Delhi Air Quality Drops To 78 After Record Rain Brings Winter Chill

Delhi experienced a shift in weather conditions as rainfall ushered in low temperatures and improved air quality on Friday. Dispelling pollution concerns and improving visibility briefly, the downpour provided residents with respite from the pollution the national capital is experiencing. As per data provided on AQI.in, the Air Quality Index (AQI) fell from 363 on Thursday morning to 78 on Friday morning. This implies that the rainfall contributed to a sharp improvement in the capital's air quality within 24 hours, moving from the severe pollution range to the satisfactory category.

The changing weather also brought chilly winter conditions. Cloud cover, heavy rainfall and cooler temperatures have made the weather noticeably more pleasant as opposed to the warmer days earlier this week. The downpour, in fact, also proved to be record-breaking, as Delhi recorded its wettest October day in four years. 

READ | Delhi Logs Coldest October Day In 4 Years Amid Cyclone Arnab

According to India Meteorological Department (IMD) data, the Safdarjung weather station recorded 61.4 mm of rainfall in the 24-hour period leading up to Friday morning.

Meteorological Conditions And Causes

According to IMD, this rare weather phenomenon was triggered by the convergence of multiple systems. A western disturbance positioned over the Western Himalayas combined with an induced cyclonic circulation over South Punjab. Winds from the Bay of Bengal, channelled by the remnants of a cyclone, reached all the way up to Delhi, converging over the NCR and adjoining areas.

To understand the mechanics better, NDTV spoke to Mahesh Palawat, Vice President of Meteorology and Climate Change at Skymet Weather Services, who said, "The rainfall over Northwest India, including Delhi, Punjab, Haryana, East Rajasthan, and parts of Uttar Pradesh, can be attributed to a western disturbance over the Western Himalayas and an induced cyclonic circulation over South Punjab. Moreover, winds from the Bay of Bengal, driven by the remnants of Cyclone Arnab, were also reaching up to Delhi." 

READ | Overnight Rain In Delhi Brings Winter Chill, Improves Air Quality

"All these systems converged over Delhi-NCR and adjoining areas, leading to widespread, unseasonal rainfall. Usually, winter rains occur in the wake of western disturbances, mostly in November and December. But this time, we have seen heavy rainfall to the tune of 50 to 60 mm over Delhi," he added.

Temperature Drop And Morning Data

The overnight rainfall brought an early winter-like chill to the national capital. 

Maximum Temperatures:

Maximum temperatures dropped sharply by 4 degrees Celsius to 6 degrees Celsius over a 24-hour period, placing them markedly below normal. Delhi's base weather station at Safdarjung recorded a daytime high of 25.4 degrees Celsius (which was a sharp 5.6 degrees Celsius below seasonal norms), marking the coldest October daytime high in four years.

Minimum Temperatures:

Minimum temperatures settled in the range of 15 degrees Celsius to 18 degrees Celsius across Delhi. Specifically, Safdarjung recorded a minimum temperature of 17.2 degrees Celsius (about 1.1 degrees Celsius above normal), while other stations like Palam recorded 15.4 degrees Celsius and the Ridge recorded 16.8 degrees Celsius.

Upcoming Trend: 

The IMD forecasted that maximum temperatures would stay low (ranging between 24 degrees Celsius and 26 degrees Celsius on October 30) before gradually climbing back toward normal ranges (26 degrees Celsius to 31 degrees Celsius) over the subsequent days as skies clear up into early November.

Pollution Reduction And Morning Air Quality Data

The widespread showers delivered immediate respite from the capital's severe pollution crisis: Delhi's Air Quality Index (AQI) plummeted dramatically from 363 down to 78 within a 24-hour window, moving directly from the severe range into the satisfactory category.

However, experts note this relief will be temporary. 

"I think that pollutants will go down and pollution will improve because the rain was widespread. However, it was not a very heavy downpour, but still, there will be some relief and respite. But after a day or two, when the sun comes up, the sky clears up, and temperatures rise, pollution will make a comeback. So, it will be in the poor category, and by the second week of November, it will further deteriorate as Diwali approaches," Palawat said. 

IMD Rain Forecast For The Coming Week And Pan-India Outlook

According to the IMD, weather conditions over Delhi-NCR will gradually turn drier with partly cloudy skies on October 31 and November 1, followed by clearer conditions and a return of daytime temperatures to the 28 degrees Celsius -31 degrees Celsius range.

Across the rest of India, the forecast for the coming week includes:

South Peninsular India: A low-pressure system over the South Andaman Sea is expected to concentrate into a depression over the Bay of Bengal, bringing very heavy isolated rainfall to Coastal Andhra Pradesh and Yanam on November 2nd and 3rd, alongside widespread rain across Karnataka, Kerala, and Tamil Nadu.

Central India: Chhattisgarh is slated for fairly widespread rainfall and isolated heavy downpours accompanied by thunderstorms on November 2.

East and Northeast India: Light to moderate scattered rainfall will continue over parts of Bihar, Jharkhand, Odisha, and Arunachal Pradesh through early November.

As the rain clears out, atmospheric conditions may worsen if winds slow down, causing air pollution to come back. For the time being, however, the sudden weather shift gives Delhi residents a welcome break from both unseasonal warmth and hazardous air quality.