Natural Hazards and Disasters
1. Learning Objectives
After reading these notes, you will be able to:
2. Introduction
📌 Natural Hazard vs Natural Disaster — Key Difference
🔵 Natural Hazard
Elements or circumstances in the natural environment that have the potential to cause harm to people or property. May be swift or permanent. Example: steep Himalayan slopes, extreme desert climate, ocean currents.
🔴 Natural Disaster
Relatively sudden event that causes large-scale, widespread death, loss of property and social disruption over which people have little or no control. A hazard becomes a disaster when the magnitude of damage is very high.
- Disasters are not only caused by natural forces — human activities also cause or intensify disasters. Examples: Bhopal Gas Tragedy, Chernobyl nuclear disaster, deforestation causing landslides and floods.
- Human-made disasters have increased in number and magnitude over the years.
- Natural disasters: best approach is mitigation and management (not prevention).
- Important global efforts: Earth Summit, Rio de Janeiro (1993); World Conference on Disaster Management, Yokohama, Japan (May 1994) → adopted Yokohama Strategy.
- Decade 1990–2000 declared as International Decade for Natural Disaster Reduction (IDNDR).
3. Classification of Natural Disasters
4. Earthquakes
- Most vulnerable states: J&K, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, Darjeeling (WB), and all 7 northeastern states.
- In Peninsular India: Gujarat (1819, 1956, 2001) and Maharashtra (1967 Koyna, 1993 Latur) — explained by fault line along river Bhima (Krishna) near Latur and Osmanabad.
📌 Five Earthquake Zones of India
| Zone | Risk Level | Areas |
|---|---|---|
| I | Very High Damage Risk | NE states, North of Darbhanga & Araria (Bihar–Nepal border), Uttarakhand, W. Himachal Pradesh, Kashmir Valley, Kachchh (Gujarat) |
| II | High Damage Risk | Remaining J&K & Ladakh, Himachal Pradesh, N. Punjab, E. Haryana, Delhi, W. Uttar Pradesh, N. Bihar |
| III | Moderate Damage Risk | — |
| IV | Low Damage Risk | — |
| V | Very Low Damage Risk | Most parts of Deccan Plateau (most stable area) |
⚠️ Effects of Earthquakes
On Ground
Fissures, Cracking, Slidings, Landslides, Liquefaction, Earth pressure
On Man-made Structures
Overturning, Buckling, Collapse of settlements, roads, bridges, industries
On Water
Hydro-dynamic pressure, Tsunami waves, Reservoir formation due to river blockage
Other Effects
Surface fissures → water gushes out. Landslides block rivers. Rivers change course → floods. Renders people homeless.
🛡️ Earthquake Hazard Mitigation
- Establish seismological centres for regular monitoring. Use GPS to monitor tectonic plate movements.
- Prepare vulnerability maps and educate people about risk zones.
- Modify building designs in vulnerable areas — no high-rise buildings, large industries or big cities in earthquake zones.
- Make it mandatory to use earthquake-resistant designs and light materials in construction.
5. Tsunami
- After initial disturbance, a series of afterwaves oscillate between high crest and low trough to restore water level.
- Speed of wave depends on depth of water — faster in shallow water than in deep ocean.
- Over deep ocean: very long wave-length, limited height (~1–2 m) → hard to detect. Ship hardly affected.
- Near coast (shallow water): wave-length decreases, height increases → can reach up to 15 m or more → massive destruction along shores. Also called Shallow Water Waves.
- Most frequent along Pacific Ring of Fire — Alaska, Japan, Philippines, SE Asia, Indonesia, Myanmar, Sri Lanka, India.
- 26 December 2004 Tsunami: More than 3,00,000 people died. India joined International Tsunami Warning System after this disaster.
6. Tropical Cyclone
📌 Conditions for Formation of a Tropical Cyclone
- Large and continuous supply of warm and moist air to release enormous latent heat.
- Strong Coriolis force to prevent filling of low pressure at centre. (No Coriolis force near equator → no cyclone between 0°–5° latitude.)
- Unstable conditions through the troposphere that create local disturbances.
- Absence of strong vertical wind wedge (which disturbs vertical transport of latent heat).
🌏 Cyclones in India
- Cyclones originate in Bay of Bengal (east) and Arabian Sea (west) due to India’s peninsular shape.
- Bay of Bengal cyclones: mostly during October–November; originate between 16°–2°N latitudes, west of 92°E.
- By July, origin shifts to ~18°N latitude, west of 90°E near Sunderbans Delta.
- Coastal areas hit by cyclones with average velocity of 180 km/h → abnormal rise in sea level = Storm Surge.
