Heat Wave and Cold Wave: Quick Answer
IMD considers a heat wave only when a station's maximum temperature reaches at least 40°C in the plains, 37°C on the coast or 30°C in the hills. It is then declared when the maximum is 4.5°C to 6.4°C above normal (heat wave) or more than 6.4°C above normal (severe heat wave), or when the actual maximum is 45°C or more (heat wave) or 47°C or more (severe heat wave). A cold wave is considered when the minimum temperature falls to 10°C or less in the plains or 0°C or less in the hills, and is declared at 4.5°C to 6.4°C below normal, or an actual minimum of 4°C or less in the plains (severe: 2°C or less). In both cases the criteria must be met at at least 2 stations in a meteorological sub-division for 2 consecutive days, and the wave is declared on the second day (IMD FAQs on Heat Wave and Cold Wave).
Key exam takeaway: heat waves in India occur mainly March to June with May as the peak month; cold waves are linked to the cold north-westerly winds of December–February, and a passing western disturbance temporarily eases them.
As of November 2026 these are the criteria IMD publishes on its heat and cold wave pages. Background: Indian Climate Notes for SSC.
Heat Wave Criteria (IMD)
| Condition | Heat wave | Severe heat wave |
|---|---|---|
| Minimum threshold to be considered | Max ≥ 40°C (plains), ≥ 30°C (hills) | Same |
| Based on departure from normal | +4.5°C to +6.4°C | More than +6.4°C |
| Based on actual maximum (plains) | ≥ 45°C | ≥ 47°C |
| Coastal stations | Departure ≥ +4.5°C, provided actual max ≥ 37°C | — |
| Duration rule | 2 stations in a sub-division, 2 consecutive days; declared on day 2 | Same |
Warm night: declared only when the maximum stays at 40°C or more; minimum temperature 4.5°C to 6.4°C above normal (very warm night: more than 6.4°C). Hot and humid weather: maximum 3°C above normal with above-normal humidity.
Cold Wave Criteria (IMD)
| Condition | Cold wave | Severe cold wave |
|---|---|---|
| Minimum threshold to be considered | Min ≤ 10°C (plains), ≤ 0°C (hills) | Same |
| Based on departure from normal | −4.5°C to −6.4°C | −6.4°C or less |
| Based on actual minimum (plains only) | ≤ 4°C | ≤ 2°C |
| Coastal stations | Departure ≤ −4.5°C, provided actual min ≤ 15°C | — |
| Duration rule | 2 stations in a sub-division, 2 consecutive days; declared on day 2 | Same |
Cold day: when the minimum is 10°C or less (plains) or 0°C or less (hills) and the maximum temperature is 4.5°C to 6.4°C below normal (severe cold day: more than 6.4°C below). Cold days happen when persistent low cloud or fog blocks sunshine over the north Indian plains.
Heat Wave vs Cold Wave: Comparison
| Point | Heat wave | Cold wave |
|---|---|---|
| Temperature measured | Maximum (day) | Minimum (night); cold day uses maximum |
| Season | March–June, rarely July; peak May | December–February; December and January coldest in north India |
| Prone areas (IMD) | Plains of north-west, central, east and north peninsular India: Punjab, Haryana, Delhi, UP, Bihar, Jharkhand, West Bengal, Odisha, MP, Chhattisgarh, Rajasthan, Gujarat, parts of Maharashtra and Karnataka, Andhra Pradesh, Telangana; sometimes Tamil Nadu and Kerala | Plains of north-west and adjoining central India have the most cold-wave days (6–8 a year on average); also Sikkim, Assam, Bihar, West Bengal, Odisha and others |
| Favourable conditions | Hot dry air, no upper-level moisture, cloudless sky, large anticyclonic flow | Cold north-westerly winds from Central Asia / Hindukush over the Indo-Gangetic plains |
| Effect of a western disturbance | — | Clouds and moist winds raise the minimum and ease the cold wave; after it passes, clear skies bring it back |
See western disturbances in India for how winter systems change night temperatures.
