Natural Disasters and Hazards in India

India’s vulnerability to natural disasters is not an accident of geography alone. The country’s vast and diverse physical landscape, combined with a long colonial past, persistent social inequalities, and a very large population, has made it especially prone to disaster. Scholars have long described India as a “subcontinent” and a “land of unity in diversity” precisely because of this geographical and cultural vastness — but that same vastness multiplies the risk. When a disaster strikes, it is rarely just a physical event; it becomes a human tragedy because of where people live, how they are organised, and how much they have to lose.

Earthquakes

Among all natural disasters, earthquakes are the most unpredictable and the most destructive. The quakes that cause the greatest devastation are tectonic in origin — they come from a sudden release of energy during movements in the earth’s crust, producing a series of earth movements. Their area of influence is enormous. By contrast, earthquakes linked to volcanic eruptions, rock falls, landslides, subsidence (especially in mining areas), or the impounding of dams and reservoirs affect only limited areas and cause far less damage.

The Indian plate is moving north and northeast at about one centimetre per year, but the Eurasian plate blocks this movement from the north. The two plates are effectively locked together, and energy accumulates at different points over time. When the stress becomes too great, the lock breaks and the sudden release of energy triggers earthquakes along the Himalayan arch. The most vulnerable areas are Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, the Darjeeling subdivision of West Bengal, and all seven states of the northeast. Severe quakes have also struck central-western India — Gujarat in 1819, 1956 and 2001, and Maharashtra in 1967 and 1993.

For a long time, scientists struggled to explain why earthquakes occurred in the Peninsular block, one of the oldest, most stable and mature landmasses on earth. Recently, some earth scientists have proposed that a fault line has emerged along the river Bhima (Krishna) near Latur and Osmanabad in Maharashtra, with energy building up along it, and that the Indian plate itself may be breaking down.

The National Geophysical Laboratory, the Geological Survey of India, the Department of Meteorology, and the National Institute of Disaster Management analysed more than 1,200 earthquakes that have struck India over the years. On this basis, they divided the country into five earthquake zones:

1. Very high damage risk zone
2. High damage risk zone
3. Moderate damage risk zone
4. Low damage risk zone
5. Very low damage risk zone

The first two zones have experienced the most devastating earthquakes. The very high damage risk zone includes the northeastern states, areas north of Darbhanga and Araria along the Indo-Nepal border in Bihar, Uttarakhand, western Himachal Pradesh around Dharamshala, the Kashmir Valley, and Kuchchh in Gujarat. The high damage risk zone covers the rest of Jammu and Kashmir, Ladakh, Himachal Pradesh, northern Punjab, eastern Haryana, Delhi, western Uttar Pradesh, and northern Bihar. The rest of the country falls into the moderate to very low damage risk zones. The safest areas are on the stable landmass of the Deccan plateau.

Socio-Environmental Consequences of Earthquakes

Earthquakes inspire fear because of their scale, magnitude and suddenness — they spread destruction without discrimination. They become a calamity when they strike densely populated areas. Beyond destroying settlements, infrastructure, transport and communication networks, industries and developmental activities, they rob people of material and socio-cultural gains preserved over generations. Survivors are left homeless, which places extra pressure on the already weak economies of developing countries.

Effects of Earthquakes

The effects of an earthquake are all-encompassing. On the ground, they cause fissures, slidings and landslides. On manmade structures, they cause cracking, overturning, buckling and collapse. On water bodies, they produce waves, hydrodynamic pressure, earth pressure and tsunamis. Possible chain-effects include liquefaction and settlement.

Earthquakes also have serious environmental consequences. Surface seismic waves create fissures in the upper layers of the crust through which water and other volatile materials gush out, inundating neighbouring areas. Earthquakes trigger landslides that can block rivers and channels, forming reservoirs. Sometimes rivers change their course entirely, causing floods and other calamities.

Earthquake Hazard Mitigation

Earthquake damage is more devastating than that of other disasters because it also destroys the transport and communication links needed to deliver timely relief. Since earthquakes cannot be prevented, the focus must be on preparedness and mitigation rather than cure. The key measures are:

• Establishing earthquake monitoring (seismological) centres for regular monitoring and rapid dissemination of information. GPS can help track the movement of tectonic plates.
• Preparing a vulnerability map of the country and sharing risk information with people, while educating them on minimising adverse impacts.
• Modifying house types and building designs in vulnerable areas, and discouraging high-rise buildings, large industrial establishments and big urban centres there.
• Making it mandatory to adopt earthquake-resistant designs and use light materials in major construction in vulnerable areas.

