Natural Hazards & Vulnerability Mapping — Seismic Zones, Flood Maps & Risk Assessment

Overview

India is among the world's most disaster-prone countries — approximately 59% of its landmass is vulnerable to earthquakes, 40 million hectares are flood-prone, 68% of net sown area is drought-vulnerable, and ~12.6% of land area is landslide-prone. Understanding the spatial distribution of natural hazards, the agencies responsible for mapping them, and the vulnerability assessment frameworks is essential for both GS1 (Physical Geography) and GS3 (Disaster Management).

Global Seismic Belts

Major Earthquake Zones of the World

For Prelims: Ring of Fire = ~90% of world's earthquakes; Alpide Belt = ~17% of world's largest earthquakes. India lies in the Alpide Belt — the Himalayan zone is one of the most seismically active continental collision zones on Earth.

Seismic Zones of India

BIS Seismic Zonation

The Bureau of Indian Standards (BIS) divides India into seismic zones based on the Modified Mercalli Intensity (MMI) scale and historical earthquake data. The zonation is used for earthquake-resistant building design codes.

Traditional Classification (IS 1893)

Area Distribution

For Prelims: ~59% of India's landmass is in Zone III or above (moderate to very high risk). Zone V covers the entire Northeast, Kashmir Valley, Kutch, and Andaman and Nicobar Islands. Delhi is in Zone IV.

Updated Seismic Zonation (BIS, 2025)

In 2025, the BIS released an updated earthquake design code introducing a new Zone VI (Super-Critical) covering the entire Himalayan arc. Key changes:

Major Earthquakes in India

For Mains: The Latur earthquake (1993) is a landmark event — it occurred in what was then Zone I (lowest risk), demonstrating that peninsular India is NOT immune to earthquakes. This led to the abolition of Zone I and the reclassification of the entire country into Zones II–V. It also catalysed the creation of the National Disaster Management Authority (NDMA) framework.

Flood-Prone Areas of India

Scale of the Problem

Major Flood-Prone Basins

Causes of Flooding in India

Cyclone Tracks in India

Bay of Bengal vs Arabian Sea

IMD Cyclone Classification

For Prelims: IMD classifies cyclones into 7 categories (depression to super cyclonic storm). Cyclones are named at the "Cyclonic Storm" stage (62–88 km/h). The Bay of Bengal generates 4–5 times more cyclones than the Arabian Sea. The Super Cyclone of 1999 (Odisha) was the deadliest in recent Indian history.

Landslide Vulnerability

Scale in India

Vulnerable Regions

Triggering Factors

GSI Mapping and Early Warning

Drought-Prone Areas

Scale of Drought Vulnerability

Major Drought-Prone Regions

NRSC and ISRO in Drought Mapping

GLOF (Glacial Lake Outburst Flood)

For Mains: GLOFs represent the intersection of climate change and disaster risk. The Sikkim GLOF (2023) demonstrated the cascading nature of these events — a glacial lake breach destroyed a hydropower dam downstream, raising questions about the environmental clearance of infrastructure projects in GLOF-prone Himalayan zones.

Multi-Hazard Vulnerability Mapping

BMTPC Vulnerability Atlas of India

NDMA's Role

ISRO/NRSC in Hazard Mapping

Multi-Hazard Approach

UPSC Relevance

Prelims Focus Areas

• India: ~59% landmass earthquake-prone; Zone V = NE India, Kashmir, Kutch, A&N
• Zone II = lowest risk; Zone V = highest risk (traditional); Zone VI introduced 2025
• Flood-prone area: 40 million hectares; worst basins = Brahmaputra, Ganga
• Drought: 68% of net sown area vulnerable; 13 states
• Landslide: 12.6% of land area (~4.3 lakh sq. km); GSI mapping; NW Himalayas most prone
• Ring of Fire = ~90% of world's earthquakes; Alpide Belt = second most active
• IMD cyclone classification: 7 categories (depression to super cyclonic storm)
• Bay of Bengal: 4–5 times more cyclones than Arabian Sea
• BMTPC: Vulnerability Atlas of India (first edition 1997, third edition 2019)
• GLOF: South Lhonak Lake, Sikkim, 2023; ~7,500 glacial lakes in Indian Himalayas
• Latur earthquake (1993): led to abolition of Zone I

Mains Focus Areas

• Multi-hazard vulnerability of India — why India is uniquely disaster-prone (tectonic setting, monsoon climate, diverse topography)
• Seismic risk in the Himalayas — implications for hydropower, infrastructure, urbanisation
• Flood management: structural (dams, embankments) vs non-structural (floodplain zoning, early warning, insurance) approaches
• GLOF as a climate-disaster nexus — infrastructure development in Himalayan GLOF zones
• Drought management: rainfall dependency, irrigation gaps, and the role of remote sensing (NRSC, NADAMS)
• Cyclone preparedness: India's improvement in cyclone management (zero-casualty approach) — comparing 1999 Super Cyclone (10,000 deaths) with Cyclone Fani (2019, 64 deaths) and Amphan (2020, 98 deaths)
• Role of ISRO/NRSC, GSI, IMD, CWC, BMTPC, and NDMA in hazard mapping and early warning
• Landslide risk and the development-environment balance in hill states

