🃏 Natural hazards (Geography)

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What is a disaster? — An undesirable event, largely beyond human control, that strikes quickly with little or no warning, seriously disrupts life and property, and needs more help than the normal emergency services can give.

Hazard or disaster? — A natural hazard is something in the environment that could cause harm — ocean currents, steep unstable Himalayan slopes, extreme desert or glacial climates. It becomes a disaster when it causes large-scale, sudden death, loss of property and disruption.

Human-made disasters — Some disasters are caused directly by people — the Bhopal gas tragedy, the Chernobyl nuclear disaster, wars, CFCs and greenhouse gases, pollution. Others are made worse indirectly: landslides and floods from deforestation, unscientific land use and building in fragile areas.

Four kinds — Atmospheric (blizzards, thunderstorms, lightning, tornadoes, tropical cyclones, drought, hailstorms, frost, heat waves or loo, cold waves); terrestrial (earthquakes, volcanic eruptions, landslides, avalanches, subsidence, soil erosion); aquatic (floods, tidal waves, storm surges, tsunamis); biological (locusts, insect infestations, diseases such as bird flu and dengue).

A global effort — The UN General Assembly took up disasters in 1989; the World Conference on Natural Disaster Reduction at Yokohama, Japan (23–27 May 1994) adopted the Yokohama Strategy and Plan of Action for a Safer World, and 1990–2000 was declared the International Decade for Natural Disaster Reduction.

Earthquakes — key point 1? — The most unpredictable and destructive of all natural disasters; tectonic earthquakes are the most devastating.

Earthquakes — key point 2? — The Indian plate moves about one centimetre a year to the north and north-east and is blocked by the Eurasian plate. Energy builds up where they are locked and is released suddenly along the Himalayan arc.

Earthquakes — key point 3? — Most vulnerable: Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, the Darjeeling subdivision of West Bengal and all seven states of the north-east. Gujarat (1819, 1956, 2001) and Maharashtra (1967, 1993) have also had severe earthquakes.

Earthquakes — key point 4? — Some scientists link quakes in the old, stable Peninsula to a fault line along the Bhima (Krishna) near Latur and Osmanabad.

Earthquakes — key point 5? — From more than 1,200 past earthquakes India is divided into five zones, from very high to very low damage risk. The Very High zone includes the north-eastern states, the Bihar–Nepal border north of Darbhanga and Araria, Uttarakhand, western Himachal Pradesh (around Dharamshala), the Kashmir valley and the Kuchchh. The Deccan plateau is the safest.

Earthquakes — key point 6? — Mitigation: seismological monitoring centres and GPS, a vulnerability map and public awareness, suitable house designs, and making earthquake-resistant designs and light materials mandatory in vulnerable areas.

Earthquakes — Plate movement? — about 1 cm a year, north and north-east

Earthquakes — Zones? — five damage-risk zones

Tsunami — key point 1? — When an earthquake or eruption moves the sea floor suddenly, the displaced water rises in high waves — tsunamis (‘harbour waves’) or seismic sea waves.

Tsunami — key point 2? — Over deep water a tsunami has a long wavelength and small height — it lifts a ship only a metre or two. In shallow water the wavelength shrinks and the height grows, sometimes to 15 m or more.

Tsunami — key point 3? — The tsunami of 26 December 2004 killed more than 300,000 people. India then volunteered to join the International Tsunami Warning System.

Tsunami — Wave height near coast? — up to 15 m or more

Tsunami — 26 December 2004? — more than 300,000 deaths

Tropical cyclones — key point 1? — Intense low-pressure systems between 30°N and 30°S, 500–1,000 km across and 12–14 km high — heat engines powered by latent heat from ocean moisture.

Tropical cyclones — key point 2? — They need warm moist air, a strong Coriolis force (so none form within 0°–5° of the equator), an unstable troposphere and no strong vertical wind wedge.

Tropical cyclones — key point 3? — India’s cyclones form over the Bay of Bengal and the Arabian Sea; in the Bay of Bengal mostly in October and November. Coasts are struck by storms averaging 180 km/h, with a storm surge — an abnormal rise in sea level — that floods settlements and fields.

