Severe cold days may be linked to air pollution, say scientists

The minimum temperature at Safdarjung observatory was only 2.4 degree C, 5 degrees below normal; 1.7 degree C at Lodhi road; 1.9 degree C at Ayanagar and 3.1 degree C at Palam.
Women and children warm themselves around a bonfire at Safdarjung in New Delhi.(Sanchit Khanna/HT PHOTO)
Women and children warm themselves around a bonfire at Safdarjung in New Delhi.(Sanchit Khanna/HT PHOTO)
Updated on Dec 28, 2019 10:36 PM IST
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Hindustan Times, New Delhi | ByJayashree Nandi

Delhi recorded a severe cold day on Saturday along with severe cold wave conditions increasing the intensity of cold a notch higher than what was felt in the rest of December. Delhi has been experiencing a cold spell for 15 days now.

The minimum temperature at Safdarjung observatory was only 2.4 degree C, 5 degrees below normal; 1.7 degree C at Lodhi road; 1.9 degree C at Ayanagar and 3.1 degree C at Palam. The minimum at Safdarjung is the coldest since December 11, 1996 when the minimum was 2.3 degree C and same as December 30, 2013 when the minimum was 2.4 degree C. The all time record for Delhi is 0.0 degree C recorded on December 27, 1930. When the minimum temperature is 2 degrees it meets the “severe cold wave” criteria according to IMD.

The maximum temperature at Safdarjung was 13.3 degree C, 7 degrees below normal; only 11.2 at Palam and 11.6 at Ayanagar meeting the “severe cold day” criteria. These conditions will persist in Delhi till December 31 after which a western disturbance is likely to bring thundershowers in many parts of Delhi and NCR.

Not only Delhi similarly severe cold conditions affected most parts of northwest India on Saturday. The minimum temperature at Mt Abu for example was -1.5 degree C, 5 degrees below normal; Churu was 1.1 degree C, 4 degrees below normal; Hisar at 0.2 degree C, 7 degrees below normal; Bareily at 3.3 degree C, 5 degrees below normal; Bahraich at 2 degrees, 7 degrees below normal; Kanpur at 2, 6 degrees below normal are a few examples. Maximum temperatures in many parts of northern India similarly ranged between 8 to 11 degree C which is 8 to 10 degrees below normal. Most affected regions include Bahraich, Gorakhpur, Varanasi, Meerut, Bareily, Hisar, Chandigarh, Ambala and others.

‘“Severe cold wave and severe cold day conditions prevailed at many to most pockets over Punjab, Haryana, Chandigarh & Delhi, Uttar Pradesh and Bihar and in isolated pockets over Rajasthan,” IMD’s bulletin for Saturday said.

“ Due to persistence of cold northwesterly winds in lower levels over northwest India and other favourable meteorological conditions Cold wave to severe cold wave conditions along with Cold day to severe cold day conditions in many to most pockets very likely over Punjab, Haryana, Chandigarh & Delhi, north Rajasthan and West Uttar Pradesh during next 2 days. Cold wave to severe cold wave along with cold day to severe cold day conditions is also very likely at a few pockets over East Uttar Pradesh & Bihar during next 2 days,” IMD has forecast.

Very dense fog in Delhi reduced visibility at Palam to 0 meters and only 100 meters at Safdarjung in the morning hours. The mean maximum temperature for December till now is 19.18 degree C making it almost certain that this December will the second coldest in a century. The lowest mean maximum for December was recorded in 1997 at 17.3 degree C.

“Severe cold wave and cold day conditions will continue for two more days. The minimum temperature on Sunday may drop further. We are expecting a marginal rise in temperature on December 31 and 1 and rains from December 31 night which is likely to relieve severe cold day conditions,” said Kuldeep Shrivastava, head of Regional Weather Forecasting Centre.

Are low day temperatures linked to air pollution in the northwestern region?

Meteorologists have been noticing the phenomenon of extremely low day temperatures or cold spells accompanied by dense fog or low cloud cover over NW India more often since 1997.

“In 1976 there was a cold spell for six days. But after that the phenomenon has become more common in the late 90’s. If fog or low cloud hours increase obviously less solar energy is received and hence days are cold,” said RK Jenamani, senior scientist at National Weather Forecasting Centre.

Jenamani published a study in the Current Science journal in 2007 which said that there has been a fall in average maximum temperature by 2–3 degree C over 2 stations in the peak winter of January since 1989 with increase in average fog (all intensities of fog) hours per day by 8 h during the same period. “Correlation coefficients computed between various fog and no-fog hours with temperatures and pollutions also confirm that maximum temperatures over Delhi are strongly negatively correlated with fog hours which are strongly positively correlated with pollutant levels,” the study concludes. This essentially means that air pollution accentuates fog which in turn plays a role in reducing day temperatures. “The peak fog seasons were seen in the 1996 to 2007 period. Moisture and air pollution are highly linked. The life period of suspension of air pollutants is prolonged when there is moisture in the air. Low clouds which we are seeing over a very large area and very long period is nothing but fog at slightly higher level from the surface,” said Jenamani.

“When moisture is high pollution also goes up because particles become heavy and do aid in formation of fog or low clouds. But this needs to be studied further. There is a climate change link also, it makes various weather phenomenon more extreme. For example the previous western disturbance on December 12 and 13 was so strong that it brought a lot of rain in December and caused moisture incursion helping create a severe cold spell,” Shrivastava said.

“In the past few days we have seen low clouds descend to surface and cause dense fog and then rise up again in a few hours. Availability of moisture and low temperatures combined to create the low cloud cover. I don’t think there is a link with air pollution,” said Sachin Ghude, senior scientist at Indian Institute of Tropical Meteorology.

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