Colour-Coded Alerts (IMD with NDMA)
| Colour | Meaning | Heat example | Cold example |
|---|---|---|---|
| Green | No action | Max near normal | Min near normal |
| Yellow | Be updated | Heat wave in isolated pockets for 2 days | Cold wave in isolated areas for 2 days |
| Orange | Be prepared | Severe heat wave for 2 days, or heat wave for 4+ days | Severe cold wave for 2 days, or cold wave for 4+ days |
| Red | Take action | Severe heat wave for more than 2 days, or more than 6 heat-wave days | Severe cold wave for more than 2 days, or more than 6 cold-wave days |
Local Hot and Cold Weather Words (NCERT)
- Loo: hot, dry, oppressive winds over the northern plains from Punjab to Bihar, strongest between Delhi and Patna, in May–June.
- Cold wave and frost: around February, cold winds from the Caspian Sea and Turkmenistan bring cold wave, frost and fog to north-western India.
- Extremes: Churu (Rajasthan) can record 50°C or more on a June day; Drass (Ladakh) can drop to −45°C on a December night.
Heat Wave and Cold Wave: 10 Practice MCQs
Q1. For a plains station, IMD considers a heat wave only if the maximum temperature reaches at least: (a) 35°C (b) 37°C (c) 40°C (d) 45°C Answer: (c).
Q2. A severe heat wave based on actual maximum temperature in the plains is declared at: (a) ≥ 42°C (b) ≥ 45°C (c) ≥ 47°C (d) ≥ 50°C Answer: (c).
Q3. The peak month of heat waves in India is: (a) March (b) April (c) May (d) July Answer: (c). IMD FAQ.
Q4. For coastal stations, a heat wave may be described if the actual maximum is at least: (a) 30°C (b) 35°C (c) 37°C (d) 40°C Answer: (c).
Q5. A cold wave in the plains based on actual minimum temperature is declared at: (a) ≤ 10°C (b) ≤ 6°C (c) ≤ 4°C (d) ≤ 0°C Answer: (c). Severe cold wave: ≤ 2°C.
Q6. A "cold day" is defined using the departure of the: (a) Minimum temperature (b) Maximum temperature (c) Dew point (d) Wind speed Answer: (b).
Q7. How many stations in a sub-division must meet the criteria to declare a heat or cold wave? (a) 1 (b) 2 (c) 3 (d) 5 Answer: (b). For 2 consecutive days, declared on the second day.
Q8. Hot, dry winds called "Loo" blow most strongly between: (a) Mumbai and Pune (b) Delhi and Patna (c) Kolkata and Guwahati (d) Chennai and Bengaluru Answer: (b). NCERT.
Q9. The arrival of a western disturbance over north India in winter usually: (a) Intensifies the cold wave (b) Eases the cold wave by raising minimum temperatures (c) Causes a heat wave (d) Has no effect Answer: (b). IMD cold wave FAQ.
Q10. An orange heat alert is issued when: (a) Max is near normal (b) Heat wave in isolated pockets for 2 days (c) Severe heat wave persists for 2 days (d) Heat wave for 1 day Answer: (c). Or heat wave for 4 days or more.
More practice: Indian climate MCQs for SSC, SSC CGL geography mock test 01.
Heat Wave and Cold Wave FAQs
What is the IMD criterion for a heat wave?
A maximum of at least 40°C (plains), 37°C (coast) or 30°C (hills), plus a departure of 4.5°C to 6.4°C above normal, or an actual maximum of 45°C or more in the plains.
What is the difference between a heat wave and a severe heat wave?
A severe heat wave is more than 6.4°C above normal, or an actual maximum of 47°C or more in the plains.
What is the IMD criterion for a cold wave?
A minimum of 10°C or less (plains) or 0°C or less (hills), with a departure of 4.5°C to 6.4°C below normal, or an actual minimum of 4°C or less in the plains.
Which months have heat waves in India?
Mainly March to June, rarely July; May is the peak month, as per IMD.
What is the difference between a cold wave and a cold day?
A cold wave is judged on the minimum (night) temperature; a cold day is judged on how far the maximum (day) temperature falls below normal, usually under fog or low cloud.
Practice Next for Indian Geography
- Related: Monsoon onset and withdrawal, Drought and floods in India, Cyclones in India
- Also read: Rainfall distribution in India
Sources: IMD, FAQ on Heat Wave; IMD, FAQ on Cold Wave; NCERT Class 11, India: Physical Environment, Chapter 4. Last checked 7 November 2026.