Coldest October in 58 years, but numerous farm fires keep Delhi air in ICU

Kuldeep Srivastava, head of IMD’s Regional Weather Forecasting Centre, confirmed that this year, minimum temperatures in Delhi have been lower than normal.

This October was the coldest Delhi has experienced in 58 years, with the mean minimum temperature for the month settling at 17.2 degrees Celsius, the India Meteorological Department (IMD) said. The last time it was this cold at night in the national capital was in 1962, when the mean minimum temperature for October was 16.9 degrees Celsius, weather experts said.

Normally, Delhi records a mean minimum temperature -- the average of daily minimum temperatures through the month --of 19.1 degrees Celsius in October.

Kuldeep Srivastava, head of IMD’s Regional Weather Forecasting Centre, confirmed that this year, minimum temperatures in Delhi have been lower than normal.

“The absence of cloud cover is a major reason for such low minimum temperatures. Clouds trap some of the outgoing infrared radiation and radiate it back downwards, warming the ground. Another reason is calm winds, which allow the formation of mist and fog,” Srivastava said.

On Saturday, the maximum temperature at the Safdarjung observatory -- considered the official reading for the city -- was 30.8 degrees Celsius. The minimum temperature was 13 degrees Celsius, three degrees below the season’s normal

But despite high wind speed and favourable weather conditions, the national capital’s air quality continued to remain in the ‘very poor’ category on the air quality index (AQI). The AQI, as recorded by the Central Pollution Control Board (CPCB), on Saturday was 367 (very poor). This was only slightly better than the AQI of 374 on Friday, also in ‘very poor’ category. On a scale of 0 to 500, an AQI between 301 and 400 is considered very poor.

IMD scientists said while the average wind speed during Saturday had touched 18kmph, it did not clean up the air as expected.

VK Soni, head of IMD’s Environment Monitoring Research Centre, said looking at the high wind speed during the day, the forecast was that the AQI would improve and reach the ‘poor’ category (between 201 and 300). On Friday and Saturday, the number of stubble burning incidents spotted in the neighbouring states of Punjab and Haryana was the highest this season so far, which could have contributed to the air continuing to remain critical.

“As per IMD’s satellite monitoring on Friday, in Punjab alone there were 4,266 farm fire spots, while in Haryana there were 155 farm fires. On Saturday, too, the number of red dots, denoting fires, were over 3,000. Even though we had good wind speed and better ventilation index, the direction of the wind was from north-west, which brought with it smoke from the fires,” Soni said.

He said the wind speed is expected to remain high on Sunday, which will keep the AQI levels in the upper ends of the ‘very poor’ zone.

Union ministry’s System of Air Quality and Weather Forecasting and Research (Safar) data showed that 3,471 farm fires were spotted over Punjab and Haryana, which accounted for 32% of Delhi’s PM2.5 (particulate matter with diameters less than 2.5 micrometres) levels.