erosion by farming marginal areas particularly in semi-arid regions.
People’s perception and responses to drought Governments’ View Nomads’ View 1. The nomads just wander aimlessly in a never-ending search for pasture 1. We follow traditional routes that make the best use of a risky environment. 2. We must limit this needless movement so we can collect taxes and use their labour. 2. We must be able to move freely as our routes change according to climatic conditions. 3. We could encourage the nomads to raise herds for profit and benefit ourselves from trading with them. 3. We are not interested in selling our animals. They provide all our needs and are a sign of wealth. A Major Drought Occurs 4. The loss of human and animal life is shocking. We must solve the problem of drought. 4. Droughts and famines have always happened. We accept them as part of the risks we face. 5. We can use our superior technology to overcome the shortage of water. 5. The new water supplies are much more reliable and convenient. We must change our routes. 6. The nomads’ herds are very unhealthy and prone to disease. We can improve their quality. 6. The new medicines will protect our animals. Now we can own more because fewer will die from disease. Overgrazing and Climatic Change lead to increasing Desertification 7. The nomads herds are too large for the pastures available. We must reduce them. 7. The pastures are getting worse. We must keep as many animals as possible to allow for those that die. Major Drought 1968 -73 8. The nomads are to blame for the advancing desert. They must be settled permanently. 8. Conditions in our traditional lands are hopeless. We must find better pastures. 9. Now that the nomads are helpless we can make sure that they do not go back to their old ways. 9. Our herds have been destroyed. We have no option but to get food in the relief camps.
People’s perception and responses to drought Governments’ Action Nomads’ Action Large-scale vaccination programmes are carried out They fall back on traditional methods of surviving the drought Ways of improving the natural water supply are investigated. They move to relief camps makes them dependent on food Nomads are persuaded to become settled farmers when crisis is over. The size of their herds increases, causing overgrazing Attempts are made to control nomads. No changes are made in their traditional lifestyle. Nomadic tribes are ignored by early colonists. Fewer animals than usual are sold Deep wells and storage tanks are dug Herds are concentrated on new wells, causing overgrazing on surrounding land. Territorial frontiers established by colonists. Moving several hundred km further south, they clash with permanent farmers. Attempts are made by colonist to set up livestock markets. Nomads are offered high prices to encourage them to sell animals. Only a few animals are sold, usually the worst. They become aggressive over loss of land.
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