Chapter 7 Natural Hazards And Disasters

Change is a fundamental aspect of nature, occurring continuously in various forms and scales. Some changes are gradual, like the evolution of landscapes or organisms. Others are sudden and rapid, such as volcanic eruptions, earthquakes, tsunamis, hailstorms, tornadoes, and dust storms. Changes can be localized or global in scale (like global warming). From nature's perspective, changes are value-neutral, but human perspective often labels them as good (seasonal changes, ripening fruit) or bad (earthquakes, floods, wars).

Natural disasters are a type of change that is widely perceived as bad and feared by humankind due to their destructive impact.

What Is A Disaster?

A disaster is formally defined as an unwelcome event resulting from forces largely beyond human control. It strikes suddenly, often with little warning, causing or threatening significant disruption to life and property, including death and injury to many people. Disasters necessitate a response that exceeds the capacity of normal emergency services.

Historically, disasters were viewed solely as consequences of natural forces, with humans as passive victims. However, it is now recognized that disasters can also be caused or intensified by human activities. Some human actions are directly responsible for disasters (e.g., industrial accidents like the Bhopal Gas Tragedy, nuclear disasters like Chernobyl, wars, pollution, release of greenhouse gases). Other activities indirectly contribute by altering the environment, accelerating or intensifying natural hazards (e.g., deforestation leading to landslides and floods, unscientific land use in vulnerable areas). Human-made disasters and the human impact on natural disasters have increased over time.

Preventing human-made disasters is possible with concerted efforts. Preventing natural disasters is much harder, so the focus is on mitigation (reducing impact) and management (preparing for and responding to events). Global initiatives like the World Conference on Disaster Management (Yokohama, Japan, 1994) and the establishment of institutions like India's National Institute of Disaster Management reflect a growing international effort towards disaster management.

While the terms are often used interchangeably, natural hazards and natural disasters are distinct but related phenomena. A natural hazard is a potential threat in the natural environment – an element or circumstance that has the potential to cause harm (e.g., steep slopes, ocean currents, extreme weather). A natural disaster is the realization of that hazard, a relatively sudden event causing large-scale death, property loss, and disruption to social systems. An event becomes a disaster when its destructive impact is very high.

Every disaster is unique due to local socio-environmental factors, social response, and how different groups cope. However, global data shows an increase in the magnitude, intensity, frequency, and damage caused by natural disasters, prompting increased global concern and efforts. The pattern of natural disasters is also changing, partly influenced by human intensification of activities in hazard-prone areas. For example, development on floodplains or coastal areas increases vulnerability to floods, cyclones, and tsunamis. Technological capacity has enabled human intervention in nature, sometimes inadvertently increasing exposure to hazards.

Table 7.1 lists some significant natural disasters globally in recent decades, illustrating the scale of loss (Note: The table provided lists events up to 2011).

*Deaths in 2004 and 2005 from news reports cited, 2011 from news reports cited.

The significant losses highlight the need for appropriate measures and international cooperation, leading to frameworks like the Yokohama Strategy and Plan of Action for a Safer World, adopted at the 1994 World Conference. This strategy emphasized national responsibility, priority for developing countries, capacity building, technology sharing, and international cooperation in disaster prevention, mitigation, and preparedness. It also designated 1990-2000 as the International Decade for Natural Disaster Reduction (IDNDR).

Classification Of Natural Disasters

Natural disasters can be broadly classified into four categories based on their origin (Table 7.2):

India, with its diverse geography and climate, is vulnerable to most of these natural disasters, leading to significant annual losses.

Earthquakes

Earthquakes are among the most unpredictable and destructive natural disasters. They are caused by the sudden release of energy within the Earth's crust, generating seismic waves that cause ground shaking. Tectonic earthquakes, resulting from the movement of tectonic plates, are the most devastating and affect large areas. Earthquakes related to volcanic eruptions, landslides, subsidence (mining areas), or reservoir impoundment have more localized impacts.