Tsunami

Tsunamis, also called harbour waves or seismic sea waves, are caused by earthquakes and volcanic eruptions that abruptly move the sea floor, displacing ocean water as high vertical waves. Normally, seismic waves produce only one instantaneous vertical wave, but after the initial disturbance a series of afterwaves oscillate between high crest and low trough as the water tries to restore its level.

The speed of a wave depends on water depth — it is greater in shallow water than in the deep ocean. So the impact of a tsunami is less over the open ocean and far greater near the coast. A ship at sea is barely affected, and a tsunami is hard to detect in deep water because there it has a very long wavelength and limited wave height. It raises a ship only a metre or two, with each rise and fall taking several minutes. But when a tsunami enters shallow water, its wavelength shrinks while its period stays the same, so the wave height increases — sometimes to 15 metres or more. This is why tsunamis are also called shallow water waves.

Tsunamis are frequent along the Pacific ring of fire, especially the coasts of Alaska, Japan, the Philippines and other Southeast Asian islands, as well as Indonesia, Malaysia, Myanmar, Sri Lanka and India. When they reach the coast, they release enormous stored energy and water flows turbulently onto land, destroying port cities, towns, structures and settlements. Because coastal areas are densely populated and centres of intense human activity worldwide, tsunami losses are far higher than those from other coastal hazards.

Mitigation is difficult because the losses are on such a large scale that no single state or government can cope alone. International cooperation is essential. The tsunami of 26 December 2004, in which more than 300,000 people died, is the clearest example. After that disaster, India volunteered to join the International Tsunami Warning System.

Tropical Cyclone

Tropical cyclones are intense low-pressure areas between 30° N and 30° S latitudes, around which high-velocity winds blow. Horizontally they extend 500 to 1,000 km, and vertically from the surface to 12–14 km. A tropical cyclone or hurricane works like a heat engine, energised by the release of latent heat when moisture the wind gathered over oceans and seas condenses.

Scientists differ on the exact mechanism, but four initial conditions are needed:

• A large and continuous supply of warm, moist air that can release enormous latent heat.
• A strong Coriolis force to prevent the low pressure at the centre from filling in. The absence of this force near the equator is why tropical cyclones do not form between 0° and 5° latitude.
• Unstable conditions through the troposphere, creating local disturbances around which a cyclone develops.
• The absence of a strong vertical wind wedge, which would disturb the vertical transport of latent heat.

Spatio-Temporal Distribution in India

Because of its peninsular shape, surrounded by the Bay of Bengal to the east and the Arabian Sea to the west, India’s tropical cyclones originate in these two locations. Most cyclones form between 10° and 15° N during the monsoon season. In the Bay of Bengal, cyclones mostly develop in October and November, originating between 16° and 20° N and west of 92° E. By July, the place of origin shifts to around 18° N and west of 90° E, near the Sunderban Delta.

Consequences of Tropical Cyclones

Since a cyclone draws its energy from latent heat released by warm moist air, its force weakens with distance from the sea. In India, cyclonic force decreases as one moves away from the Bay of Bengal and the Arabian Sea. Coastal areas are therefore struck by severe cyclonic storms with an average velocity of 180 km/h. These storms often cause an abnormal rise in sea level called a storm surge.

A surge is generated by the interaction of air, sea and land. The cyclone supplies the driving force through a very high horizontal pressure gradient and very strong surface winds. Sea water flows across the coast along with the winds and heavy rain, inundating human settlements and agricultural fields, damaging crops and destroying human-made structures.

Floods

Flooding is the inundation of land and human settlements when water rises in channels and spills over. Unlike other natural disasters, the causes of floods are well established. Floods are relatively slow in occurrence and often strike well-identified regions within an expected time each year.

Floods occur when surface run-off exceeds the carrying capacity of river channels and streams, spilling into neighbouring low-lying flood plains. Sometimes the water even exceeds the capacity of the lakes and inland water bodies into which the rivers flow. Floods can also be caused by storm surges in coastal areas, high-intensity rainfall over a long period, melting of ice and snow, reduced infiltration rates, and eroded material in the water from high rates of soil erosion.

Floods are frequent and disastrous across South, Southeast and East Asia, especially in China, India and Bangladesh. Unlike other natural disasters, human beings play a major role in both the genesis and spread of floods. Indiscriminate deforestation, unscientific agricultural practices, disturbances to natural drainage channels, and the colonisation of flood plains and river beds all increase the intensity, magnitude and gravity of floods. …