Delhi witnessed a dramatic improvement in air quality on Friday after overnight rainfall brought down pollution levels and temperatures across the national capital. The Air Quality Index (AQI) dropped from 363 on Thursday morning to 78 on Friday morning, moving from the severe category to the satisfactory category within 24 hours, according to data provided by AQI.in.
The widespread rainfall also brought an early winter-like chill to Delhi, offering relief from the relatively warmer conditions experienced earlier in the week.
The downpour was significant enough to make Friday the wettest October day in Delhi in four years. According to India Meteorological Department (IMD) data, the Safdarjung weather station recorded 61.4 mm of rainfall in the 24-hour period ending Friday morning.
What caused the sudden rainfall in Delhi?
According to the IMD, the unusual weather conditions resulted from the interaction of multiple weather systems.
A western disturbance positioned over the Western Himalayas combined with an induced cyclonic circulation over South Punjab. Meanwhile, winds originating from the Bay of Bengal, influenced by the remnants of Cyclone Arnab, also reached Delhi.
These weather systems converged over Delhi-NCR and neighbouring regions, resulting in widespread and unseasonal rainfall.
Mahesh Palawat, Vice President of Meteorology and Climate Change at Skymet Weather Services, explained that the interaction between the western disturbance, cyclonic circulation and winds from the Bay of Bengal contributed to the rainfall across northwest India, including Delhi, Punjab, Haryana and East Rajasthan.
He noted that such rainfall is unusual for this time of the year, as winter rainfall in northwest India generally occurs under the influence of western disturbances during November and December.
Delhi temperatures drop after overnight rain
The rainfall also resulted in a significant decline in temperatures across the national capital.
Maximum temperatures fell by 4 to 6 degrees Celsius over a 24-hour period, remaining considerably below seasonal averages.
Delhi’s Safdarjung weather station recorded a maximum temperature of 25.4 degrees Celsius, which was 5.6 degrees below normal. It was also the lowest maximum temperature recorded for an October day in four years.
Minimum temperatures across Delhi remained between 15 degrees Celsius and 18 degrees Celsius.
Safdarjung recorded a minimum temperature of 17.2 degrees Celsius, around 1.1 degrees above normal. Meanwhile, Palam registered 15.4 degrees Celsius and the Ridge recorded 16.8 degrees Celsius.
The IMD forecast that maximum temperatures would remain between 24 and 26 degrees Celsius on October 30 before gradually rising towards normal levels over the following days.
Will Delhi’s air quality deteriorate again?
Despite the significant improvement, the relief from pollution may not last long.
Mahesh Palawat said widespread rainfall had helped bring down pollutants and improve air quality across the region. However, he cautioned that pollution levels could increase again once the skies clear and temperatures rise.
According to him, air quality could return to the poor category after a day or two as weather conditions change. He also indicated that pollution could deteriorate further during the second week of November as Diwali approaches.
The improvement in AQI, therefore, offers temporary relief rather than a permanent solution to Delhi’s pollution problem.
IMD’s weather forecast for Delhi and other states
According to the IMD, weather conditions across Delhi-NCR are expected to gradually become drier.
The national capital is likely to experience partly cloudy skies on October 31 and November 1, followed by clearer conditions. Daytime temperatures are expected to return to the 28 to 31 degrees Celsius range.
Meanwhile, several other parts of the country are likely to experience rainfall during the coming week.
In South Peninsular India, a low-pressure system over the South Andaman Sea is expected to develop into a depression over the Bay of Bengal. This could bring isolated very heavy rainfall to Coastal Andhra Pradesh and Yanam on November 2 and 3, along with widespread showers across Karnataka, Kerala and Tamil Nadu.
In Central India, Chhattisgarh is expected to receive fairly widespread rainfall, with isolated heavy showers accompanied by thunderstorms on November 2.
Parts of Bihar, Jharkhand, Odisha and Arunachal Pradesh are also likely to receive scattered light to moderate rainfall during early November.
As Delhi moves towards clearer weather conditions, the improvement in air quality will depend partly on how atmospheric conditions evolve after the recent spell of rain.