Natural Hazards and Disasters | CBSE Class 11 Geography Notes

This note covers natural hazards and disasters, human influences on vulnerability, earthquakes, tsunamis, tropical cyclones, floods, droughts, landslides, their distribution in India, their consequences, and measures for disaster preparedness, mitigation, rescue, relief and recovery.

How does a natural hazard differ from a disaster?

Changes in nature differ in speed, scale and intensity. The development of landforms may be gradual, while earthquakes and volcanic eruptions are sudden. From nature's perspective, changes are value-neutral, meaning neither good nor bad. People judge them by their effects on human life.

Definition: A natural hazard is an element or circumstance in the natural environment with the potential to harm people, property or both. A natural disaster involves relatively sudden, widespread death, property loss and disruption of social systems over which people have little or no control.

Ocean currents, steep slopes, unstable Himalayan structures and extreme conditions in deserts or glaciated areas can present hazards. A hazard becomes a disaster when the destruction and damage are very large. All hazards need not turn into disasters.

Why does the affected community matter?

A disaster causes or threatens serious disruption and requires efforts beyond those normally provided by emergency services. Vulnerability means susceptibility to harm from a hazard. The same broad kind of event can have different consequences in different social and environmental settings.

Every disaster is unique in its local conditions, the response it generates and the way different social groups deal with it. Population concentration and activities in exposed places help explain why a natural event can become a severe human calamity.

Mitigation means reducing adverse effects, while preparedness means planning and getting ready to respond. Since very little is possible to prevent natural disasters, reducing losses and improving the ability to respond are central tasks. Prevention of an event and reduction of its damage are different objectives.

How are disasters classified, and how do people increase their severity?

Natural disasters can broadly be grouped into four categories. This classification helps identify the nature of a threat and organise measures to deal with it promptly. It does not imply that the effects of a disaster remain confined to a single part of the environment.

What are direct and indirect human contributions?

Human-made disasters arise from human actions. The Bhopal gas tragedy, Chernobyl nuclear disaster and wars are examples. Pollution of air, water and soil also illustrates how human activity can cause damaging environmental change.

Other actions indirectly intensify disasters. Deforestation, unscientific land use and construction in fragile areas can aggravate floods and landslides. Greater technological capacity has enabled people to intensify activities in disaster-prone areas, increasing their vulnerability.

Settlement on flood plains, the low-lying land beside rivers that floodwater can cover, exposes people and property to flooding. Coastal growth in cities such as Mumbai and Chennai increases exposure to cyclones and tsunamis, especially where development extends to the shore.

India's geographical diversity, large population, prolonged colonial past and continuing social discrimination have enhanced its vulnerability. Understanding a disaster therefore requires attention to both the physical event and the social conditions in which it occurs.

Why do earthquakes occur, and which Indian regions are vulnerable?

Earthquakes involve earth movements associated with a sudden release of energy. Earthquakes of tectonic origin, arising from forces within the earth that alter landforms, have proved the most devastating and have a large area of influence.

Earthquakes linked to volcanic eruptions, rock falls, landslides, mining-related subsidence, or the impounding of water in dams and reservoirs have a more limited area of influence and scale of damage. Subsidence means sinking of the ground.

How does energy accumulate along the Himalayas?

1. The Indian plate moves towards the north and northeast at one centimetre per year.
2. The Eurasian plate obstructs this movement from the north, and the plates become locked.
3. Energy accumulates, producing increasing stress at the locked boundary.
4. The lock eventually breaks, and the sudden release of energy causes earthquakes along the Himalayan arch.

Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, the Darjeeling subdivision of West Bengal and the seven northeastern states are among the most vulnerable regions. Earthquake risk is not confined to the Himalayan belt.

Case study: What do peninsular earthquakes show?

Gujarat experienced severe earthquakes in 1819, 1956 and 2001, and Maharashtra in 1967 and 1993. Their occurrence in the old, stable Peninsular block was difficult for earth scientists to explain for a long time.