India is prone to earthquakes, especially in the Himalayan region, due to the ongoing northward movement and collision of the Indian plate with the Eurasian plate. This collision causes stress and energy accumulation, leading to sudden releases and earthquakes along the Himalayan arc. Highly vulnerable regions include Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, parts of West Bengal, and all northeastern states.

Paradoxically, severe earthquakes have also occurred in parts of the stable Peninsular block, like Gujarat and Maharashtra. This was initially difficult to explain but is now sometimes attributed to the reactivation of old fault lines or possible internal stresses within the plate.

Based on historical seismic data, India is divided into five earthquake zones based on damage risk (Very High, High, Moderate, Low, Very Low). The Very High Damage Risk Zone includes the northeastern states, areas along the Indo-Nepal border in Bihar, parts of Uttarakhand and Himachal Pradesh, Kashmir Valley, and the Kachchh region of Gujarat. The High Damage Risk Zone includes remaining parts of J&K, Ladakh, Himachal Pradesh, northern Punjab, eastern Haryana, Delhi, western UP, and northern Bihar. The Deccan plateau region is generally considered a Low to Very Low Damage Risk Zone.

Socio-environmental Consequences Of Earthquakes

Earthquakes cause widespread fear due to their suddenness and destructive power. They become calamities when striking densely populated areas. Their impact is not limited to immediate damage but affects various aspects:

Destruction of: Settlements, infrastructure (roads, rails, bridges), transport and communication networks, industries, and other developmental structures. They erase the material and socio-cultural achievements accumulated over generations.

Impact on Population: Rendering people homeless, causing injury and death. This puts immense pressure on the affected region's economy, particularly in developing countries.

Environmental Consequences: Surface seismic waves can create fissures, releasing water or gas. Earthquakes trigger landslides and rockfalls, which can block rivers, forming temporary lakes (impoundment). Changes in river courses caused by seismic activity or landslides can lead to subsequent flooding.

Effects Of Earthquakes

The destructive effects of earthquakes are multifaceted, impacting the ground, man-made structures, and water bodies (Table 7.3):

Earthquake Hazard Mitigation

Preventing earthquakes is not possible. Therefore, the focus is on reducing vulnerability and preparing for their impact:

• Establish earthquake monitoring centers (seismological centers) to monitor seismic activity and provide early warning in vulnerable areas. Using GPS can help track plate movements.
• Create vulnerability maps of the country to identify high-risk zones. Disseminate risk information and educate people on safety measures and minimizing impacts.
• Promote earthquake-resistant building designs using lightweight materials in vulnerable zones. Discourage or regulate the construction of high-rise buildings, large industries, and urban centers in the highest risk zones.
• Develop strict building codes and make it mandatory to adhere to earthquake-resistant standards for major construction projects in vulnerable areas.
• Improve transport and communication links in vulnerable areas to facilitate timely relief and rescue operations, as these are often destroyed during severe quakes.

Tsunami

Tsunamis (Japanese for "harbour waves"), also known as seismic sea waves, are giant waves caused by the sudden displacement of a large volume of ocean water. The most common causes are underwater earthquakes or volcanic eruptions that cause the seafloor to move abruptly. Landslides or meteorite impacts can also trigger tsunamis.

An initial disturbance creates a primary vertical wave. After this, a series of waves (afterwaves) are generated as the water surface oscillates to restore equilibrium. The speed of a tsunami wave depends on the water depth; it travels much faster in deep ocean than in shallow coastal waters.

In the open ocean, tsunamis have very long wavelengths (hundreds of kilometers) but relatively small wave heights (a meter or two). A ship in deep water might simply feel a gentle rise and fall over several minutes and may not even notice a tsunami passing. As a tsunami approaches shallow coastal areas, its speed decreases, but its wavelength shortens, and its height dramatically increases, sometimes reaching 15 meters or more. This is why tsunamis become highly destructive near the coast (they are effectively 'shallow water waves' because their wavelength is much greater than the water depth in coastal areas).