Vocabulary

Moraine

• Pronunciation: /məˈreɪn/
• Definition: A mass of rocks, sediment, and debris deposited by a glacier at its edges (lateral moraine), at its terminus (terminal moraine), or beneath it (ground moraine) — terminal moraines often form natural dams that impound glacial lakes, making them critical to GLOF hazard assessment.
• Origin: From French moraine, possibly from Savoyard dialect morena ("mound of earth"); first used in geological literature in the 18th century to describe the ridges of debris observed at the margins of Alpine glaciers.

Seismic Zonation

• Pronunciation: /ˈsaɪzmɪk zoʊˈneɪʃən/
• Definition: The division of a region into zones of varying earthquake risk based on historical seismicity, tectonic setting, geological conditions, and probabilistic hazard analysis, used to determine building design codes and land-use planning standards for earthquake-resistant construction.
• Origin: From Greek seismos (σεισμός, "earthquake, shaking") + English zonation (from Greek zone, "belt, girdle"); in India, seismic zonation is governed by BIS code IS 1893, first published in 1962 and most recently updated in 2025 with the introduction of Zone VI.

Vulnerability Atlas

• Pronunciation: /ˌvʌlnərəˈbɪlɪti ˈætləs/
• Definition: A comprehensive cartographic document that maps the spatial distribution of natural hazard risks — earthquakes, cyclones, floods, landslides — across a country or region, using historical data, geological analysis, and remote sensing to assess the vulnerability of buildings, infrastructure, and populations.
• Origin: Vulnerability from Late Latin vulnerabilis ("capable of being wounded"), from vulnerare ("to wound"); atlas from Greek mythology — Atlas, the Titan who held up the sky, whose image appeared on the cover of Gerardus Mercator's 1595 book of maps, giving the word its modern meaning.

Key Terms

Ring of Fire

• Pronunciation: /rɪŋ ɒv ˈfaɪər/
• Definition: A horseshoe-shaped belt of intense seismic and volcanic activity stretching approximately 40,000 km around the margins of the Pacific Ocean, from New Zealand through Indonesia, Japan, Kamchatka, Alaska, and down the western coasts of North and South America to Chile — accounting for approximately 90% of the world's earthquakes and 75% of its active volcanoes.
• Context: The Ring of Fire is formed by subduction zones where oceanic plates (Pacific, Nazca, Philippine Sea) plunge beneath continental plates, generating earthquakes and magma that fuels volcanic eruptions; India does NOT lie in the Ring of Fire but in the Alpide (Mediterranean-Himalayan) Belt.
• UPSC Relevance: GS1 (Physical Geography). Prelims: Ring of Fire = ~90% of world's earthquakes; ~40,000 km; surrounds the Pacific; India is in the Alpide Belt, not the Ring of Fire. Mains: asked to compare the two global seismic belts and discuss India's tectonic vulnerability in the Himalayan collision zone.

GLOF (Glacial Lake Outburst Flood)

• Pronunciation: /dʒiː ɛl oʊ ɛf/
• Definition: A sudden and catastrophic release of water from a glacial lake when its moraine or ice dam is breached by an earthquake, avalanche, landslide, or excessive meltwater inflow, sending a destructive flood of water, sediment, and debris downstream — a growing hazard in the Himalayas due to climate-change-driven glacier retreat.
• Context: India has approximately 7,500 glacial lakes across 11 Himalayan river basins, of which 189–195 have been identified as having high GLOF potential; the South Lhonak Lake GLOF in Sikkim (October 2023) breached a moraine dam, destroyed the Chungthang Dam downstream, and killed 40+ people — highlighting the cascading risk of hydropower infrastructure in GLOF-prone zones.
• UPSC Relevance: GS1 (Physical Geography), GS3 (Disaster Management, Climate Change). Prelims: definition; South Lhonak Lake GLOF (2023, Sikkim); ISRO/NRSC monitoring role. Mains: asked to discuss GLOFs as a climate-disaster nexus — the tension between Himalayan hydropower development and GLOF risk; the role of satellite monitoring and early warning systems; and NDMA's mitigation strategies.

Sources: BIS (IS 1893 — Seismic Zonation), NDMA (ndma.gov.in), GSI (Geological Survey of India — Landslide Hazard Zonation, bhusanket.gsi.gov.in), NRSC/ISRO (Bhuvan, Flood Atlas, GLOF monitoring), BMTPC (Vulnerability Atlas of India), CWC (Central Water Commission), IMD (Cyclone Classification), National Flood Commission, pib.gov.in