Some earth scientists have proposed a theory involving a fault line represented by the Bhima River near Latur and Osmanabad, energy accumulation along it, and the possible breaking down of the Indian plate. A fault is a fracture associated with movement in rock; the proposed explanation remains a theory.

The map uses five different shadings and patterns for very high, high, moderate, low and very low damage risk. Darker areas occur in the northeast, parts of the Himalayan belt and Kachchh.

See Fig. 6.2 in your NCERT textbook

The high damage risk zone includes northern Punjab, eastern Haryana, Delhi, western Uttar Pradesh and northern Bihar, together with remaining parts of Jammu and Kashmir, Ladakh and Himachal Pradesh. Most areas considered safe belong to the stable Deccan plateau; this is not a claim that every peninsular location is risk-free.

What damage do earthquakes cause, and how can losses be reduced?

An earthquake becomes a calamity when it strikes densely populated areas. It can destroy settlements, industries, transport and communication networks. It also removes material possessions and social and cultural gains accumulated over generations, leaving people homeless and placing additional strain on developing economies.

How can one earthquake produce several effects?

Ground effects include fissures, or cracks in the ground, landslides, the rapid sliding of large masses of bedrock, and sinking. Bedrock is solid rock beneath soil and weathered material. Buildings and other structures may crack, slide, overturn, bend or collapse. Effects on water include waves and tsunamis, the sea waves generated by abrupt displacement of ocean water.

Surface waves can open fissures through which water and other materials escape and inundate nearby areas. Landslides often obstruct rivers and channels, forming reservoirs. Sometimes rivers change course, producing flooding and further damage. These linked effects can extend the disruption beyond the initial shaking.

Damaged transport and communication links also make timely relief difficult. The loss of a road or communication route affects both the people directly exposed and the ability of rescuers to reach them.

What measures support earthquake preparedness?

• Monitoring: Establish seismological centres, meaning earthquake-monitoring centres, and communicate information rapidly to vulnerable populations.
• Risk information: Prepare vulnerability maps and educate people about ways to minimise adverse effects.
• Construction controls: Modify house types and building designs, and discourage high-rise buildings, large industries and major urban centres in vulnerable areas.
• Safer structures: Require earthquake-resistant designs and light materials in major construction in vulnerable areas.

Note: It is not possible to prevent the occurrence of an earthquake. Monitoring, public education and safer construction seek to reduce losses; they do not remove the underlying tectonic forces.

How do tsunamis develop and affect coastal settlements?

Tsunamis, also called harbour waves or seismic sea waves, result when earthquakes or volcanic eruptions abruptly move the sea floor and displace ocean water. Normally, seismic waves cause one instantaneous vertical wave, followed by a series of afterwaves as the water seeks to restore its level.

Why are coastal effects severe?

In deep water, a tsunami has a very long wavelength, the distance between successive wave crests, and limited wave height. A crest is a wave's high point; a trough is its low point. A ship at sea is not much affected.

A tsunami raises a ship only a metre or two, with each rise and fall taking several minutes. In shallow water, its wavelength decreases while its period, the time between successive waves, remains unchanged, and wave height increases.

Sometimes the height can be up to 15 metres or more. On reaching the coast, the waves release enormous energy and water flows turbulently over land. Port towns, buildings and other settlements can suffer extensive destruction.

Coasts are densely populated and contain intense human activity. Consequently, loss of life and property is likely to be much higher from a tsunami than from other natural hazards in coastal areas. The physical force of the waves combines with the exposure of coastal populations.

Why is international cooperation needed?

The very large scale of losses makes tsunami mitigation difficult. Mitigating damage on this scale is beyond the capacity of an individual state or government. Combined international efforts are a possible way of dealing with the damage.

Following the tsunami of 26 December 2004, India volunteered to join the International Tsunami Warning System. Warning cooperation forms part of a broader response to a hazard whose effects extend across national boundaries.

Photograph: Tsunami Affected Area (NCERT Class 11 Figure 6.3). This photograph shows boats amid extensive scattered debris.

