Hydro-meteorological Disasters: Floods, Cyclones, Droughts, Heatwaves and Cloudbursts

Floods

Extent: India loses on average about 1,600 lives a year to floods. The Rashtriya Barh Ayog (1980) estimated the flood-prone area at 40 million hectares.

Causes:

• natural: heavy monsoon rainfall, cyclones, cloudbursts, glacial lake outbursts, and silted, meandering rivers (Brahmaputra, Kosi);
• human: encroachment on floodplains, deforestation, poor drainage, poorly managed dam releases (Kerala 2018 was debated), and urbanisation that turns land into concrete.

Urban floods have hit Mumbai (2005), Chennai (2015, 2023), Bengaluru (2022) and Delhi (2023). They are caused by clogged drains, lost lakes and wetlands, and extreme rainfall. The NDMA guidelines on urban flooding (2010) ask for drainage master plans and Doppler radar coverage.

Glacial Lake Outburst Floods (GLOFs): for example, South Lhonak in Sikkim (October 2023), which damaged the Chungthang dam. The NDMA has a GLOF risk mitigation programme for high-risk lakes.

Management:

• structural: embankments, dams, reservoirs and channel improvement;
• non-structural: flood plain zoning (a model bill from 1975, adopted by few states), flood forecasting by the Central Water Commission (over 300 stations), insurance and evacuation plans;
• the Flood Management and Border Areas Programme.

Cyclones

Formation: tropical cyclones need:

• sea surface temperature above 26.5 °C;
• the Coriolis force, so they do not form at the equator;
• low vertical wind shear;
• a pre-existing disturbance.

Indian seasons: cyclones are most frequent in pre-monsoon (April–June) and post-monsoon (October–December). The Bay of Bengal gets more cyclones than the Arabian Sea, roughly 4:1. However, the Arabian Sea is seeing more intense cyclones as it warms, for example Tauktae (2021) and Biparjoy (2023).

IMD classification by wind speed: depression, deep depression, cyclonic storm, severe, very severe, extremely severe, and super cyclonic storm (≥ 222 km/h).

Naming: the WMO/ESCAP Panel of 13 countries names North Indian Ocean cyclones. RSMC New Delhi (IMD) issues the names from a list adopted in 2020.

Odisha's success: deaths fell from about 10,000 in 1999 to a few dozen in Phailin (2013) and Fani (2019). This came from:

• early warning;
• mass evacuation (over a million people);
• cyclone shelters (the National Cyclone Risk Mitigation Project, with World Bank support);
• community volunteers;
• the Odisha State Disaster Management Authority, created in 1999 as the first in India.

The UN praised this "zero casualty" approach.

Droughts

Types:

• meteorological: rainfall more than 25% below normal;
• hydrological: depleted surface and ground water;
• agricultural: soil moisture inadequate for crops;
• socio-economic.

Indicators (Manual for Drought Management, 2016, revised 2020): rainfall deviation, the Standardised Precipitation Index, vegetation indices (NDVI), sown area, soil moisture and reservoir levels. States declare droughts.

Drought-prone regions: Rajasthan, the Deccan rain shadow (Marathwada, North Karnataka, Rayalaseema), Bundelkhand and Kalahandi.

Management:

• watershed development (PMKSY-Watershed);
• micro-irrigation;
• crop diversification away from water-intensive crops;
• MGNREGA water works;
• PMFBY insurance;
• contingency crop plans (ICAR);
• the Drought-Prone Areas Programme and Desert Development Programme (now merged).

Heatwaves

IMD criteria:

• maximum temperature at least 40 °C in the plains, 37 °C on the coast, or 30 °C in the hills; and
• a departure from normal of 4.5–6.4 °C (heatwave) or above 6.4 °C (severe heatwave);
• or an absolute 45 °C (heatwave) or 47 °C (severe).

Trends: heatwaves are rising in frequency and duration. Examples are 2022 and 2024, when Delhi recorded about 50 °C at some stations, with heatstroke deaths and electricity demand peaks.

Heat Action Plans:

• Ahmedabad (2013) was the first;
• NDMA guidelines (2016, revised 2019);
• heat action plans now exist in over 23 states and many cities.

They include early warnings, cooling centres, changes to working hours, cool roofs, water points and hospital preparedness. Heatwaves are not a notified disaster for SDRF funds, though states may use a share for local disasters, and inclusion is debated.

Cloudbursts and landslides

Cloudbursts: IMD defines a cloudburst as 100 mm or more of rain in an hour over about 20–30 km². They are common in the Himalaya, for example Kedarnath 2013 and Himachal 2023. Climate change and fragile slopes increase the risk.

Landslides are covered in the next lesson.

Lightning

Lightning is among the largest killers of the natural hazards in India, causing about 2,500–2,900 deaths a year. It is not a notified disaster nationally, though some states treat it as a local disaster. Early warning apps (Damini) and lightning arresters can help.

Early warning

• IMD: impact-based forecasts and colour codes (green, yellow, orange, red), Doppler radars, and Mission Mausam (2024).
• INCOIS: tsunami and ocean warnings.
• CWC: floods.
• CAP-based SACHET platform: SMS and cell broadcast alerts.

Common prelims traps

• Cyclones need SST above 26.5 °C and cannot form near the equator, where there is no Coriolis force.
• The Bay of Bengal has more cyclones, but the Arabian Sea cyclones are intensifying.
• A cloudburst is about 100 mm per hour.
• Heatwaves are judged on both absolute and departure-from-normal criteria.

Quick self-test

1. *Why has Odisha's cyclone death toll fallen sharply?* Early warning, evacuation, shelters and community preparedness.
2. *Name two human causes of urban floods.* Encroachment on lakes and drains, and impervious surfaces.
3. *What is a GLOF?* A sudden flood when a glacial lake's moraine dam breaches.

Practice: Mains question

*"Disasters are increasingly a product of development choices rather than nature alone." Discuss with reference to urban floods and heatwaves in India. (250 words)*

Key terms

• Storm surge: an abnormal rise in sea level pushed ashore by cyclone winds. It is the biggest killer in cyclones, especially along shallow coasts such as the head of the Bay of Bengal.
• Flash flood: a rapid flood within hours of intense rain, common in hilly terrain.
• Impact-based forecasting: a forecast that says what the weather will do (for example, which roads will flood), not just what it will be.
• Wet-bulb temperature: combines heat and humidity. Values near 35 °C are dangerous for human survival, and humid coastal cities face rising risk.
• Urban heat island: cities are warmer than their surroundings because of concrete, a lack of vegetation and waste heat.

Analysis: climate change and hydro-met hazards

The IPCC and IMD studies point to:

• more frequent extreme rainfall events in central India;
• rapid intensification of cyclones;
• longer, hotter heatwave seasons;
• more variable monsoons.

The cost is high: India has lost tens of billions of dollars to weather disasters in the last decade. The response needs a shift from structural flood control to living with water, which means:

• restoring wetlands and floodplains;
• sponge city design;
• nature-based solutions such as mangroves;
• heat-resilient urban planning;
• better last-mile warnings in local languages.

Odisha's cyclone model shows that sustained investment and community participation can save lives at scale.

Practice: additional question

*Why are heatwaves called a "silent disaster"? Suggest measures to protect vulnerable groups in Indian cities. (150 words)*

Tip for answers: pair every hazard with one Indian example, one institution (IMD, CWC, INCOIS or the NDMA) and one policy instrument. This shows both conceptual clarity and current awareness.