Cold Wave in Northwest India

Subject – Geography

Context – IMD has predicted a cold wave in Northwest India

Concept –

The India Meteorological Department (IMD) has predicted a cold wave in parts of Punjab, Haryana, Chandigarh, Gujarat, Rajasthan and Uttar Pradesh over the next few days.
A western disturbance as a cyclonic circulation lies over north Pakistan and adjoining Jammu and Kashmir, according to an IMD bulletin.
Western disturbances are storms that originate in the Mediterranean region and bring winter rainfall to northwest India.
In this gap of five to six days, the IMD expects strong north-westerly and westerly cold winds over north India.
The minimum temperature is likely to fall by 2 to 4 degree Celsius in these places over the next few days, going by the forecast.

What is a cold wave?

The IMD records a cold wave when the minimum temperature is equal to or less than 10 degree Celsius at a weather station in the plains, and is 4.5 degrees to 6.4 degrees below the normal temperature for that period.
A cold wave may also be recorded at a station in the plains when the minimum temperature is less than or equal to 4 degree Celsius.
For hilly regions, a cold wave is declared when the minimum temperature is less than or equal to 0 degree Celsius and the minimum temperature is 4.5 degrees to 6.4 degrees below the normal.
The ‘normal’ temperature is calculated for every five days by taking the average temperature for these days over the past 30 years.
The IMD defines a cold wave qualitatively as “a condition of air temperature which becomes fatal to the human body when exposed.”
The IMD also has an ‘impact matrix’ for cold waves – when cold wave conditions persist in isolated areas for more than two days, the impact matrix indicates that the cold is tolerable but “a mild health concern for vulnerable people (infants, pregnant women, elderly, people with chronic diseases etc.
In ‘severe’ cold wave conditions, where the minimum temperature is less than or equal to 10 degree Celsius, and departs from the normal by 6.5 degrees or more, or if cold wave conditions persist for four days or more, the IMD’s impact matrix indicates an increased likelihood of illnesses like flu, due to prolonged exposure to the cold.

Why do cold waves occur?

Cold waves usually occur from mid-December to the end of February.
The cold waves depend on weather systems and wind patterns from the middle latitudes, that is from Europe or West Asia, since the winds from these regions bring cold weather.
According to the IMD, the factors that bring cold waves to India include the movement of cold air masses brought about by upper-level winds. They can be triggered by strong westerly winds approaching northwest India and transporting cold air towards the southeast direction.
Build-up of an extended area of relatively high pressure over northwest Asia can also bring cold waves.