How do tropical cyclones form and damage coastal areas?

Tropical cyclones are intense low-pressure areas surrounded by high-velocity winds. Low pressure means atmospheric pressure lower than that of surrounding areas. These systems are confined to latitudes between 30 degrees north and 30 degrees south, positions measured north or south of the equator.

A cyclone acts like a heat engine. Moisture collected by winds over the sea undergoes condensation, changing from water vapour to liquid and releasing latent heat, heat associated with a change of state. This release supplies energy to the cyclone.

What initial conditions favour their development?

Scientists differ over the exact mechanism of a tropical cyclone. Initial conditions include a large, continuous supply of warm moist air, strong Coriolis force and atmospheric instability. The Coriolis force is the apparent deflecting influence of the earth's rotation on moving air. A further condition is the absence of strong winds that disturb the vertical transport of latent heat.

Strong Coriolis force prevents the central low pressure from filling. Its absence near the equator prohibits tropical cyclone formation between zero and five degrees latitude. Instability through the troposphere, the lowest atmospheric layer, creates local disturbances around which a cyclone develops.

How are Indian coasts affected?

Indian tropical cyclones originate over the Bay of Bengal and Arabian Sea. A monsoon is a large-scale seasonal reversal of winds. Most cyclones originate between 10 and 15 degrees north during the monsoon season, while Bay of Bengal cyclones mostly develop in October and November.

Severe coastal cyclonic storms often produce a storm surge, an abnormal rise in sea level. Strong surface winds and a steep pressure difference drive seawater across the coast, together with heavy rain. This inundates settlements and agricultural fields, damages crops and destroys structures.

The force of a cyclone decreases with increasing distance from the sea. Cyclone shelters, protective embankments, reservoirs and afforestation can help minimise damage. Afforestation means establishing forest cover; here it can reduce wind speed. Monitoring can make it possible to manage cyclonic hazards to some extent.

Why do floods occur, and what are their consequences in India?

Flooding occurs when rising water in channels spills over and inundates land and settlements. Floods are relatively slow in occurrence and often affect identifiable regions at expected times of year. Their causes are well established, although their effects can be severe.

How do natural processes and human actions interact?

Surface run-off, water flowing over the ground, can exceed the carrying capacity of rivers and streams. Water then spreads over neighbouring low-lying flood plains. Lakes and other inland water bodies can also receive more water than they can hold.

Prolonged intense rainfall, melting snow and ice, and coastal storm surges can produce floods. Reduced infiltration, the entry of water into the ground, and increased eroded material in rivers also contribute. Deforestation and unscientific agricultural practices can intensify these processes.

Obstruction of drainage channels and settlement on riverbeds and flood plains increase the intensity and seriousness of flooding. Human activity therefore contributes both to the development of floods and to the exposure of people and property.

The National Flood Commission identified 40 million hectares as flood-prone in India. Assam, West Bengal and Bihar are among the highly flood-prone states. Rivers in Punjab and Uttar Pradesh are vulnerable to occasional flooding.

Flash floods, rapidly developing floods, also affect Rajasthan, Gujarat, Haryana and Punjab. This is partly related to monsoon patterns and partly to blocked streams and river channels. Sometimes Tamil Nadu floods during November to January because of the retreating monsoon.

Shading identifies areas liable to flood. Extensive shaded stretches follow the Ganga and Brahmaputra river systems, while other shaded areas appear beside rivers and coastal stretches. The map also labels major rivers.

See Fig. 6.6 in your NCERT textbook

Case study: What does Majuli show about flood effects?

At Majuli in Assam, annual Brahmaputra floods deposit fertile silt and support good paddy crops. Silt is fine material carried and deposited by water. This is a positive effect, but such benefits are insignificant compared with the grave losses caused by floods.

Floods destroy crops, roads, railways, bridges and homes. People and cattle may be swept away, while contaminated water spreads disease. Protective embankments, dams, afforestation, removal of river-channel encroachments and reduced settlement on flood plains are measures for reducing damage.

