Natural Hazards and Disasters Class 11 Geography

Natural hazards and disasters refer to events such as earthquakes, floods, cyclones, and droughts that result from natural processes. These events pose significant risks to human life, property, and the environment. The Chapter covers topics related to the causes, impacts, management, and mitigation strategies for natural disasters, emphasizing the importance of preparedness, early warning systems, and community resilience in reducing their adverse effects.

Natural Disasters

What is a Disaster?

Disaster is an undesirable occurrence resulting from forces that are largely outside human control, strikes quickly with little or no warning, which causes or threatens serious disruption of life and property including death and injury to a large number of people, and requires therefore, mobilisation of efforts in excess of that which are normally provided by statutory emergency services.

• Natural Hazards are elements of circumstances in the Natural environment that have the potential to cause harm to people or property or both.
• As compared to natural hazards, natural disasters are relatively sudden and cause large scale, widespread death, loss of property and disturbance to social systems and life over which people have a little or no control.

Question for Revision Notes - Natural Hazards and Disasters

Try yourself:The picture shows a disaster caused due to

• A.

  flood.
• B.

  landslide.
• C.

  soil erosion.
• D.

  subsidence.

Explanation

Landslide is the mass movement of rock, debris or earth down a slope. It includes a broad range of motions whereby falling, sliding and flowing under the influence of gravity dislodges the earth material.

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Yokohama Strategy and Plan of Action for a Safer World

All the member states of the United Nations and other states met at the World Conference on Natural Disaster Reduction in the city of Yokohama from May 23rd-27th 1994.
The resolution of the World Conference on Natural Disasters Reduction is as mentioned below:

• It will note that each country has the sovereign responsibility to protect its  citizens  from natural disasters;
• It will give priority attention to the developing countries, particularly the least developed, land-locked countries and small-island developing states;
• It will develop and strengthen national capacities and capabilities and, where appropriate, national legislation for natural and other disaster prevention, mitigation and preparedness, including the mobilisation of non-governmental organisations and participation of local communities;
• It will promote and strengthen sub-regional, regional and international cooperation in activities to prevent, reduce and mitigate natural and other disasters, with particular emphasis on:
  • human and institutional capacity-building and strengthening;
  • technology sharing: the collection, the dissemination and utilisation of information; and
  • mobilisation of resources.
  • It also declared the decade 1990-2000 as the International Decade for Natural Disaster

Natural Disasters And Hazards In India

Earthquakes

• Earthquakes are highly unpredictable and immensely destructive natural disasters.
• Tectonic earthquakes, caused by sudden energy release during earth's crust movements, are particularly devastating and have extensive reach.
• Compared to tectonic earthquakes, those associated with volcanic eruptions, rockfalls, landslides, and other factors have limited impact.
• The Indian plate moves about one centimeter annually north and northeastward, encountering resistance from the Eurasian plate, resulting in energy accumulation and eventual release, leading to earthquakes along the Himalayan arch.
• Vulnerable states include Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, Darjeeling, and the northeastern states.
• Some scientists propose the emergence of a fault line along the Bhima (Krishna) river in Maharashtra, suggesting potential plate breakdown.
• National Geophysical Laboratory, Geological Survey of India, Department of Meteorology, Government of India, along with the recently formed National Institute of Disaster Management, following five earthquake zones:

• Very high damage risk zone
• High damage risk zone
• Moderate damage risk zone
• Low damage risk zone
• Very low damage risk zone.

• North-east states, areas to the north of Darbhanga and Araria along the Indo-Nepal border in Bihar, Uttarakhand, Western Himachal Pradesh (around Dharamshala) are in Very high damage risk zone.
• The remaining parts of Jammu and Kashmir, Himachal Pradesh, Northern parts of Punjab, Eastern parts of Haryana, Delhi, Western Uttar Pradesh, and Northern Bihar fall under the High Damage Risk Zone.
• Remaining parts of the country fall under moderate to very Low Damage Risk Zone. Most of the areas that can be considered safe are from the stable landmass covered under the Deccan plateau.

Earthquake

Socio-Environmental Consequences of Earthquakes

• It becomes a calamity when it strikes the areas of high density of population.
• It not only damages and destroys the settlements, infrastructure, transport and communication network, industries and other developmental activities but also robs the population of their material and socio-cultural gains that they have preserved over generations.
• It renders them homeless, which puts an extra-pressure and stress, particularly on the weak economy of the developing countries.