Tsunamis are most frequent along the Pacific Ring of Fire (coasts of Alaska, Japan, Philippines, Southeast Asia). However, they also occur in other oceans, as demonstrated by the devastating Indian Ocean tsunami of December 26, 2004, which resulted from a massive underwater earthquake off Sumatra (Indonesia) and caused widespread death and destruction across coastal areas of Indonesia, Sri Lanka, India (Figure 7.3 shows affected areas), Thailand, and other countries. Over 300,000 lives were lost in this event.

Map or image showing regions impacted by the destructive Indian Ocean Tsunami event of December 2004, highlighting the widespread coastal devastation.

Upon reaching the coast, tsunami waves release immense energy, causing turbulent water flow onto land, destroying buildings, infrastructure, and settlements. Coastal areas are particularly vulnerable due to high population density and intense human activity. Mitigating tsunami hazards is challenging due to their scale and suddenness. Given the scale of potential damage, international cooperation is essential for early warning and relief efforts. After the 2004 disaster, India joined the International Tsunami Warning System and established its own warning capabilities.

Tropical Cyclone

Tropical cyclones (also known as hurricanes, typhoons, or simply cyclones depending on the region) are intense low-pressure weather systems that form over warm tropical oceans. They are characterized by high-velocity winds spiraling inwards around a central low-pressure 'eye', heavy rainfall, and storm surges. They typically occur between $30^\circ$ N and $30^\circ$ S latitudes (Figure 7.4 shows wind and cyclone hazard zones).

Map illustrating regions around the world prone to high winds and the formation/impact of tropical cyclones.

Tropical cyclones function like heat engines, drawing energy from the release of latent heat when warm, moist air condenses as it rises over the ocean. While the exact mechanism is complex, specific initial conditions are necessary for their formation:

• A large area of warm ocean surface with temperatures generally above $27^\circ C$, providing abundant moisture and latent heat.
• Sufficient Coriolis force to initiate and maintain the cyclonic rotation (hence, they don't form very close to the equator where Coriolis force is negligible).
• Unstable atmospheric conditions throughout the troposphere that encourage rising air and localized disturbances.
• Absence of strong vertical wind shear (changes in wind speed/direction with height), which would disrupt the storm's vertical structure and inhibit heat transport.

Structure Of Tropical Cyclone

A mature tropical cyclone has a characteristic structure:

• Eye: The calm, clear area at the center, characterized by very low pressure and often subsiding air.
• Eyewall: A ring of towering cumulonimbus thunderstorms surrounding the eye. This zone experiences the strongest winds, most intense rainfall, and vigorous rising air.
• Spiral Rainbands: Bands of thunderstorms and precipitation that spiral inwards towards the eyewall from the outer parts of the storm.

Tropical cyclones have large pressure gradients, indicated by closely spaced isobars around the center. Pressure differences can be very high near the eyewall. Horizontally, they extend up to 500-1,000 km and vertically up to 12-14 km.

Spatio-temporal Distribution Of Tropical Cyclone In India

Due to its coastal location with the Bay of Bengal to the east and the Arabian Sea to the west, India is vulnerable to tropical cyclones originating in these basins. While many cyclones form between $10^\circ-15^\circ$ N latitude during the monsoon season (June-September), cyclones in the Bay of Bengal are particularly frequent and intense during the post-monsoon season (October-November). In this period, they typically originate between $16^\circ-20^\circ$ N latitude. By July, the origin shifts further north. The tracks and intensity of cyclones are influenced by various atmospheric conditions, including the position of the monsoon trough.

Consequences Of Tropical Cyclones

The destructive power of tropical cyclones is significant, especially in coastal areas:

• The energy from latent heat released over the warm ocean sustains the storm. As the cyclone moves inland, it loses its energy source and weakens.
• Coastal areas are hit by the strongest winds (averaging 180 km/h or more in severe storms) and heaviest rainfall.
• A major devastating consequence is the Storm Surge – an abnormal rise in sea level caused by the cyclone's low pressure and strong winds pushing seawater onto the coast.

