Master10
Disaster Management & Climate Resilience Module

Cyclones, Floods & Glacial Lake Outburst Floods

Hydro-meteorological disasters account for the largest proportion of climate-induced disruptions in India. Tropical cyclones originating in the Bay of Bengal and Arabian Sea are monitored by the India Meteorological Department (IMD) utilizing Doppler weather radars, INSAT satellite imagery, and a four-stage color-coded warning protocol (Green, Yellow, Orange, Red). Riverine flood management is spearheaded by the Central Water Commission (CWC), which operates a nationwide telemetry and flood forecasting network across major river basins. In high-altitude Himalayan catchments, climate change has accelerated glacial retreat, giving rise to vulnerable moraine-dammed glacial lakes susceptible to catastrophic Glacial Lake Outburst Floods (GLOFs). Mitigation strategies encompass early warning acoustic sensors, controlled siphoning, and integrated river basin planning.

Key Concepts & Examination Highlights

  • The India Meteorological Department (IMD) issues cyclone alerts via four color codes: Green (Normal), Yellow (Watch), Orange (Alert), and Red (Warning).
  • The Central Water Commission (CWC) operates over 300 flood forecasting stations across major Indian river basins.
  • South Lhonak Lake in Sikkim experienced a major Glacial Lake Outburst Flood (GLOF) in October 2023 following torrential rainfall.
  • The Integrated Coastal Zone Management (ICZM) project builds multi-purpose cyclone shelters along vulnerable coastlines.
  • Tropical cyclones in the North Indian Ocean are named sequentially from a rotating list contributed by 13 member nations of the WMO/ESCAP Panel on Tropical Cyclones.
  • Tropical cyclones require sea surface temperatures of at least 26.5°C, high atmospheric moisture, low vertical wind shear, and sufficient Coriolis force (usually >5° latitude from the equator) to develop.
  • The IMD classifies cyclonic disturbances by maximum sustained surface wind speed: Cyclonic Storm (62–88 km/h), Severe Cyclonic Storm (89–117 km/h), Very Severe (118–165 km/h), Extremely Severe (166–221 km/h), and Super Cyclone (>= 222 km/h).
  • The 1999 Odisha Super Cyclone was the deadliest tropical cyclone in recent Indian history, making landfall near Paradip with winds exceeding 260 km/h.
  • Glacial Lake Outburst Floods (GLOFs) occur when natural moraine or ice dams holding glacial meltwater breach suddenly due to avalanches, earthquakes, or excessive precipitation.
  • The Rashtriya Barh Ayog (National Flood Commission), established in 1976, identified roughly 40 million hectares of land in India as flood-prone.
  • The Urban Flood Management guidelines issued by NDMA emphasize integrated drainage network modeling, desilting of stormwater drains, and conservation of urban wetlands.
  • Doppler Weather Radars (DWRs) operated by the IMD provide real-time tracking of storm intensity, velocity, precipitation rate, and eye formation within a 400-km radius.
  • Tropical cyclones require warm sea surface temperatures of at least 26.5°C, significant Coriolis force, high middle-tropospheric humidity, and low vertical wind shear to form.
  • Tropical cyclones in the Northern Indian Ocean (Bay of Bengal and Arabian Sea) are named by the WMO/ESCAP Panel on Tropical Cyclones comprising 13 member countries.
  • The storm surge is an abnormal rise of sea level generated by atmospheric low pressure and severe onshore hurricane-force winds, causing the majority of cyclone fatalities.
  • Flash floods are sudden, high-velocity inundations caused by intense localized rainfall (cloudbursts), dam breaks, or sudden release of water from glacial impoundments.
  • Glacial Lake Outburst Floods (GLOFs) occur when a moraine-dammed or ice-dammed glacial lake breaches abruptly due to avalanches, earthquakes, or hydrostatic pressure.
  • The South Lhonak Lake GLOF in Sikkim in October 2023 caused catastrophic flash flooding along the Teesta River basin and destroyed the Chungthang Dam.
  • The Central Water Commission (CWC) operates a nationwide hydrological observation and flood forecasting network issuing level-based and inflow forecasts across major river basins.
  • The India Meteorological Department (IMD) utilizes Doppler Weather Radars (DWR) and INSAT satellites for real-time tracking, landfall prediction, and intensity estimation of tropical cyclones.
  • The National Cyclone Risk Mitigation Project (NCRMP), assisted by the World Bank, constructs multi-purpose cyclone shelters, saline embankments, and early warning dissemination systems in coastal states.
  • Urban flooding differs from rural riverine flooding due to rapid impervious surface runoff, inadequate storm-water drainage capacity, and severe encroachment on natural wetlands.
  • Flood Plains Zoning involves land-use regulation across floodplains to demarcate prohibited, restricted, and regulated zones based on flood frequency curves.
  • Cloudbursts represent intense precipitation exceeding 100 mm per hour over a localized geographical area of approximately 20 to 30 km², frequent in Himalayan valleys.
  • The Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, operates the Indian Tsunami Early Warning Centre (ITEWC) and Ocean State Forecast (OSF) systems.
  • Tropical cyclones in the North Indian Ocean basin develop over the Bay of Bengal and the Arabian Sea, with a typical ratio of 4:1 in favor of the Bay of Bengal.
  • The Indian Meteorological Department (IMD) is the official Regional Specialized Meteorological Centre (RSMC) designated by the WMO for cyclone forecasting in the North Indian Ocean.
  • Tropical cyclones are categorized based on maximum sustained surface wind speed (MSW): Depression (31-50 km/h), Deep Depression (51-62 km/h), and Cyclonic Storm (63-88 km/h).
  • Severe Cyclonic Storms have wind speeds of 89-117 km/h; Very Severe Cyclonic Storms span 118-166 km/h; Extremely Severe Cyclonic Storms reach 167-221 km/h.
  • A Super Cyclonic Storm is defined as a tropical cyclone with maximum sustained wind speeds exceeding 222 km/h (120 knots).
  • The 1999 Odisha Super Cyclone (October 29, 1999) was one of the deadliest cyclones in modern Indian history, making landfall near Paradip with winds exceeding 260 km/h.
  • Tropical cyclone naming in the North Indian Ocean is coordinated by a panel of 13 member countries (including India, Bangladesh, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, and Thailand).
  • Storm surge is the abnormal rise of sea level generated by a cyclone's low atmospheric pressure and strong onshore winds, causing the majority of coastal cyclone casualties.
  • The 4-stage cyclone warning system used by the IMD comprises Pre-Cyclone Watch (72 hours prior), Cyclone Alert (Yellow, 48 hours prior), Cyclone Warning (Orange, 24 hours prior), and Post-Landfall Outlook (Red, 12 hours prior).
  • Cyclone Phailin (2013) and Cyclone Fani (2019) demonstrated India's successful zero-casualty evacuation protocols, evacuating over 1 million people within 48 hours in Odisha.
  • Cyclone Amphan (May 2020) was the first Super Cyclonic Storm to form in the Bay of Bengal since 1999, striking West Bengal and Bangladesh.
  • Cyclone Biparjoy (June 2023) was an extremely severe cyclonic storm with one of the longest lifespans over the Arabian Sea, making landfall near Jakhau Port in Gujarat.
  • Doppler Weather Radars (DWRs) provide continuous surveillance of cyclonic wind fields, cloud structures, and precipitation within a 400 km radius.
  • Floods in India are caused primarily by intense monsoon downpours, riverbed siltation, flash floods, dam breaches, and drainage congestion in urban areas.
  • Approximately 40 million hectares of land in India (about 12 percent of total geographical area) is prone to recurring floods according to the Rashtriya Barh Ayog (National Flood Commission).
  • The Rashtriya Barh Ayog (RBA) was constituted in 1976 under the Ministry of Agriculture and Irrigation to formulate comprehensive national flood management guidelines.
  • The Ganga basin (especially eastern UP, Bihar, and West Bengal) and the Brahmaputra basin (Assam) are the most flood-affected river basins in India.
  • The Brahmaputra River experiences severe annual flooding and extensive bank erosion due to heavy monsoons, high sediment load, and steep gradient from the Himalayas.
  • Urban Flooding is a distinct disaster caused by high-intensity localized rainfall exceeding the hydraulic capacity of stormwater drains due to rapid concretization and wetland loss.
  • The 2005 Mumbai floods (over 944 mm rain in 24 hours) and 2015 Chennai floods highlighted the vulnerability of unplanned urban development and choked drainage channels.
  • The National Disaster Management Authority (NDMA) issued dedicated Guidelines for Management of Urban Flooding in 2010, recognizing urban flooding as a separate disaster category.
  • The Central Water Commission (CWC) operates a nationwide flood forecasting network of over 330 hydrometric stations, issuing daily flood bulletins and level forecasts.
  • Structural flood mitigation measures include construction of embankments, flood walls, multi-purpose storage reservoirs, channel improvements, and detention basins.
  • Non-structural flood mitigation measures include Flood Plain Zoning, watershed management, real-time early warning systems, disaster insurance, and community flood preparedness.
  • Flood Plain Zoning regulates land use along river floodplains into prohibited, restricted, and warning zones to minimize flood damage.
Curriculum & Reference Sources: India Meteorological Department (IMD), Central Water Commission (CWC), Geological Survey of India (GSI).