What is drought, and how do its four types differ?

Drought is an extended period of shortage in available water. Inadequate precipitation, excessive evaporation and overuse of stored water, including groundwater, water stored beneath the ground, contribute to it. Precipitation is water falling from the atmosphere; evaporation is the change of liquid water into vapour.

Drought is complex because water availability interacts with soil moisture, water storage, surface run-off, crops, agricultural practices and social and ecological conditions. It cannot be understood simply as the absence of rain on a particular day.

Which part of the water system is affected?

An aquifer is a water-bearing underground rock or sediment layer. An ecosystem comprises organisms and their physical surroundings interacting as a system.

These types distinguish shortages in rainfall, crop-supporting moisture, water storage and the living environment. The distinction helps identify which aspect of a complex drought situation is being described.

Note: In the agricultural drought classification, an area with more than 30 per cent of its gross cropped area, land counted once for each crop grown on it during the year, under irrigation, the deliberate supply of water to crops, is excluded from the drought-prone category.

The condition is more than 30 per cent, not simply 30 per cent. It relates to agricultural drought classification and should not be treated as a statement that an irrigated area cannot experience any form of water shortage.

Where are drought-prone areas located in India?

Indian agriculture depends heavily on monsoon rainfall. A monsoon is a large-scale seasonal reversal of winds. Large variations and unpredictability in its behaviour explain why one region may face floods while another suffers drought, or why one region experiences both in different seasons.

How extensive is drought exposure?

Some estimates indicate that nearly 19 per cent of India's geographical area and 12 per cent of its population suffer due to drought each year. These estimates describe annual suffering and should be distinguished from the total area identified as drought-prone.

How does severity vary across regions?

Extreme drought-affected areas include most parts of Rajasthan, particularly Marusthali west of the Aravali hills, and the Kachchh region of Gujarat. Jaisalmer and Barmer receive less than 90 millimetres of average annual rainfall.

Severe drought-prone areas include parts of eastern Rajasthan, most of Madhya Pradesh, eastern Maharashtra, interior Andhra Pradesh, the Karnataka Plateau, northern interior Tamil Nadu, southern Jharkhand and interior Odisha.

Moderate drought-affected areas include northern Rajasthan, Haryana, southern Uttar Pradesh, remaining Gujarat, Maharashtra except Konkan, Jharkhand, the Coimbatore plateau of Tamil Nadu and interior Karnataka. Remaining parts of India can be considered either free or less prone to drought.

The legend distinguishes extreme, severe and moderate zones and a drought-free area. The darkest shading lies in western India; lighter shaded zones extend through parts of central and peninsular India.

See Fig. 6.7 in your NCERT textbook

How does drought affect people, and what responses are needed?

Drought has cascading effects, meaning that an initial shortage produces further connected consequences. Crop failure reduces food supplies, livestock lose fodder and people face shortages of drinking water. These effects damage both society and the physical environment.

What shortages develop?

Akal means scarcity of food grains, trinkal scarcity of fodder, and jalkal scarcity of water. Often all three shortages occur together; this condition, called trikal, is the most devastating. These terms distinguish connected shortages rather than separate causes of drought.

Large-scale deaths of cattle and other animals, and migration of people and livestock, are the most common sights in drought-affected areas. Water scarcity can force people to drink contaminated water, spreading waterborne diseases, meaning diseases transmitted through contaminated water.

How should immediate and long-term responses differ?

Immediate relief includes safe drinking water, medicines, fodder and water for cattle, together with moving people and livestock to safer places. These measures address present suffering and the urgent needs of affected communities.

Long-term measures include identifying groundwater potential and considering transfers of river water from surplus to deficit areas. Interlinking rivers and building reservoirs and dams should receive serious thought; these are proposals to consider, not an assurance that every project is suitable.

Satellite images can help identify groundwater potential and possible river basins for interlinking. Training people to grow drought-resistant crops can help with mitigation. Rainwater harvesting, collecting rainwater for use, can also be effective in minimising drought effects.

