Source: TH
Subject: Geography
Context: A cold wave has gripped parts of Telangana, with districts like Kohir and Yalal recording temperatures near 8°C—3–5°C below normal.
About Cold Wave:
What is a Cold Wave?
- A cold wave refers to a sharp and unusual drop in minimum temperatures, severe enough to cause physiological stress or danger to humans. It is declared when temperatures fall below defined IMD thresholds in plains or hilly regions.
IMD Criteria for Cold Wave:
- Plains:
- Minimum temperature ≤10°C and 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 less.
- Coastal regions: Cold wave when departure ≤ –4.5°C and minimum temperature ≤15°C.
- Must be observed in at least two stations for two consecutive days.
How a Cold Wave Occurs (Mechanism)?
- Cold waves originate when high-pressure systems over North/Northwest India push cold, dry continental winds
- Clear skies and low moisture allow rapid radiational cooling at night, dropping temperatures sharply over inland regions like the Deccan plateau.
Key Features of Cold Waves:
- Sharp fall in minimum temperatures at night despite warm days (28–31°C in Telangana).
- Enhanced cooling over rural/open landscapes and elevated plateaus.
- Urban areas like Hyderabad experience milder cooling due to urban heat island effect.
- Occur mainly in post-monsoon and winter months (Nov–Feb).
Implications of Cold Waves:
- Increases risk of hypothermia and frostbite among the vulnerable (elderly, homeless, infants).
- Exacerbates pulmonary diseases such as asthma, COPD, and bronchitis due to dry air.
- Surge in common respiratory infections (flu, pneumonia).
- Impacts agriculture through cold stress on crops in northern districts.