Storm surges lead to the inundation of coastal human settlements and agricultural fields, damaging or destroying crops, buildings, and infrastructure. Densely populated delta regions (e.g., Godavari, Krishna, Kaveri deltas) are particularly vulnerable and experience recurring disasters from cyclones. Some cyclones also affect the coasts of West Bengal, Bangladesh, and Myanmar. Although less frequent, cyclones can also originate in the Arabian Sea and impact India's west coast.

Floods

Floods occur when water in channels (rivers, streams) rises and overflows, inundating adjacent land and human settlements. Unlike some other disasters, the causes of floods are generally well-understood, and they often occur in predictable regions and seasons.

Common causes of floods include:

• Surface runoff exceeding the carrying capacity of river channels.
• Overflow of lakes and other inland water bodies.
• High intensity or prolonged rainfall.
• Melting of ice and snow (especially contributing to river flow).
• Reduced infiltration rates into the soil (e.g., due to saturated soil or impervious surfaces).
• Presence of eroded material in water, reducing channel capacity.
• Storm surges (in coastal areas).

Floods are frequent globally, but particularly so and disastrous in South, Southeast, and East Asian countries. Human activities significantly influence floods. Indiscriminate deforestation increases runoff and erosion. Unscientific agricultural practices (e.g., cultivation on steep slopes) worsen soil erosion. Disturbances to natural drainage channels (e.g., encroachment, blockage) reduce their capacity. Colonization of flood-plains and river-beds places people and property directly in harm's way, increasing vulnerability and the intensity of impacts.

In India, recurrent floods cause substantial loss of life and property (Figure 7.6 shows flood hazard zones). The Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares as flood-prone. Assam, West Bengal, and Bihar are high flood-prone states. Rivers in states like Punjab and Uttar Pradesh are also vulnerable. Flash floods, rapid inundation often due to intense localized rainfall or sudden dam/embankment failure, have increased in states like Rajasthan, Gujarat, Haryana, and Punjab, partly due to rainfall patterns and partly due to blocked drainage channels. Tamil Nadu experiences floods during the retreating monsoon (November-January) due to cyclones.

Map illustrating regions across India that are identified as vulnerable to flooding based on historical data and geographical factors.

Image showing the Brahmaputra river during a flood event, illustrating the inundation of surrounding areas.

Consequence And Control Of Floods

Floods have serious consequences on the economy and society, particularly in frequently inundated areas:

• Destruction of crops, physical infrastructure (roads, railways, bridges), and human settlements.
• Rendering millions homeless.
• Loss of livestock.
• Spread of waterborne diseases (cholera, gastro-enteritis, hepatitis) in affected areas.

However, floods also have some limited positive contributions, like depositing fertile silt on agricultural fields (e.g., benefitting paddy cultivation in areas like Majuli, the world's largest riverine island in the Brahmaputra). But these benefits are outweighed by the losses.

Flood control and mitigation measures:

• Construction of flood protection embankments along rivers in flood-prone areas.
• Building dams and reservoirs in upper reaches to store excess water and regulate flow.
• Afforestation in catchments to improve soil infiltration and reduce runoff.
• Discouraging major construction and human encroachment activities in flood-plains and river channels, and relocating populations from highly vulnerable areas.
• Establishing flood forecasting and warning systems.
• In coastal areas prone to storm surges, establishing cyclone shelters.

Droughts

A drought is an extended period characterized by a severe shortage of water. This shortage is typically caused by inadequate precipitation, combined with factors like excessive evaporation and over-utilization of existing water resources (surface water in reservoirs/lakes and groundwater).

Image showing a landscape affected by drought, with dry, cracked soil and sparse or withered vegetation.

Drought is a complex phenomenon involving meteorological, hydrological, agricultural, socio-economic, and ecological aspects.