Planning must address both immediate and long-term consequences. Supplying drinking water during a crisis and strengthening water availability over time serve related but different purposes. A response that addresses only one of these leaves the other set of needs unresolved.

Why do landslides occur, and how can their impacts be reduced?

A landslide is the rapid sliding of a large mass of bedrock. Bedrock is solid rock beneath soil and weathered material. Landslides are largely controlled by highly localised factors, making information collection and monitoring difficult and very costly.

Relevant factors include rock conditions, slope, land use, vegetation and human activities. Landslides are generally less dramatic than earthquakes, tsunamis and cyclones, but their effects on the natural environment and national economy are in no way less severe.

Which areas have different levels of vulnerability?

Very high vulnerability includes unstable young mountains in the Himalayas and Andaman and Nicobar, steep high-rainfall areas in the Western Ghats and Nilgiris, northeastern regions, frequently shaken areas and places with intense road or dam construction.

High vulnerability includes all Himalayan states and northeastern states except the plains of Assam. The distinction from very high vulnerability rests on the combination, intensity and frequency of the controlling factors.

Moderate to low vulnerability includes low-rainfall areas such as Ladakh and Spiti, stable undulating areas of the Aravali, and lower-rainfall parts of the Ghats and Deccan plateau. These areas experience occasional landslides.

Mining and ground subsidence also cause landslides in states including Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala. A stable regional setting therefore does not remove every local cause of slope failure.

Why can local damage have distant consequences?

Landslides directly affect relatively small areas, yet blocked roads, damaged railway lines and obstructed river channels have far-reaching effects. Diverted rivers can cause floods. Travel and exchange between places become difficult, risky and costly, adversely affecting development.

Area-specific mitigation includes restricting construction of roads, dams and large settlements in highly vulnerable places. Agriculture should be limited to valleys and moderate slopes. Afforestation and bunds, embankments of earth or stone, can help reduce water flow.

Terrace farming, cultivation on step-like fields along slopes, should be encouraged in northeastern hill states where jhumming, slash-and-burn or shifting cultivation, remains prevalent. These measures must respond to local slope conditions and human activities.

How should disaster management operate before, during and after an event?

Disaster management combines preparation, emergency response and recovery. Hazards cannot all be eliminated, so mitigation and preparedness are essential. Different stages address different needs, but together they aim to reduce losses and strengthen the ability to face future disasters.

What are the three stages?

Evacuation means moving people from danger to safer places. Rehabilitation supports affected people in rebuilding their lives. Capacity-building strengthens the ability of people and institutions to deal with future events. These activities extend management beyond immediate rescue.

Why is cooperation important?

The Yokohama Strategy and Plan of Action for a Safer World emerged from the conference held in Yokohama, Japan, from 23 to 27 May 1994. It recognised that disaster losses had risen and that poor and disadvantaged groups were worst affected, particularly in developing countries.

The strategy affirmed each country's responsibility to protect its citizens. It gave priority to developing countries, particularly the least developed, landlocked and small-island developing states. It called for stronger national capacities and, where appropriate, legislation for prevention, mitigation and preparedness.

It also supported community participation, non-governmental organisations and cooperation between countries and regions. Priorities included institutional capacity, technology sharing, information exchange and mobilisation of resources. These measures connect local action with national and international support.

In India, establishment of the National Institute of Disaster Management represents a step towards improved disaster management. Its importance lies within the wider need to prepare vulnerable populations, organise effective relief and strengthen recovery rather than treating each disaster as an isolated emergency.