Tropical cyclones — key point 4? — Cyclones are more predictable in time and place than earthquakes; cyclone shelters, embankments, dykes, reservoirs and afforestation reduce damage.

Tropical cyclones — Size? — 500–1,000 km across, 12–14 km high

Tropical cyclones — Average wind on the coast? — 180 km/h

Floods — key point 1? — Floods happen when run-off exceeds what river channels can carry and spills onto the flood plains — also from storm surges, long intense rain, melting snow and silted channels. Deforestation, bad farming practices and settling on flood plains make them worse.

Floods — key point 2? — The Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares as flood-prone. Assam, West Bengal and Bihar are among the most flood-prone states; rivers in Punjab and Uttar Pradesh flood occasionally; Rajasthan, Gujarat, Haryana and Punjab now see flash floods; Tamil Nadu sometimes floods in November–January.

Floods — key point 3? — Floods leave fertile silt — Majuli in Assam, the largest riverine island in the world, grows good paddy after the Brahmaputra’s floods — but the losses far outweigh this.

Floods — key point 4? — Control: embankments, dams, afforestation, limiting building in the upper reaches, and clearing encroachments from river channels.

Floods — Flood-prone land? — 40 million hectares (Rashtriya Barh Ayog)

Droughts — key point 1? — A long shortage of water from too little rain, heavy evaporation and over-use of reservoirs and groundwater.

Droughts — key point 2? — Four kinds: meteorological (too little rain), agricultural (low soil moisture — an area with over 30% of its cropped area irrigated is not counted as drought-prone), hydrological (stored water falls below what rain can refill) and ecological.

Droughts — key point 3? — About 19% of India’s area and 12% of its people suffer drought every year; about 30% of the country is drought-prone, affecting around 50 million people.

Droughts — key point 4? — Extreme drought: most of Rajasthan west of the Aravali (Marusthali) and Kachchh; Jaisalmer and Barmer get under 90 mm of rain a year. Severe: eastern Rajasthan, most of Madhya Pradesh, eastern Maharashtra, interior Andhra Pradesh and the Karnataka plateau, and more.

Droughts — key point 5? — Drought brings akal (no grain), trinkal (no fodder), jalkal (no water) — and worst of all, trikal, all three at once. Remedies: safe water, fodder, finding aquifers, moving water from surplus areas, drought-resistant crops and rainwater harvesting.

Droughts — Drought-prone area? — about 30% of India

Droughts — Hit every year? — 19% of area, 12% of people

Landslides — key point 1? — The rapid sliding of large masses of bedrock — less dramatic than earthquakes or cyclones but just as costly, and controlled by very local factors, so hard to forecast.

Landslides — key point 2? — Very high vulnerability: young, unstable Himalayan and Andaman–Nicobar mountains, high-rainfall steep slopes of the Western Ghats and Nilgiris, the north-east, and areas of heavy road and dam building. High: all Himalayan states and the north-eastern states except the plains of Assam.

Landslides — key point 3? — Largely safe: Rajasthan, Haryana, Uttar Pradesh, Bihar, West Bengal (except Darjiling district), Assam (except Karbi Anglong) and the southern coastal regions. Mining and subsidence cause landslides in states such as Jharkhand, Odisha, Chhattisgarh and Madhya Pradesh.

Landslides — key point 4? — Mitigation: restrict roads, dams and large settlements on high-risk slopes, farm only valleys and moderate slopes, plant forests, build bunds, and encourage terrace farming where jhumming (shifting cultivation) is practised.

Disaster management: the three stages? — The Disaster Management Bill, 2005 defines a disaster as a catastrophe from natural or man-made causes, beyond the coping capacity of the affected community. Management has three stages: before (data, vulnerability maps, awareness, preparedness), during (rescue, evacuation, shelters, food, water, medical aid) and after (rehabilitation, recovery and capacity-building). About two-thirds of India’s area and people are vulnerable to disasters; the National Institute of Disaster Management was set up to help.