Delhi’s air quality improved sharply on Friday after the Capital received its highest single-day October rainfall in four years, with the average Air Quality Index (AQI) falling from 222 in the poor category to 90 in the satisfactory category within a day, according to the Central Pollution Control Board.
The Safdarjung observatory recorded 61.4 mm of rain in the 24 hours ending 8.30 am on Friday. The rainfall was the highest recorded there for a single October day since October 9, 2022, when the station received 74 mm.
The showers were widespread across the city. India Meteorological Department data showed 63.4 mm of rain at Lodhi Road, 55.4 mm at Ayanagar, 53.5 mm at Chhatarpur, 50.3 mm at the Ridge and 43.1 mm at Palam. Jharoda Kalan recorded the highest rainfall among the stations, at 89 mm, as of Friday morning.
The rain also pushed Delhi’s October rainfall total well above the monthly normal. Safdarjung had recorded 123.3 mm of rain so far this month, compared with the normal 15.1 mm, a surplus of 108.2 mm or around 717%. Nearly half of the month’s total rainfall was recorded during the 24-hour period ending Friday morning.
The improvement in Delhi’s air quality followed the precipitation, which helped reduce the concentration of airborne pollutants. The city’s average AQI had been recorded at 222, in the poor category, at 4 pm on Thursday before dropping to 90 by 9.30 am on Friday. The CPCB classifies AQI readings from 51 to 100 as satisfactory and readings from 201 to 300 as poor.
The rainfall also brought a marked change in daytime temperatures. Delhi recorded a maximum temperature of 25.4°C at Safdarjung on Thursday, 5.6 degrees below normal and the lowest maximum temperature for an October day in four years. The last lower maximum temperature was recorded on October 8, 2022, when it stood at 23.4°C.
The minimum temperature did not fall by a similar margin. It was 17.2°C on Friday, 1.1 degrees above normal. According to the weather explanation cited in the report, cloud cover and high humidity can restrict the loss of heat from the surface and limit the fall in night-time temperatures.
An active Western Disturbance was the primary weather system responsible for the rainfall over Delhi and other parts of northwest India, according to India Meteorological Department officials. These eastward-moving systems originate in the Mediterranean region and adjoining areas before travelling across West Asia and bringing moisture into northwest India.
Western Disturbances can produce cloud cover, rain and thunderstorms over the plains, and snowfall over the western Himalayan region during winter. The system triggered widespread rainfall across parts of Haryana, Uttar Pradesh, Uttarakhand and adjoining areas.
The IMD also referred to the remnant depression of Very Severe Cyclonic Storm ‘Arnab’, which was located over Chhattisgarh and adjoining Odisha on Thursday and was expected to weaken into a well-marked low-pressure area. The remnant was affecting parts of central and eastern India, while the Western Disturbance was driving the rainfall over northwest India, including Delhi.
The IMD forecast further spells of light to moderate rain with thunderstorms and lightning on Friday and issued an orange alert for the entire city. It forecast partly cloudy skies on Saturday, followed by mainly clear skies from Sunday.
