Weather extremes and fire: heat and cold waves, lightning, dust storms and forest fires

Detail

1. Weather extremes as atmospheric hazards

• An atmospheric hazard is a danger that comes from the air and the weather. Examples are heat, cold, storms, lightning and dust.
• NCERT (Class 11, Table 6.1) lists the loo, cold waves, thunderstorms, dust storms and forest fires in this group.
• These hazards are seasonal. Most strike in the hot, dry pre-monsoon months (March-June) or in the winter months (December-February).

Hazard	Main season	Core region in India	Main trigger
Heat wave (loo)	April-June	Punjab, Haryana, Rajasthan, Madhya Pradesh; also central and east India	Hot, dry west winds; clear skies
Cold wave	December-February	Northwest India	Snowfall in nearby mountains; cold winds from the Caspian-Turkmenistan region
Thunderstorm and lightning	Pre-monsoon and monsoon	Bihar, Odisha, Jharkhand, West Bengal, Madhya Pradesh	Strong heating of the ground and rising moist air
Dust storm	April-June	Rajasthan, Punjab, Haryana, western Uttar Pradesh	Strong winds over dry, loose soil
Forest fire	February-June	Uttarakhand, Himachal Pradesh, Madhya Pradesh, Chhattisgarh, Western Ghats, Odisha, northeast	Mostly started by people; spread by dry weather and wind

2. Heat wave (the loo)

• Heat wave: a period of air temperature that is much hotter than normal for a place. In India it is judged only by the maximum (day) temperature [5].
• Loo: the hot, dry and dusty west winds that blow in the afternoons over Punjab, Haryana, Rajasthan and Madhya Pradesh in April-June.
• Why it happens in northwest India:
• The sun is almost overhead in May-June. The dry land heats up fast.
• Clear skies and no moisture mean there are no clouds to block the sun.
• Hot winds from the Thar Desert carry the heat east over the plains.

IMD criteria [5]

Basis	Heat wave	Severe heat wave
Starting condition	Maximum ≥ 40°C (plains), ≥ 37°C (coastal stations), ≥ 30°C (hills)	Same
Departure from normal	4.5°C to 6.4°C above normal	More than 6.4°C above normal (that is, 6.5°C or more)
Actual maximum (plains)	≥ 45°C	≥ 47°C

• Urban heat island (UHI): a city that is warmer than the countryside around it.
• Cause: concrete, asphalt and roofs soak up heat by day. Vehicles, ACs and factories add more heat, and there are few trees.
• Process: the stored heat is let out slowly at night, so the city does not cool down.
• Result: hot nights add to the day's heat. City dwellers, outdoor workers and slum dwellers suffer most.

3. Heat Action Plans (HAPs)

• Heat Action Plan: an early warning and preparedness plan for extreme heat. It sets out immediate and long-term actions to prepare, share information and coordinate the response, so that fewer vulnerable people fall ill or die [2].
• Ahmedabad (Gujarat) made South Asia's first HAP in 2013, after the deadly 2010 heat wave.
• NDMA heat-wave guidelines (2016, revised 2019) guide the plans made by states and cities.
• NDMA and the state governments jointly carry out HAPs in 23 heat-prone states [2][3]. NDMA and IMD work with these states to build the plans [3].
• A typical HAP has four parts:
• Early warning: colour-coded IMD alerts.
• Public awareness: drink water, avoid noon sun.
• Health-system readiness: cool wards, ORS stocks.

• Long-term steps: cool roofs, shade and green cover, and changing work hours.

• Legal status: heat is not a notified disaster under the national list used for relief funds.

4. Cold wave

• Cold wave: a spell of very low minimum (night) temperature compared with normal. It hits northwest India in December-February.
• Why it happens:
• Western disturbances (low-pressure storms that come from the Mediterranean region and move east) bring snowfall to the nearby Himalayas.
• Cold, dry winds then blow in from the Caspian Sea-Turkmenistan region and across the Himalayas into the northern plains.

• Clear, calm nights let the ground lose heat quickly. This brings frost (ice crystals on surfaces) and dense fog.

• Effects: deaths among the homeless and the old, frost damage to crops such as mustard and potato, and fog that disrupts rail, road and air traffic.

IMD criteria [6]

Basis	Cold wave	Severe cold wave
Starting condition	Minimum ≤ 10°C (plains), ≤ 0°C (hills)	Same
Departure from normal	−4.5°C to −6.4°C	−6.4°C or lower
Actual minimum (plains only)	≤ 4°C	≤ 2°C

• A cold wave is declared on the second day, once at least 2 stations in a meteorological sub-division meet the criteria for two days in a row [6].

5. Thunderstorms and lightning

• Thunderstorm: a local storm with heavy rain, strong gusts of wind, thunder and lightning. Hail may also fall.
• Cause: strong heating of the ground in the pre-monsoon months.
• Process: warm, moist air rises fast and forms tall cumulonimbus clouds (tall, dark, towering rain clouds). Ice and water particles collide inside the cloud and separate electric charges.

• Result: a sudden electric spark (lightning) jumps within the cloud or between the cloud and the ground.

• Regional names: in the pre-monsoon season these storms are called Kalbaisakhi ("calamity of the month of Baisakh") in West Bengal and Bardoli Chheerha in Assam.

• Lightning is one of India's biggest natural killers. The worst-hit states are Bihar, Odisha, Jharkhand, West Bengal and Madhya Pradesh. Strikes peak in the pre-monsoon and monsoon months.

• Victims are mostly farmers and labourers working in open fields, or people sheltering under trees.