Effects of Earthquakes

Earthquake Hazard Mitigation 

Unlike other disasters, the damages caused by earthquakes are more devastating. Since it also destroys most of the transport and communication links, providing timely relief to the victims becomes difficult. It is not possible to prevent the occurrence of an earthquake; hence, the next best option is to emphasis on disaster preparedness and mitigation rather than curative measures such as:

• Establishing earthquake monitoring centres (seismological centres) for regular monitoring and fast dissemination of information among the people in the vulnerable areas. Use of GeographicalPositioning System (GPS) can be of great help in monitoring the movement of tectonic plates. 
• Preparing a vulnerability map of the country and dissemination of vulnerability risk information among the people and educating them about the ways and means minimising the adverse impacts of disasters.
• Modifying the house types and building- designs in the vulnerable areas and discouraging construction of high-rise buildings, large industrial establishments and big urban centres in such areas.
• Finally, making it mandatory to adopt earthquake-resistant designs and use light materials in major construction activities in the vulnerable area

Tsunami

• Earthquakes and volcanic eruptions that cause the sea-floor to move abruptly resulting in sudden displacement of ocean water in the form of high vertical waves are called tsunamis (harbour waves) or seismic sea waves. Normally, the seismic waves cause only one instantaneous vertical wave; but, after the initial disturbance, a series of afterwaves are created in the water that oscillate between high crest and low trough in order to restore the water level.
• The speed of wave in the ocean depends upon the depth of water. It is more in the shallow water than in the ocean deep.
• As a result of this, the impact of tsunami is less over the ocean and more near the coast where they cause large-scale devastations. Therefore, a ship at sea is not much affected by tsunami and it is difficult to detect a tsunami in the deeper parts of sea
• Thus, these are also called Shallow Water Waves. Tsunamis are frequently observed along the Pacific ring of fire, particularly along the coast of Alaska, Japan, Philippines, and other islands of South- east Asia, Indonesia, Malaysia, Myanmar, Sri Lanka, and India etc.
• The mitigation of hazards created by tsunami is difficult, mainly because of the fact that losses are on a much larger scale-combined efforts at the international levels are the possible ways of dealing with these disasters as has been in the case of the tsunami that occurred on 26th December 2004 in which more than 300,000 people lost their lives. India has volunteered to join the International Tsunami Warning System after the December 2004 tsunami disaster.

Tropical Cyclone

• Tropical cyclones are intense low-pressure areas confined to the area lying between 30° N and 30° S latitudes, in the atmosphere around which high velocity winds blow.
• Horizontally, it extends up to 500-1,000 km and vertically from surface to 12-14 km. 
• A tropical cyclone or hurricane is like a heat engine that is energised by the release of latent heat on account of the condensation of moisture that the wind gathers after moving over the oceans and seas.

Initial conditions for the emergence of a tropical cyclone

• Large and continuous supply of warm and moist air that can release enormous latent heat.
• Strong Coriolis force that can prevent filling of low pressure at the centre (absence of Coriolis force near the equator prohibits the formation of tropical cyclone between 0°-5°latitude).
• Unstable condition through the troposphere that creates local disturbances around which a cyclone develops.
• Finally, absence of strong vertical wind wedge, which disturbs the vertical transport of latent heat.

Structure of Tropical Cyclone

• Tropical cyclones are characterised by large pressure gradients. The centre of the cyclone is mostly a warm and low-pressure, cloudless core known as eye of the storm.
• Generally, the isobars are closely placed to each other showing high-pressure gradients. Normally, it varies between 14- 17mb/100 km, but sometimes it can be as high as 60mb/100km. Expansion of the wind belt is about 10-150 km from the centre.

Spatio-temporal Distribution of Tropical Cyclone in India

• Owing to its Peninsular shape surrounded by the Bay of Bengal in the east and the Arabian Sea in the west, the tropical cyclones in India also originate in these two important locations.
• Though most of the cyclones originate between 10°-15° north latitudes during the monsoon season, yet in case of the Bay of Bengal, cyclones mostly develop during the months of October and November.
• Here, they originate between 16°-2° N latitudes and to the west of 92° E. By July the place of origin of these storms shifts to around 18° N latitude and west of 90°E near the Sunderban Delta.
• A surge is generated due to interaction of air, sea and land. The cyclone provides the driving force in the form of very high horizontal pressure-gradient and very strong surface winds. The sea water flows across the coast along with strong winds and heavy downpour.

