Natural Hazards

HO Pui-sing

Contents

What are natural hazardsFloodingDrought

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 resourcesGeomorphic: flat plains and othersLocational: good location for transport, communic

ation 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 hazardsGeophysical Biological

Meteorological 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 areMagnitudeSpeed of onsetDurationFrequencyAreal extentAreal reliability

Six IndicatorsMagnitude

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 onsetIt 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

yearsFloods: days or weeksTornados: minutes or

hours

FrequencyIt 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 na

rrow belt of the landscape.

Drought or flood: several thousand km.

Areal reliabilityPredictability of an natur

al hazards occur in an given area.

Predictable and possible for planning.

Example:Volcanic eruptions: fixed

point (volcano)Floods: channels and flo

od plainsTropical cyclones: sever

al erratic pathsEarthquakes: unknown

Hazards Profile

Impacts of natural hazards and level of economic development

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

Bangladesh (1970) vs United States (1969)

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 and relative wealth, whereas they are increasingly costly in absolute wealth in industrial nations."

Flooding

What is FloodingNature of floodCasuses of floodsImpacts of floodsPeople’s responses to floodsPrevention of floods

What is Flooding?Flood:

Coastal flooding: (above average sea level)Unusual atmospheric conditions (eg. Onshore hurr

icane, tornado…)Earthquake or volcanic eruption that set up huge ti

dal surges.River flooding (flow exceeds bank-full capacit

y)It is a common hazard and occur anywhere in a riv

er channel at lower courseMay be caused by

Heavy rainRapidly melting snowNatural or man-made dams collapseothers

Nature of floodFloods are the most common of all natural hazards

Covers the largest spatial areaCauses the greatest loss of life and propertyHuman beings settle on flood plains

Abundant water supplyFertile soil for farmingFlat relief for developmentNavigator (transportation)

Damage of floodsWater 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 FloodsNatural 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

No vegetation cover in highland

Few lakes

Poor mining method to enhance the land sinks

Poor management of embankments

Impacts of floodsDate Place Deaths Property Damage

1968 Gujarat, India 1000  

1963 Belluno, Italy > 2000 Vaiont dam overtopped

1955 Pakistan and India 1700 2.27 million crop ha at loss of $63 million

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

Impacts of Floods – cont’dWhat 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 responsesPerceptions

How people will interpret various hazardsA range of responses

Accepting the hazards – Act of GodTrying to predict Taking appropriate action to reduce damage

potentialTo offsetting the losses through insurance

People’s perceptionHazard Perception Common Responses

1. Deny the hazard exists at all Do notingeg. '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 and inevitable event

Do nothingeg. 'We get floods here every five years' Prayeg. 'It's all in the hands of God.'

3. Hazards are inevitable, but controllable.

Modify the causes of floodingeg. forest planting in catchment areas to absorb runoff

People’s perception – cont’d4. Hazards are inevitable, but the effects can be controlled

Reduce the damage potentialeg. warning systems; community awareness programmes; evacuation procedures; special building designs; low intensity land use zoning on flood plainsLeave the area:eg. seasonal nomadism; move in with friends or family; permanent migration.Plan for the damage and losseseg. flood insuranceSpread the losses across the communityeg. disaster relief funds; government subsidized insurance; international emergency reliefBear the losseseg. use savings

5. Some hazards are made or intensified by people

Alter human behaviour and land use patternseg. 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 economic factors that force the poorest people to live in flood-prone areas.

People’s perception – cont’dPerception 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 communityWealth and economic developmentCommunity awareness and preparationsWillingness of local and national government to spend

money onLong-term hazard prevention and damage reduction schemes, orShort-term emergency relief after a disaster

People’s perception – cont’dThese factors emphasized the social or cultur

al 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.

Bounded rationality vs Satisfying behaviour

People’s perception – cont’dBounded rationality

People like to make a rational choice of responses.

However, Few people have access to

full informationMany are just not aware of

all the alternative responses available

People differ in their abilityFew like to forget previous

painful history

Satisfying behaviourPeople make choices th

at help them achieve a satisfactory level of reward, but

Stop short of striving for the highest possible level.

SatisficerAccept ‘tolerable’ levels

of hazardAvoid the worst of the im

pactTheir property is insured

anyway.

People’s ChoicesOnly those people have a range of choices of

response to hazardsAccess to full information.Strong networked of familyStrong friendship supportStrong wealth and political power

Prevention of floods

Flood management strategiesMethods of floods prevention

BehaviouralStructural

Example

Flood management strategiesIndividual 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 s

imilar to compulsory third party car insurance. 6. Government support for local council flood control p

rojects, surveys, and engineering works.

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 12. Funding to support relocations and flood-proofing as

alternatives to repetitive rebuilding.

Management Strategy

Local Council National Government

Prediction3, 4, 8, 10

  

3, 4, 8

Hazard prevention2, 6, 8

  

6, 8

Impact Reduction1, 5, 7, 9, 10

  

1, 5, 7

Relief and Reconstruction

11, 12  

11, 12

Methods of floods preventionBehavioural

Accepting loss (Third World)

Public relief fundsFlood insuranceFlood forecasting an

d warning

StructuralReserviors (dams buildi

ng)Channel enlargementChannel straighteningEmbankmentsFlood relief channelsBarragesFlood plain zoningReforestation

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

hazardPeople’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 lifeCrops and livestockNatural vegetation and wildlifeSoilPopulation 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 EffectsPopulation growth has put increasing pressure

on the environment.This pressure increases the risk of human-

induced 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.