Cold Waves: A Natural Hazard

🧭 Definition

A cold wave is a marked drop in temperature over a large area, caused by the advection (horizontal movement) of very cold air masses from higher latitudes into lower latitudes.
It is often accompanied by frost, fog, or strong winds — leading to physiological stress, crop damage, and sometimes death.

According to IMD:

• Cold Wave: When minimum temperature is 4.5°C–6.4°C below normal.
• Severe Cold Wave: When minimum temperature is
  • >6.4°C below normal, or
  • ≤ 4°C in plains, or
  • ≤ 0°C in hilly areas.

🌀 Mechanism / Causes of Cold Waves

Causative Factor	Explanation
1️⃣ Transport of Cold Air	Cold continental air from higher latitudes moves southwards into India, especially during winter months.
2️⃣ Western Disturbances (Jet Stream Influence)	These are eastward-moving westerly troughs in the upper troposphere north of 20°N, bringing cold dry air from Central Asia.
3️⃣ La Niña Phase	Strengthens easterlies, allowing cold Siberian air to penetrate further south.
4️⃣ Radiational Cooling	Clear skies and calm winds at night enhance terrestrial radiation loss → sharp fall in surface temperature.
5️⃣ Low Pressure over Arabian Sea	In rare cases, easterlies north of such systems transport cold air into NW India.

🌍 Spatial Distribution Pattern in India

Region	Characteristics / Impact
Northern India (Punjab, Haryana, Rajasthan, UP, Bihar)	Most affected. Minimum temperature often drops below freezing. Cold waves peak in Dec–Jan.
Indo-Gangetic Plains	Experience combined effect of cold wave + fog.
Central India (MP, Chhattisgarh)	Occasionally affected when cold winds penetrate southward.
Peninsular India	Rarely experiences cold waves due to maritime moderation and proximity to the equator.
Himalayan States	Cold conditions normal, but frostbite and hypothermia common.

Why extreme cold in North India?

1️⃣ Continental location (far from sea).
2️⃣ Snowfall in Himalayas → cold air descends to plains.
3️⃣ Influx of cold winds from Caspian Sea and Turkmenistan via NW passes (Feb peak).

🩺 Associated Health Hazards

Term	Meaning
Wind Chill	Perceived temperature due to combined effect of wind & cold. Wind removes body heat faster than calm air.
Frostbite	Freezing and tissue damage of exposed body parts (fingers, toes, ears).
Hypothermia	Body temperature drops below 35°C (95°F) → risk of death if untreated.

🚜 Cold Wave Hazard Mitigation (NDMA-aligned Actions)

Sector	Measures
Agriculture	– Follow District Crop Contingency Plans. – Provide light irrigation to reduce frost formation. – Prune frost-damaged plant parts. – Burn leaves/waste to create smoke & reduce radiation loss. – Use foliar fertilizer sprays and resistant varieties.
Public Health & Shelter	– Convert schools/public halls into shelters for vulnerable groups. – Ensure blankets, heating arrangements, & hot food. – Special outreach for elderly, children, and sick persons.
Infrastructure & Utilities	– Insulate water pipes and critical installations to prevent freezing. – Maintain power supply for heating and water pumping.
Community Preparedness	– Promote awareness through SHGs, PRIs, and NGOs. – Encourage early warning use from IMD bulletins. – Train volunteers for first aid in frostbite/hypothermia.

🧩 Existing Challenges

1️⃣ Localised nature — No uniform national plan; mitigation must be state/district-specific.
2️⃣ Low community participation — Weak coordination with PRIs, SHGs.
3️⃣ Lack of anticipatory preparedness — Reactive rather than preventive action.
4️⃣ Data gap on cold-related deaths — Underreporting and poor record-keeping.
5️⃣ Urban exposure — Homeless populations and inadequate shelter planning in cities.

🧠 Conceptual Contrast: Heat Wave vs. Cold Wave

Aspect	Heat Wave	Cold Wave
Season	Apr–Jun	Nov–Feb
Pressure System	High pressure ridge (subsiding warm air)	High pressure ridge (descending cold air)
Dominant Winds	Hot, dry continental	Cold, dry continental
Health Impact	Heat stroke, dehydration	Hypothermia, frostbite
Affected Region	NW, Central, E. India	N, NW, Indo-Gangetic
Mitigation	Cool roofs, green cover, early warning	Shelter, smoke irrigation, insulation
NDMA Priority	National HAPs (city-based)	Localised frost management plans

📚 Cold Wave Criteria — IMD “Mercurial Meter”

Basis	Condition	Category
Departure from Normal Minimum Temp	4.5°C – 6.4°C below normal	Cold Wave
	>6.4°C below normal	Severe Cold Wave
Actual Minimum Temp (Plains)	≤ 4°C	Cold Wave
	≤ 0°C	Severe Cold Wave
Actual Minimum Temp (Hills)	≤ 0°C	Cold Wave
	≤ –4°C	Severe Cold Wave