• Early warning:

• Damini app: launched in 2020 by IITM-Pune (Indian Institute of Tropical Meteorology). It uses GPS to alert users to lightning within 20 km and 40 km of them and gives warnings valid for the next 40 minutes [9].
• The app warns in English and Hindi and has been downloaded more than 5 lakh times [9].
• IITM runs a lightning location network at 83 places across India. It locates strikes with less than 500 m accuracy [9].
• Through NDMA initiatives, lightning location alerts can be given about 6 minutes ahead for a spot, and a few hours ahead for a large area [4].
• NDMA reviews state preparedness for heat wave and lightning together before each summer [4].

6. Dust storms

• Dust storm: a strong wind that lifts loose, dry soil and carries it as a thick wall of dust.
• Cause: drought dries the topsoil, and there is little plant cover to hold it.
• Process: strong, hot surface winds (often the front of a thunderstorm) lift the fine particles high into the air.

• Result: visibility drops close to zero. Trees, poles and houses fall, crops and topsoil are lost, and air quality worsens.

• Where: deserts and semi-arid areas with sparse vegetation. In India this means Rajasthan, Punjab, Haryana and western Uttar Pradesh in April-June.

• Worldwide: the Sahara (Africa), the Arabian Peninsula, the Gobi (China and Mongolia) and the US Great Plains (the 1930s "Dust Bowl").
• Case: the May 2018 dust storms killed over a hundred people in Rajasthan and Uttar Pradesh.

7. Forest fires

• Forest fire: an uncontrolled fire in a forest. It is usually started by people and spread by dry weather and wind.
• Human causes: burning to clear land, careless use of fire, and jhum (shifting cultivation: slash-and-burn farming in the northeast).

• Natural factors: dry leaf litter, low humidity, high heat and wind help the fire spread.

• Season: February-June. Fires are worst in dry deciduous forests (trees that shed their leaves in the dry season) and chir-pine forests.

• Chir-pine needles are full of resin and burn easily. This is why Uttarakhand is so fire-prone.

• Places: Uttarakhand, Himachal Pradesh, Madhya Pradesh, Chhattisgarh, the Western Ghats, Odisha and the northeast.

• Major cases: Uttarakhand 2016 and 2024.
• Damage: forests and wildlife are lost, the air is polluted with smoke and carbon, the soil is exposed to erosion, and forest-dependent communities are displaced.

Satellite alerts by FSI (Forest Survey of India) [7]

• FSI alerts State Forest Departments to fires picked up by:
• MODIS sensors on NASA's Aqua and Terra satellites, at 1 km × 1 km resolution;

• the SNPP-VIIRS sensor, at 375 m × 375 m resolution.

• Alerts go out at least six times in 24 hours.

• The fire hotspots (small areas of very high heat seen from a satellite) are received at the Shadnagar Earth Station of NRSC (Telangana) and processed there.
• Alerts are sent by email with Google Earth KML files to the head of each state's forest force and to the fire nodal officers. Registered users can get SMS alerts down to beat level (the smallest forest patrol unit).

National Action Plan on Forest Fires (NAPFF, 2018) [8]

• The Environment Ministry made the plan after recommendations of a Parliamentary Committee and directions of the NGT (National Green Tribunal).
• It is based on a study with the World Bank and on consultations with State Forest Departments and NDMA.
• Aim: to reduce forest fires by informing, enabling and empowering forest-fringe communities (people living at the edge of forests) [8].

Prelims Hooks

• Loo: hot, dry west wind over Punjab, Haryana, Rajasthan and Madhya Pradesh in April-June. It is not a monsoon or winter wind.
• IMD heat-wave thresholds: plains ≥ 40°C, coasts ≥ 37°C, hills ≥ 30°C. A maximum of 45°C is a heat wave and 47°C is a severe heat wave [5].
• Trap: heat waves are defined only by the maximum temperature, and cold waves by the minimum temperature [5][6].
• Cold-wave thresholds: plains ≤ 10°C, hills ≤ 0°C. In the plains, an actual minimum ≤ 4°C is a cold wave and ≤ 2°C is a severe cold wave [6].
• First Heat Action Plan in South Asia: Ahmedabad, 2013, after the 2010 heat wave.
• Damini app: made by IITM-Pune (not IMD or ISRO). It launched in 2020 and alerts users to lightning within 20-40 km [9].
• FSI fire alerts: MODIS at 1 km and SNPP-VIIRS at 375 m. Data is received at Shadnagar (NRSC) [7].
• Chir pine and dry deciduous forests are the most fire-prone. Fire season: February-June.
• Dust storm belt: Rajasthan, Punjab, Haryana and western Uttar Pradesh, in April-June.

Mains Points

• Heat is a growing "silent disaster":
• Urban heat islands, outdoor informal work and the lack of a notified-disaster status hold back the response.
• Plans like Ahmedabad's show that early warning, cooler shelters and changed work hours save lives.

• Wider rollout through NDMA's 23-state Heat Action Plan network is the policy answer [2][3].

• Lightning kills many but gets little attention:

• Deaths are concentrated among the rural poor in Bihar, Odisha, Jharkhand, West Bengal and Madhya Pradesh.

• Fixes include last-mile alerts (Damini, the 83-station network), lightning arresters on schools and public buildings, and community awareness [4][9].

• Forest fires are a human-made hazard made worse by weather:

• Jhum burning, flammable chir-pine litter and hotter, drier pre-monsoon months all add to the risk.
• Responses include satellite alerts (FSI), community-based prevention (NAPFF 2018), fire lines and controlled burning [7][8].

• These link to Sendai Framework priorities on understanding risk and on early warning.

• Dust storms and cold waves: they show how land degradation (bare, dry soil) and regional weather (western disturbances, Caspian winds) turn routine seasons into disasters. Fixes include shelterbelts (rows of trees planted to break the wind), better soil cover and impact-based forecasts.