Syllabus: Salient features of world’s physical geography.
What is a Cold Wave?
- A cold wave is a significant and unusual fall in minimum temperatures that can cause physiological stress or danger to humans.
- It is formally declared when the minimum temperature meets the IMD’s defined thresholds for plains, hilly areas, or coastal belts.
IMD Criteria for Cold Wave
- For Plains
- Minimum temperature ≤10°C with departure –4.5°C to –6.4°C → Cold Wave.
- Departure ≤ –6.4°C → Severe Cold Wave.
- Independent of normal:
- ≤4°C → Cold Wave
- ≤2°C → Severe Cold Wave
- Hilly Regions
- Minimum temperature 0°C or below.
- Coastal Regions
- Minimum temperature ≤15°C and departure ≤ –4.5°C.
- General Rule
- Must be recorded in at least two stations for two consecutive days.
How Cold Waves Develop (Mechanism)
- A strong high-pressure system over North or Northwest India drives cold, dry continental winds southwards.
- Clear skies and low humidity promote rapid radiational cooling at night, especially over open, rural and elevated areas like the Deccan plateau.
- Urban centres show milder drops due to the urban heat island effect.
Features
- Sharp fall in night temperatures despite warm daytime highs (28–31°C in Telangana).
- Strong cooling over plateaus, rural belts, and inland regions.
- Occur mainly during November–February.
Impacts
- Increased risk of hypothermia, frostbite, and weather-related stress in vulnerable groups.
- Aggravates asthma, COPD, bronchitis due to cold and dry air.
- Higher incidence of flu and respiratory infections.
- Causes cold stress on crops, affecting agriculture in northern districts.