Types Of Droughts

Droughts are classified based on the aspect of water shortage:

• Meteorological Drought: Defined by a prolonged period with significant deficit of rainfall, and poor distribution over time and space compared to the average.
• Agricultural Drought (Soil Moisture Drought): Occurs when there is insufficient soil moisture to support crops, leading to crop failure. Areas with over 30% irrigated land are usually excluded from this category for classification purposes.
• Hydrological Drought: Results from reduced water levels in surface water storages (lakes, reservoirs) and groundwater sources (aquifers) below what precipitation can replenish, impacting water supply for various uses.
• Ecological Drought: When the lack of water leads to a failure in the productivity of a natural ecosystem, causing ecological stress and damage.

Recurrent droughts in various parts of India lead to severe socio-economic and ecological problems.

Drought Prone Areas In India

Indian agriculture is highly dependent on monsoon rainfall, making the country vulnerable to droughts. About 19% of India's geographical area and 12% of its population suffer from drought annually. Around 30% of the country's area is identified as drought-prone, affecting approximately 50 million people. Droughts are widespread, but some regions are more recurrently and severely affected than others (Figure 7.8 shows drought-prone zones).

Map illustrating regions across India that are identified as prone to different levels of drought severity.

• Extreme Drought Affected Areas: Most parts of Rajasthan (west of Aravali - Marusthali) and Kachchh region of Gujarat fall here. Includes districts like Jaisalmer and Barmer with very low annual rainfall (< 90 mm).
• Severe Drought Prone Area: Includes parts of eastern Rajasthan, most of Madhya Pradesh, eastern Maharashtra, interior parts of Andhra Pradesh and Karnataka Plateau, northern interior Tamil Nadu, and southern parts of Jharkhand and interior Odisha.
• Moderate Drought Affected Area: Covers northern Rajasthan, Haryana, southern UP, remaining parts of Gujarat, Maharashtra (except Konkan), Jharkhand, Coimbatore plateau (Tamil Nadu), and interior Karnataka.

The rest of India is considered less prone or free from drought. The frequent occurrence of droughts in some regions while others experience floods is mainly due to the large variations and unpredictability of the Indian monsoon.

Consequences Of Drought

Droughts have severe and wide-ranging effects:

• Agricultural Failure: Leading to scarcity of food grains ('akal'), fodder ('trinkal'), and water ('jalkal'). A shortage of all three is termed 'trikal'.
• Livestock and Human Impact: Large-scale death of cattle and other animals, forced migration of humans and livestock seeking food and water.
• Health Issues: Consumption of contaminated water due to scarcity leads to the spread of waterborne diseases (gastro-enteritis, cholera, hepatitis).
• Long-term Effects: Environmental degradation (soil erosion, desertification), economic losses, and social disruption.

Drought mitigation strategies need to address both immediate relief and long-term preparedness:

• Immediate: Providing safe drinking water, medical aid, food, fodder, and water for cattle. Arranging for temporary relocation of affected populations and livestock.
• Long-term:
  • Identifying groundwater potential (aquifers) and promoting sustainable groundwater use.
  • Transferring river water from surplus basins to deficit basins (e.g., inter-linking of rivers, construction of reservoirs and dams).
  • Promoting drought-resistant crop varieties and appropriate agricultural practices.
  • Implementing rainwater harvesting techniques (rooftop harvesting, check dams, tanks).
  • Using remote sensing and satellite data for monitoring drought conditions, identifying water resources, and planning interventions.
  • Educating and training communities in drought management strategies.

Landslides

Landslides are rapid downslope movements of a mass of rock, debris, or earth (Figure 7.9). While less dramatic than some other disasters, they can cause significant damage to the natural environment and economy, blocking roads, destroying infrastructure (railway lines), and causing river blockage (resulting in upstream flooding or damming).

Image showing a mass of soil, rock, or debris moving rapidly down a slope.

Unlike disasters controlled by large-scale factors, landslides are largely governed by highly localized conditions. Predicting their exact occurrence is difficult and costly. Landslide vulnerability varies across India based on factors like geology, geomorphology, slope angle, land-use, vegetation cover, and human activities.