- Cyclone force decreases with distance from sea → interior areas less affected.
7. Floods
📌 Causes of Floods
- Surface run-off exceeds river channel capacity
- Storm surge in coastal areas
- High intensity rainfall for a long period
- Melting of ice and snow
- Reduction in infiltration rate
- Heavy soil erosion adding material to water
- Human causes: Deforestation, unscientific agriculture, blocking natural drainage, colonisation of flood plains and river-beds
🗺️ Flood-Prone Areas in India
- Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares as flood-prone in India.
- High flood-prone states: Assam, West Bengal, Bihar
- Occasional floods: Punjab, Uttar Pradesh
- Flash floods in recent decades: Rajasthan, Gujarat, Haryana, Punjab
- Tamil Nadu: flooding in November–January due to retreating monsoon
⚖️ Consequences of Floods
❌ Negative Effects
Destroys crops; damages roads, rails, bridges; millions rendered homeless; cattle washed away; spread of cholera, gastro-enteritis, hepatitis and waterborne diseases
✅ Positive Effects
Deposits fertile silt on agricultural fields (good for crops). Majuli Island (Assam) — largest riverine island in world — gives good paddy crops after Brahmaputra floods
🛡️ Flood Control Measures
- Construction of flood protection embankments in flood-prone areas
- Construction of dams
- Afforestation and discouraging construction in upper reaches of flood-causing rivers
- Remove human encroachment from river channels and depopulate flood plains
- Cyclone centres for relief in coastal areas hit by storm surge
8. Droughts
📋 Four Types of Droughts
☀️ Meteorological Drought
Prolonged period of inadequate rainfall with mal-distribution over time and space.
🌾 Agricultural Drought
Also called Soil Moisture Drought. Low soil moisture → crop failure. If >30% of gross cropped area is irrigated → excluded from drought-prone category.
💧 Hydrological Drought
Water level in aquifers, lakes, reservoirs falls below what precipitation can replenish.
🌿 Ecological Drought
Productivity of a natural ecosystem fails due to water shortage → ecological distress and damage to ecosystem.
🗺️ Drought Prone Areas in India
| Category | Areas |
|---|---|
| Extreme Drought | Most of Rajasthan (west of Aravali — Marusthali), Kachchh (Gujarat), Jaisalmer and Barmer districts (less than 90 mm rainfall) |
| Severe Drought Prone | Eastern Rajasthan, most of Madhya Pradesh, eastern Maharashtra, interior Andhra Pradesh, Karnataka Plateau, N. interior Tamil Nadu, S. Jharkhand, interior Odisha |
| Moderate Drought | N. Rajasthan, Haryana, S. Uttar Pradesh, remaining Gujarat, Maharashtra (except Konkan), Jharkhand, Coimbatore plateau (TN), interior Karnataka |
⚠️ Consequences of Drought
- Akal (scarcity of food grains), Trinkal (fodder shortage), Jalkal (water shortage), Trikal (all three combined) — most devastating
- Large-scale death of cattle; migration of humans and livestock
- Contaminated water → gastro-enteritis, cholera, hepatitis
🛡️ Drought Mitigation Measures
- Immediate: Safe drinking water distribution, medicines, fodder and water for cattle, shifting people to safer places
- Long-term: Identify groundwater potential (aquifers); inter-linking of rivers; construction of reservoirs and dams
- Remote sensing and satellite imagery to identify river basins for inter-linking and groundwater potential
- Promote drought-resistant crops and train farmers
- Rainwater harvesting — effective method to minimise drought effects
9. Landslides
🗺️ Landslide Vulnerability Zones in India
| Zone | Areas |
|---|---|
| Very High Vulnerability | Young mountainous areas of Himalayas and Andaman & Nicobar; high rainfall regions with steep slopes in Western Ghats and Nilgiris; northeastern regions; earthquake-prone areas; areas of intense construction (roads, dams) |
| High Vulnerability | All Himalayan states and northeastern states except plains of Assam |
| Moderate to Low | Trans-Himalayan areas (Ladakh, Spiti); Aravali; rain-shadow areas of Western and Eastern Ghats; Deccan plateau. Mining-related landslides in Jharkhand, Odisha, Chhattisgarh, MP, Maharashtra, AP, Karnataka, TN, Goa, Kerala |
| Safe Areas | Rajasthan, Haryana, UP, Bihar, West Bengal (except Darjiling), Assam (except Karbi Anglong), coastal regions of southern states |
⚠️ Consequences of Landslides
- Relatively small and localised direct influence but far-reaching consequences
- Roadblock, destruction of railway lines, channel-blocking due to rock-falls
- Diversion of river courses → floods and loss of life
- Makes spatial interaction difficult, risky and costly → adversely affects developmental activities
🛡️ Mitigation
- Restrict construction of roads, dams and other developmental activities in high vulnerability zones
- Limit agriculture to valleys and moderate slopes
- Control development of large settlements in high vulnerability zones
- Promote large-scale afforestation and construction of bunds to reduce water flow
- Encourage Terrace Farming in northeastern hill states (instead of Jhumming/Shifting cultivation)
10. Disaster Management
Pre-Disaster Management
Generating data and information about disasters · Preparing vulnerability zoning maps · Spreading awareness · Disaster planning, preparedness and preventive measures
During Disaster
Rescue and relief operations · Evacuation · Construction of shelters and relief camps · Supplying water, food, clothing and medical aids on emergency basis
Post-Disaster
Rehabilitation and recovery of victims · Capacity-building to cope with future disasters
National Institute of Disaster Management (NIDM) — established for research, training and capacity building.
