Why in News?
Recently, The India Meteorological Department (IMD) has issued a cold wave alert for four districts of Telangana.
What is a cold wave?
- Definition – According to world meteorological organization, cold wave is a period of marked and unusual cold weather characterised by a sharp and significant drop in air temperatures near the surface (maximum, minimum and daily average) over a large area and persisting below certain thresholds for at least two consecutive days during the cold season.
- Criteria of IMD (Indian Meteorological department)
- Cold Wave – Min temp ≤ 10°C (plains) AND ≥ 4.5°C below normal.
- Severe Cold Wave – Min temp ≤ 4°C (plains) OR ≥ 6.4°C below normal.
- Season of Occurrence – In India it primarily occurs between November to March, with December and January being the coldest months.
- Vulnerable regions – It hits the states of North & Central India such as: Punjab, Haryana, Delhi, Rajasthan, UP, MP, Chhattisgarh, Bihar, Jharkhand, West Bengal.
- Himalayan Regions – Naturally colder, criteria focus on deviation from normal.
- Causes
- Western Disturbances – Transient weather systems bringing moisture and cold air.
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- Cold Air Masses – Cold, Dry Air Masses – Movement of air from Siberia/Canada into India.
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- Snowfall – Heavy snow in the Himalayas triggers cold winds.
- Clear Skies – Lack of cloud cover allows heat to escape rapidly.
- Impacts
- Health – Hypothermia, frostbite, respiratory issues, increased mortality (infants, elderly).
- Agriculture – Damage to Rabi crops (wheat, coffee, tea).
- Energy – Spike in demand for heating fuels/electricity.
- Transport – Reduced visibility, accidents.
- Management
- Warnings and guidelines – Issued by IMD & NDMA (National disaster management authority)
- Preparedness – Emergency shelters, public awareness, heat retention tips (dry clothes, hot fluids).
- Agriculture – Shielding crops, animal care.
Why there is a persistent cold wave over Telangana recently?
- Combination of factors – Over Telangana right now, the India Meteorological Department (IMD) has pointed to a combination familiar in winter:
- Dry air,
- Clear skies,
- Continental winds.
- Unusual dry air mass - The air mass over Telangana State has been unusually dry of late.
- When humidity is low, the atmosphere holds less water vapour, which is one of the main greenhouse gases near the surface.
- With less water vapour to trap heat, the ground loses energy more efficiently after sunset.
- Clear skies strengthen this effect because clouds that might otherwise absorb and re-radiate some of the outgoing heat are absent.
- Meteorologists have already said the ongoing cold wave is partly linked to dry winds blowing north and northeast and clear skies at night.
- Influence of surface winds – The northerly and northeasterly surface winds bring cooler, drier air from inland parts of India rather than air from the Bay of Bengal, which is more moist.
- This steady cooling keeps the daily minimum temperature down even when the daytime temperature is ‘ordinary’ since each night begins with a cooler starting point.
- Telangana had a cold wave warning in mid-November but it has seemed to go on because these low-level winds haven’t shifted, thus the local air mass has remained cool and dry.
- Impact of weak disturbance – A weak western disturbance is expected to influence the western Himalaya the IMD has said there could be a 2-4ºC rise in the minimum temperature as the larger pattern evolves with the lower-level easterlies.
What lies ahead?
- In a press release issued by the IMD it has been said that cold-wave conditions had occurred at isolated places over Telangana and warned that such conditions were “very likely” over the State, as well as in north interior Karnataka.
- The bulletin also said there would be “no significant change” in minimum temperatures over “remaining parts of the country” during the next week.
- That is, the cold patterns won’t break in a sudden way.
Reference
The Hindu| Cold Waves
