Change is a continuous, universal law of nature, varying in magnitude, intensity, and scale. While natural changes are value-neutral, human perspectives classify them as desirable or undesirable. Undesirable, rapid changes outside human control are classified as hazards or disasters.
Though often used interchangeably, Natural Hazards and Natural Disasters are distinct concepts:
Natural disasters are broadly classified into four major categories as shown below:
| Atmospheric | Terrestrial | Aquatic | Biological |
|---|---|---|---|
| Blizzards, Thunderstorms, Lightening, Tornadoes, Tropical Cyclones, Droughts, Hailstorms, Frost, Heat/Cold Waves (Loo) | Earthquakes, Volcanic Eruptions, Landslides, Avalanches, Subsidence, Soil Erosion | Floods, Tidal Waves, Storm Surges, Tsunamis | Plants and Animals as colonisers (e.g., Locusts), Insect infestations, Fungal, Bacterial, and Viral diseases (e.g., Bird Flu, Dengue) |
Earthquakes are highly destructive and unpredictable tectonic disasters resulting from a sudden release of energy in the Earth's crust. In India, tectonic earthquakes are highly devastating due to the constant northward movement of the Indian plate at a rate of $1\text{ cm/year}$, colliding with the Eurasian plate.
The National Institute of Disaster Management and other bodies classify India into five earthquake zones:
The multi-dimensional impacts of earthquakes are categorized below:
| On Ground | On Manmade Structures | On Water |
|---|---|---|
| Fissures, Settlements, Landslides, Liquefaction, Earth Pressure, Chain-effects | Cracking, Slidings, Overturning, Buckling, Collapse, Chain-effects | Waves, Hydro-Dynamic Pressure, Tsunamis, Chain-effects |
A Tsunami (harbour wave) is a series of extremely long-wavelength ocean waves generated by the rapid displacement of water, usually caused by submarine earthquakes or volcanic eruptions.
In deep water, tsunamis have long wavelengths and low wave heights, making them difficult to detect. As they enter shallow coastal waters, their speed decreases, causing the wave energy to compress and the wave height to rise dramatically (up to $15\text{ m}$ or more), resulting in catastrophic coastal destruction.
Due to the scale of damage, individual state mitigation is difficult. India has joined the International Tsunami Warning System following the devastating Indian Ocean Tsunami of December 26, 2004.
Tropical Cyclones are intense low-pressure areas confined to latitudes between $30^\circ\text{ N}$ and $30^\circ\text{ S}$. They act as thermal engines powered by the release of latent heat of condensation.
In India, cyclones originate in both the Bay of Bengal and the Arabian Sea. Bay of Bengal cyclones are more frequent and intense, particularly during October and November. The primary hazard is the Storm Surge—an abnormal rise in sea level that inundates low-lying coastal settlements and agricultural fields.
Floods occur when water in a channel exceeds its carrying capacity, overflowing into adjacent floodplains. Unlike other disasters, floods are relatively slow to rise and occur in well-identified regions.
Floods are caused by heavy rainfall, storm surges, melting snow, or human activities like deforestation and unscientific land use. The Rashtriya Barh Ayog has identified $40\text{ million hectares}$ of land as flood-prone in India, with Assam, Bihar, and West Bengal being the worst affected.
Floods destroy crops, damage infrastructure, and spread waterborne diseases like cholera and hepatitis. However, they also deposit fertile silt. Control measures include constructing embankments, dams, afforestation, and removing human encroachments from river channels.
A Drought is an extended period of water shortage caused by inadequate precipitation, high evaporation, and over-utilization of water resources.
Mitigation involves distributing safe drinking water and fodder, inter-linking rivers, constructing reservoirs, rainwater harvesting, and promoting drought-resistant crops.
A Landslide is the rapid downward movement of a large mass of rock, debris, or earth under the influence of gravity. They are highly localized and influenced by geology, slope, and human activities.
Mitigation includes restricting construction on fragile slopes, promoting terrace farming, and implementing large-scale afforestation programmes.
Disaster management involves structured planning across three distinct stages:
The Government of India formalized these steps through the Disaster Management Bill, 2005 and the establishment of the National Institute of Disaster Management.