Cyclone management: Construction of cyclone shelters, embankments, dykes, reservoirs and afforestation to reduce wind speed.
Summary — Quick Revision
Hazard = potential to cause harm. Disaster = sudden event causing large-scale damage. 4 categories: Atmospheric · Terrestrial · Aquatic · Biological.
Indian plate moves 1 cm/year northward → blocked by Eurasian plate → energy builds up → earthquake along Himalayan arch.
India has 5 earthquake zones. Zone I (Very High Risk): NE states, Uttarakhand, Kashmir, Kachchh. Zone V (Very Low): Deccan Plateau.
Tsunami = seismic sea waves caused by sea-floor movement. Over deep ocean: undetectable (1–2 m). Near coast: can reach 15 m+. 2004 Tsunami = 3,00,000+ deaths.
Cyclone = intense low pressure between 30°N–30°S. Energised by latent heat. India’s Bay of Bengal cyclones mostly in Oct–Nov. Storm surge = abnormal sea level rise.
Flood-prone: Assam, West Bengal, Bihar (river floods); coastal AP, Odisha, TN, Gujarat (cyclone); Punjab, Rajasthan, Haryana (flash floods). Flood-prone area = 40 million hectares.
4 types of drought: Meteorological · Agricultural (Soil Moisture) · Hydrological · Ecological. 19% area, 12% population affected by drought every year.
Extreme drought: Rajasthan (west of Aravali), Kachchh. Drought effects: Akal (food) + Trinkal (fodder) + Jalkal (water) = Trikal.
Landslide very high vulnerability: Himalayas, A&N Islands, Western Ghats, NE India. Mitigation: restrict construction, afforestation, terrace farming instead of Jhumming.
Disaster management: 3 stages — Pre-disaster (awareness, vulnerability maps) → During (rescue, relief) → Post-disaster (rehabilitation, capacity-building). Disaster Management Bill 2005 passed.
Important Terms to Remember
- Natural Hazard: Elements in the natural environment with the potential to cause harm — may be swift or permanent (e.g., steep slopes, ocean currents, extreme climate).
- Natural Disaster: Sudden, large-scale event causing widespread death, property loss and social disruption over which people have little or no control.
- Tsunami: High vertical waves caused by sudden sea-floor movement due to earthquakes or volcanic eruptions. Also called Seismic Sea Waves or Shallow Water Waves.
- Storm Surge: Abnormal rise in sea level caused when a tropical cyclone drives sea water onto land with strong winds and heavy rain.
- Tropical Cyclone: Intense low-pressure system between 30°N–30°S with high-velocity winds. Energised by latent heat from warm moist ocean air.
- Meteorological Drought: Prolonged period of inadequate rainfall.
- Agricultural Drought: Insufficient soil moisture to support crops → crop failure. Also called Soil Moisture Drought.
- Hydrological Drought: Water levels in aquifers, lakes and reservoirs fall below what precipitation can replenish.
- Ecological Drought: Natural ecosystem productivity fails due to water shortage.
- Akal / Trinkal / Jalkal / Trikal: Sanskrit terms for scarcity of food grains / fodder / water / all three together — used in context of drought consequences.
- IDNDR: International Decade for Natural Disaster Reduction (1990–2000), declared at Yokohama Conference.
- Yokohama Strategy (1994): Plan of Action for a Safer World, adopted at World Conference on Natural Disaster Reduction, Yokohama, Japan.
- Rashtriya Barh Ayog: National Flood Commission — identified 40 million hectares as flood-prone in India.
- Jhumming: Slash and Burn / Shifting cultivation practiced in northeastern hill states — contributes to landslides.
- Terrace Farming: Cutting step-like levels on hillsides to grow crops — helps prevent soil erosion and landslides.