Air pollution levels are likely to spike and ‘cold wave’ to ‘severe cold wave’ conditions are likely to set in over many parts of northwest India, including Delhi, from December 29, the India Meteorological Department has said.
Delhi recorded an air quality index (AQI) of 337 in the “very poor” category on Saturday.
Under the influence of an approaching western disturbance, widespread snowfall is very likely over Jammu, Kashmir, Ladakh, Gilgit, Baltistan and Muzaffarabad; scattered snowfall is likely over Himachal Pradesh, Uttarakhand; and light rain or thundershowers is likely over northern parts of Punjab, Haryana and Chandigarh on December 27 and 28, the IMD said.
After the western disturbance moves away and under the influence of the consequent strengthening of cold and dry north-westerly or northerly lower level winds, “cold wave” to “severe cold wave” conditions are likely to re-establish over Punjab, Haryana, Chandigarh, Delhi, Rajasthan and West Uttar Pradesh from December 29.
“The impact of the western disturbance will be mainly in Jammu and Kashmir and Himachal Pradesh where moderate rain or snowfall is expected. In Delhi, we can expect clouding and trace rainfall. After the WD passes, cold wave is likely to be established for three to four days from December 29 onwards. We already have very low minimum temperatures bordering cold wave conditions,” said Kuldeep Shrivastava, head, regional weather forecasting centre.
Northern parts of Saurashtra, Kutch and west Madhya Pradesh are also likely to experience cold wave conditions. Ground frost conditions are likely in isolated pockets over Uttarakhand, Himachal Pradesh, Punjab, Haryana, Chandigarh, Delhi, Rajasthan and west Madhya Pradesh between December 28 and 29.
‘Cold day’ conditions are also likely over Punjab, Haryana, Chandigarh and Delhi on December 28 and 29 and over North Rajasthan December 29 and 30. Dense to very dense fog is likely over Punjab, Haryana, Chandigarh, Delhi on December 28, 29 and 30.
According to IMD, a ‘cold day’ or ‘severe cold day’ is considered when the minimum temperature is under 10 degrees and the maximum temperature is 4.5 degree C or 6.4 degree C below normal. A cold wave occurs in plains when the minimum temperature is 10 degrees Celsius or below, and is 4.5 notches lesser than the season’s normal for two consecutive days.
On December 27, when the wind direction changes temporarily to easterly, wind speed is likely to reduce leading to a spike in pollution levels. “We always see that during the transition of winds, air pollution levels go up but after that wind speed is likely to pick up,” said Shrivastava.
According to air quality early warning system under the ministry of earth sciences, ventilation index on Sunday is likely to be 3500 m2/s. The ventilation index is a function of the mixing height and the wind speed and defines the ability of the atmosphere to disperse contaminants. A ventilation index below 2,350 m2/s is considered poor. Mixing height is the height at which pollutants mix in the air.