Sample Solved Questions & Concept Explanations

8 Verified Concept Questions
Q1.EASY

Which color alert in the India Meteorological Department's (IMD) cyclone warning protocol indicates 'Take Action' / Extreme Weather Warning?

Q2.MEDIUM

What scientific term describes a sudden, high-discharge flood caused by the catastrophic failure of a moraine or ice dam containing a glacial lake in high-altitude mountain environments?

Q3.HARD

In October 2023, a catastrophic Glacial Lake Outburst Flood (GLOF) caused widespread devastation and breached the Chungthang Dam in Sikkim following the breach of which high-altitude lake?

Q4.EASY

What does a 'Yellow Alert' in the India Meteorological Department's (IMD) colour-coded weather warning system signify?

Q5.EASY

What action is indicated by an 'Orange Alert' issued by the India Meteorological Department (IMD) during cyclone or heavy monsoon events?

Q6.EASY

In which direction do winds rotate around the low-pressure center of a tropical cyclone in the Northern Hemisphere (including the Bay of Bengal and Arabian Sea)?

Q7.EASY

What is the roughly circular, calm, cloudless, and lowest-pressure central region of a mature tropical cyclone called?

Q8.EASY

Which advanced radar technology deployed along Indian coastlines by IMD measures both rainfall intensity and wind velocity inside storm clouds up to 400–500 km away?