Glossary

• Natural hazard — An environmental element or circumstance with the potential to harm people, property or both.
• Natural disaster — A relatively sudden event causing widespread death, property loss and disruption beyond people's effective control.
• Vulnerability — Susceptibility of people, property or places to harm from a hazard.
• Mitigation — Measures intended to reduce the adverse impacts of a disaster.
• Preparedness — Planning and readiness that help people respond when a disaster occurs.
• Tectonic forces — Forces originating within the earth that produce widespread changes in landforms.
• Tsunami — Sea waves produced when abrupt sea-floor movement displaces ocean water.
• Storm surge — An abnormal rise in sea level associated with severe cyclonic storms.
• Flooding — Inundation of land and settlements when rising channel water spills over.
• Agricultural drought — Insufficient soil moisture to support crops, resulting in crop failure.
• Ecological drought — Water shortage that causes natural ecosystem productivity to fail and induces ecological damage.
• Bedrock — The solid rock that lies beneath soil and weathered surface material.
• Landslide — Rapid movement of a large mass of rock down a slope.
• Bund — An embankment of earth or stone used to conserve water and soil.
• Capacity-building — Strengthening the ability of people and institutions to cope with future disasters.

Common errors and misconceptions

• Misconception: Every natural hazard is already a disaster. Correct: A hazard is a potential source of harm; a disaster involves very large destruction and serious social disruption.
• Misconception: Human actions have no role in natural disasters. Correct: Deforestation, construction in fragile areas and settlement on flood plains can intensify damage and increase vulnerability.
• Misconception: Earthquakes occur only in the Himalayas. Correct: Gujarat and Maharashtra have also experienced severe earthquakes; the proposed explanation for some peninsular events remains a theory.
• Misconception: Monitoring prevents earthquakes. Correct: Earthquake occurrence cannot be prevented; preparedness, information and safer construction aim to reduce its adverse effects.
• Misconception: Fertile flood deposits outweigh flood losses. Correct: Floods can support crops through silt deposition, but these benefits are insignificant compared with the grave losses.
• Misconception: Drought means only low rainfall. Correct: Excessive evaporation and overuse of stored water also contribute, while different drought types concern rainfall, crops, water stores and ecosystems.
• Misconception: Land with exactly 30 per cent of gross cropped area irrigated meets the stated exclusion. Correct: The agricultural drought condition requires more than 30 per cent.
• Misconception: Disaster management ends with rescue. Correct: Rehabilitation, recovery and capacity-building continue after the emergency and prepare communities for future events.

Exam-style questions with model answers

Q1. An unstable slope has the potential to harm a settlement. A later event causes widespread deaths, property loss and serious social disruption. Using these facts, distinguish a hazard from a disaster. [2 marks]

1. The unstable slope is a natural hazard because it presents the potential for harm to people and property.
2. The later event is a disaster because that harm has become widespread destruction and serious disruption of social life.

Q2. The Indian plate moves north and northeast at one centimetre per year, the Eurasian plate obstructs it, energy accumulates while the plates are locked, and the lock eventually breaks, releasing energy along the Himalayan arch. Explain earthquake occurrence in four stages. [4 marks]

1. The Indian plate's northward and northeastward movement, at one centimetre per year, brings it against the obstruction of the Eurasian plate.
2. The obstruction prevents unrestricted movement, so the two plates become locked rather than moving freely past the boundary.
3. Energy accumulates while the plates remain locked, and excessive accumulation builds stress within this tectonic setting.
4. When the lock breaks, accumulated energy is suddenly released, producing earthquakes along the Himalayan arch.

Q3. A deep-water tsunami has a long wavelength and limited height. In shallow water its wavelength decreases, its period remains unchanged and its height increases, sometimes to 15 metres or more. At the coast it releases enormous energy over land. Explain the contrast between its effects offshore and at a densely settled coast. [3 marks]

1. Offshore, the long wavelength and limited wave height mean that a ship at sea is not much affected, despite the passage of the tsunami.
2. Near the coast, reduced wavelength with unchanged period accompanies increased wave height, sometimes reaching 15 metres or more.
3. The taller waves release enormous energy on reaching land; densely concentrated people and structures are exposed, so widespread coastal destruction can result.