Landslide Vulnerability Zones

India is divided into zones based on landslide risk:

• Very High Vulnerability Zone: Includes highly unstable, relatively young mountainous regions (Himalayas), high rainfall areas with steep slopes (Western Ghats, Nilgiris), northeastern regions, areas with frequent earthquakes, and areas with intense human activities (road/dam construction).
• High Vulnerability Zone: Areas with similar conditions to the very high zone, but with slightly different combinations, intensity, or frequency of controlling factors. Includes most Himalayan states and northeastern states (excluding Assam plains).
• Moderate to Low Vulnerability Zone: Areas with less precipitation (Trans-Himalayan regions), stable but undulating relief and low rainfall areas (Aravali), rain-shadow areas (Western/Eastern Ghats, Deccan plateau) experience occasional landslides, often linked to mining or subsidence in specific areas (Jharkhand, Odisha, Chhattisgarh, MP, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa, Kerala).
• Other Areas: Remaining parts of India (Rajasthan, Haryana, UP, Bihar, West Bengal - except Darjiling, Assam - except Karbi Anglong, southern coastal states) are generally considered safe from landslides.

Consequences Of Landslides

Although the direct impact area is localized, consequences can be far-reaching:

• Blocking roads and railway lines, disrupting transportation.
• Damming rivers due to rockfalls, leading to upstream flooding or potential downstream flash floods if the dam breaks.
• Loss of life and property.
• Making travel and access difficult and costly, hindering developmental activities in affected regions.

Mitigation

Strategies to reduce landslide risk are often area-specific:

• Restrict or regulate construction and development activities (roads, dams) in high vulnerability zones.
• Limit agricultural practices to valleys and gentler slopes; discourage shifting cultivation (Jhumming) in vulnerable hill states.
• Control development of large settlements in high-risk areas.
• Implement positive measures like large-scale afforestation on slopes to stabilize soil.
• Construct retaining walls, bunds, and drainage systems to manage water flow on slopes.
• Use engineering techniques to stabilize slopes where necessary.

Disaster Management

Disaster Management involves planning, preparing for, and responding to disasters to minimize their impact. Unlike earthquakes or tsunamis, cyclones are more predictable in terms of timing and path, allowing for some management through monitoring and forecasting. Measures like building cyclone shelters, embankments, dykes, and afforestation can reduce damage from cyclones, but vulnerability remains high in densely populated coastal areas in many countries. The Disaster Management Bill, 2005, in India defines disaster broadly, encompassing natural and human-made catastrophes that exceed a community's coping capacity.

Effective disaster mitigation and management involves a three-stage approach:

• Pre-disaster Management: Focuses on preparedness and prevention *before* a disaster strikes. This includes collecting data, preparing vulnerability maps, raising public awareness, developing disaster plans, and implementing preventive measures in vulnerable areas.
• During Disasters: Involves immediate emergency response operations, such as search and rescue, evacuation of affected populations, setting up temporary shelters and relief camps, and providing essential supplies (water, food, clothing, medical aid).
• Post-disaster Operations: Focuses on recovery and rehabilitation *after* the event. This includes providing long-term housing and support for victims and, importantly, capacity building to improve preparedness and resilience for future disasters.

These measures are crucial for countries like India, where a large proportion of the area and population are vulnerable to various disasters. The enactment of the Disaster Management Bill, 2005, and the establishment of the National Institute of Disaster Management are positive steps towards strengthening disaster preparedness and response in India.

Conclusion

In conclusion, disasters can be natural or human-induced. Not all natural hazards escalate into full-blown disasters, as vulnerability and preparedness play a key role. Since natural disasters cannot be entirely prevented, the most effective approach is focusing on disaster mitigation (reducing potential damage) and preparedness (planning for response). This involves a multi-stage process encompassing pre-disaster measures (planning, prevention, awareness), response during the event (rescue, relief), and post-disaster activities (rehabilitation, recovery, capacity building). These efforts are particularly important for countries like India, which faces significant vulnerability to a wide range of natural hazards.

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