Floods

• The causes of floods are well- established. relatively slow in occurrences and often, occur in well-identified regions and within expected time in a year. Floods occur commonly when water in the form of surface run-off exceeds the carrying capacity of the river channels and streams and flows into the neighbouring low-lying flood plains.
• Floods can also be caused due to a storm surge (in the coastal areas), high intensity rainfall for a considerably longer time period, melting of ice and snow, reduction in the infiltration rate and presence of eroded material in the water due to higher rate of soil erosion. Though floods occur frequently over wide geographical area having disasterous ramifications in many parts of the world, floods in the South, Southeast and East Asian countries, particularly in China, India and Bangladesh, are frequent and equally disastrous.
• Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares of land as flood-prone in India, Assam, West Bengal and Bihar are among the high flood-prone states of India. Apart from these, most of the rivers in the northern states like Punjab and Uttar Pradesh, are also vulnerable to occasional floods.

Consequence and Control of Flood

• Affected Regions: Assam, West Bengal, Bihar, Uttar Pradesh, Orissa, Andhra Pradesh, Tamil Nadu, Gujarat, Punjab, Rajasthan, Northern Gujarat, and Haryana.
• Economic and Social Impact: Floods damage crops, infrastructure like roads and bridges, and displace millions, washing away homes and livestock.
• Health Issues: Spread of water-borne diseases such as cholera, gastroenteritis, and hepatitis.

Positive Contributions: Floods also benefits the agriculture as they deposit fertile silt on fields, improving soil fertility and aiding crop production, notably in Majuli (Assam) with its paddy crops.

Control Measures by Government:

• Infrastructure: Construction of embankments, dams, and promoting afforestation.
• Policy Changes: Discouraging construction in flood-prone areas, especially in the upper reaches of rivers.
• Land Management: Removing human encroachment from river channels and reducing population density in flood plains, particularly in regions prone to flash floods.
• Emergency Preparedness: Establishment of cyclone centers in coastal areas to manage storm surges.

Droughts

• The term ‘drought’ is applied to an extended period when there is a shortage of water availability due to inadequate precipitation, excessive rate of evaporation and over­utilisation of water from the reservoirs and other storages, including the ground water.
• Drought is a complex phenomenon as it involves elements of meteorology like precipitation, evaporation, evapo- transpiration, ground water, soil moisture, storage and surface run-off, agricultural practices, particularly the types of crops grown, socio-economic practices and ecological conditions.

Types of Droughts

• Meteorological Drought: It is a situation when there is a prolonged period of inadequate rainfall marked with mal-distribution of the same over time and space.
• Agricultural Drought: It is also known as soil moisture drought, characterised by low soil moisture that is necessary to support the crops, thereby resulting in crop failures. Moreover, if an area has more than 30 per cent of its gross cropped area under irrigation, the area is excluded from the drought-prone category.
• Hydrological Drought: It results when the availability of water in different storages and reservoirs like aquifers, lakes, reservoirs, etc. falls below what the precipitation can replenish Ecological Drought : When the productivity of a natural ecosystem fails due to shortage of water and as a consequence of ecological distress, damages are induced in the ecosystem.
• Ecological drought: It occurs when a natural ecosystem's productivity declines due to a water shortage, leading to ecological distress and subsequent damage to the ecosystem.

Drought Prone Areas in India

• Extreme Drought Affected Areas: Most parts of Rajasthan, particularly areas to the west of the Aravali hills, i.e. Marusthali and Kachchh regions of Gujarat fall in this category. Included here are also the districts like Jaisalmer and Barmer from the Indian desert that receive less that 90 mm average annual rainfall.
• Severe Drought Prone Area: Parts of eastern Rajasthan, most parts of Madhya Pradesh, eastern parts of Maharashtra, interior parts of Andhra Pradesh and Karnataka Plateau, northern parts of interior Tamil Nadu and southern parts of Jharkhand and interior Orissa are included in this category.
• Moderate Drought Affected Area: Northern parts of Rajasthan, Haryana, southern districts of Uttar Pradesh, the remaining parts of Gujarat, Maharashtra except Konkan, Jharkhand and Coimbatore plateau of Tamil Nadu and interior Karnataka are included in this category. Crop failure leading to scarcity of food grains (akal), fodder (trinkal), inadequate rainfall, resulting in shortage of water (jalkal), and often shortage in all the three (trikal) is most devastating Landslides.