Q4. Four areas show these conditions respectively: prolonged inadequate and uneven rainfall; insufficient soil moisture and crop failure; water availability in stores below what precipitation can replenish; and ecosystem productivity failure due to water shortage. Classify and explain each drought type. [4 marks]

1. The first area has meteorological drought because rainfall is inadequate over a prolonged period and is poorly distributed over time and space.
2. The second has agricultural drought, also called soil moisture drought, because crops lack the moisture needed for growth.
3. The third has hydrological drought because the shortage is expressed in the availability of water in storage.
4. The fourth has ecological drought because water shortage has caused ecosystem productivity to fail, leading to ecological distress and damage.

Q5. A flood-prone region has occupied river channels, densely settled flood plains, forest loss upstream, inadequate flood-protection embankments and damaged roads and homes. Using these conditions, explain five appropriate mitigation or relief measures. [5 marks]

1. Remove human encroachments from river channels. The supplied condition identifies occupied channels, so restoring their space addresses a human contribution to flood intensity.
2. Reduce settlement on flood plains. Depopulating these exposed areas reduces the number of people and homes directly threatened when rivers overflow.
3. Promote afforestation in the affected river system. This responds to the stated forest loss and forms part of measures for flood control.
4. Construct flood-protection embankments in flood-prone areas. This directly addresses the identified lack of protective works around vulnerable land and settlements.
5. Organise evacuation, shelters and emergency supplies for affected people. Damaged homes and roads create immediate relief needs alongside longer-term mitigation requirements.

Q6. A disaster-management plan proposes three groups of actions: vulnerability maps and awareness; evacuation, shelters and emergency supplies; rehabilitation, recovery and capacity-building. Identify the management stage represented by each group and explain its purpose. [3 marks]

1. Vulnerability mapping and awareness belong to pre-disaster management. They provide information about exposed areas and improve preparedness before the event occurs.
2. Evacuation, shelters and emergency supplies belong to management during a disaster. They support urgent rescue and relief for people facing danger and deprivation.
3. Rehabilitation, recovery and capacity-building belong to post-disaster management. They help victims recover and strengthen the ability to cope with future disasters.

Key takeaways

• A natural hazard presents potential harm; a disaster involves widespread destruction and serious disruption, and all hazards need not become disasters.
• Human activities can create disasters directly or intensify natural hazards through deforestation, fragile-area construction and occupation of flood plains.
• Earthquake losses require preparedness, public information and safer buildings because the occurrence of earthquakes cannot be prevented.
• Tsunamis can have limited wave height offshore and much greater height near shore, exposing densely populated coasts to severe destruction.
• Tropical cyclones draw energy from heat released during condensation, while strong winds and storm surges threaten coastal settlements.
• Floods bring some fertile deposits, but their destruction of crops, infrastructure, homes and lives greatly outweighs these benefits.
• The four drought types concern inadequate rainfall, insufficient soil moisture, depleted water stores and ecosystem damage; both immediate relief and long-term water planning matter.
• Landslide mitigation must suit local conditions, while disaster management as a whole includes preparation, emergency action and recovery.

Test yourself

What separates a hazard from a disaster?

A hazard has the potential to harm; a disaster involves very large damage, loss and disruption of social life.

Why can people increase vulnerability without causing the original natural event?

Settlement and construction in exposed places increase the people and property at risk, even when the natural event itself is not human-made.

What releases energy in the Himalayan earthquake mechanism?

Energy is suddenly released when the lock between the obstructed Indian plate and the Eurasian plate breaks.

What is a storm surge?

It is an abnormal rise in sea level associated with severe cyclonic storms, which can inundate coastal land.

What does the Majuli example demonstrate?

Annual Brahmaputra floods deposit fertile silt that supports good paddy crops, although such benefits are insignificant compared with flood losses.

How does agricultural drought differ from meteorological drought?

Agricultural drought concerns insufficient soil moisture for crops; meteorological drought concerns prolonged inadequate rainfall and its uneven distribution.

Why can a local landslide disrupt a wider area?

Blocked roads, damaged railway lines and obstructed rivers disrupt movement, can cause floods and make development more difficult.

What continues after emergency rescue and relief?

Rehabilitation, recovery and capacity-building help affected communities rebuild their lives and prepare to cope with future disasters.