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.
Cold Air Masses – Cold, Dry Air Masses – Movement of air from Siberia/Canada into India.
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.
