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Class 11 Natural Hazards and Disasters: cheat sheet
CBSE Social Science. How hazards become disasters, how they are classified, India’s earthquakes, floods, droughts, cyclones, tsunamis and landslides, and the stages of disaster management.
Key ideas
- A hazard becomes a disaster when it strikes suddenly and causes damage beyond people’s capacity to cope.
- Natural hazards are atmospheric (cyclones, droughts, blizzards), terrestrial (earthquakes, landslides), aquatic (floods, tsunamis) or biological.
- The Indian plate moves about 1 cm a year north and north-east against the Eurasian plate, so stress builds up and earthquakes strike the Himalayas and the north-east.
- Tropical cyclones form between about 30° N and 30° S but not within 5° of the equator, where the Coriolis force is absent; storm surges flood the coasts.
- Floods are made worse by deforestation, blocked drainage and settling on floodplains, though they also leave fertile silt.
- Droughts may be meteorological, agricultural, hydrological or ecological; rainwater harvesting and drought-resistant crops help.
- Disaster management has three stages: preparedness before, rescue and relief during, and rehabilitation after.
Remember
| Plate movement | 1 cm a year: metres = years ÷ 100 |
| Drought-prone rule | an area with over 30% of its gross cropped area irrigated is excluded |
| Flood-prone land | about 40 million hectares (National Flood Commission) |
| Share of an area | per cent × area ÷ 100 |
| Famine words | akal food grains; trinkal fodder; jalkal water; trikal all three |
| Yokohama Strategy | World Conference on disaster reduction, May 1994 |
Watch out
- Calling a tsunami atmospheric (it is aquatic) or a drought aquatic (it is atmospheric).
- Including a district with more than 30% irrigated area as drought-prone.
- Thinking tropical cyclones form right at the equator.
Worked example
Areas with more than 30 per cent of their gross cropped area irrigated are excluded from the drought-prone category. Is each district included or excluded? (a) 35% irrigated (b) 60% irrigated
Working: over 30%: excluded
Answer: (a) excluded (b) excluded
Practise Natural Hazards and Disasters
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