Consequences of Drought

Immediate consequences:

• Food and Water Shortages: Insufficient rainfall leads to crop failure, scarcity of food grains, and inadequate water supply.
• Health Risks: Drought increases the use of contaminated water, spreading diseases like gastro-enteritis, cholera, and hepatitis.
• Livestock and Human Migration: Lack of fodder and water drives migration of humans and livestock from drought-stricken areas.

Immediate Measures:

• Relief Efforts: Distribution of safe drinking water, essential medicines, and resources for livestock.
• Resettlement: Relocating people and livestock to safer locations.

Long-term Strategies:

• Water Management: Identifying ground water sources like aquifers, transferring river water from surplus to deficit regions, and planning for inter-linking of rivers.
• Agricultural Adaptation: Promoting drought-resistant crops and rainwater harvesting to mitigate drought effects.
• Technology and Training: Utilizing remote sensing for planning and training in drought-resistant farming practices.

Landslide Vulnerability Zones

• Very High Vulnerability Zone: Highly unstable, relatively young mountainous areas in the Himalayas and Andaman and Nicobar, high rainfall regions with steep slopes in the Western Ghats and Nilgiris, the north-eastern regions, along with areas that experience frequent ground-shaking due to earthquakes, etc. and areas of intense human activities, particularly those related to construction of roads, dams, etc. are included in this zone.
• High Vulnerability Zone: Areas that have almost similar conditions to those included in the very high vulnerability zone are also included in this category. The only difference between these two is the combination, intensity and frequency of the controlling factors. All the Himalayan states and the states from the north-eastern regions except the plains of Assam are included in the high vulnerability zones.
• Moderate to Low Vulnerability Zone: Areas that receive less precipitation such as Trans- Himalayan areas of Ladakh and Spiti (Himachal Pradesh), undulated yet stable relief and low precipitation areas in the Aravali, rain shadow areas in the Western and Eastern Ghats and Deccan plateau also experience occasional landslides. Landslides due to mining and subsidence are most common in states like Jharkhand, Orissa, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala.

Landslide

Consequences of Landslides

Landslides have relatively small and localised area of direct influence, but roadblock, destruction of railway lines and channel- blocking due to rock-falls have far-reaching consequences. Diversion of river courses due to landslides can also lead to flood and loss of life and property. It also makes spatial interaction difficult, risky as well as a costly affair, which, in turn, adversely affects the developmental activities in these areas.

Mitigation 

• It is always advisable to adopt area-specific measures to deal with landslides.
• Restriction on the construction and other developmental activities such as roads and dams, limiting agriculture to valleys and areas with moderate slopes, and control on the development of large settlements in the high vulnerability zones, should be enforced. This should be supplemented by some positive actions like promoting large-scale afforestation programmes and construction of bunds to reduce the flow ofwater.
• Terrace farming should be encouraged in the northeastern hill states where Jhumming (Slash and Burn/Shifting Cultivation) is still prevalent.

Disaster Management

The Disaster Management Bill, 2005, defines disaster as a catastrophe, mishap, calamity or grave occurrence affecting any area, arising from natural or man-made causes, or by accident or negligence which results in substantial loss of life or human suffering or damage to, and destruction of, environment, and is of such nature or magnitude as to be beyond the coping capacity of the community of the affected area.

There are three stages involved in disaster mitigation and management:

• Pre-disaster management involves generating data and information about the disasters, preparing vulnerability zoning maps and spreading awareness among the people about these. Apart from these, disaster planning, preparedness and preventive measures are other steps that need to be taken in the vulnerable areas.
• During disasters, rescue and relief operations such as evacuation, construction of shelters and relief camps, supplying of water, food, clothing and medical aids etc. should be done on an emergency basis.
• Post-disaster operations should involve rehabilitation and recovery of victims.