A persistent patter of rain that continued through Friday to soak Delhi and its surrounding regions, delivering an unusually wet December day that shattered long-standing rainfall records and highlighted the unpredictability of the season.
By the end of the day, the city had recorded 42.8mm of rainfall this month, making it the fifth wettest December in Delhi’s recorded history and the rainiest since 1997, or in 27 years, according to data from the India Meteorological Department (IMD).
The rainfall, largely attributed to an active western disturbance interacting with easterly winds, transformed the usual dry chill of December into an anomaly.
Safdarjung, Delhi’s primary weather observatory, recorded 30.2mm of rain in just nine hours between 8.30am and 5.30pm on Friday. This made it the wettest single-day spell in five years, according to IMD data. The city saw 33.5mm rain on December 13, 2019, according to IMD records.
Other weather stations also recorded similarly consistent showers through the day. Pusa logged 35mm of rain between 8.30am and 5.30pm, Delhi University recorded 39mm, Lodhi Road recorded 34.2mm, Ridge saw 33.4mm, while Palam and Ayanagar recorded 31.4mm and 18.1mm respectively.
IMD classifies up to 15.5mm of rainfall in 24 hours as “light rain”, 15.6-64.4mm of rainfall as “moderate”, 64.5-115.5mm as “heavy rainfall” and 115.6-204.4mm as “very heavy rainfall”.
IMD data shows that December’s total rainfall this year has reached levels not seen in nearly three decades.
The last time December rains were this intense was in 1997, when the total monthly precipitation was 71.8mm. Going further back, the highest December rainfall was recorded in 1901 at 77.2mm, followed by 1967 (69.5mm) and 1936 (68.1mm).
“This is unseasonal and remarkable for December,” said an IMD official, explaining that the interaction of two weather systems led to the unusual rainfall. “An active western disturbance is interacting with easterly winds, leading to rainfall and thunderstorms over northwest and central India, including NCR Delhi,” the official said.
According to forecasts, there is more rain yet to come. IMD has issued a yellow alert for Saturday, warning of possible light rain in the early hours and dense fog across the region. Similar alerts are in place for Sunday and Monday, with visibility expected to drop significantly due to lingering moisture.
Mahesh Palawat, vice president at Skymet Weather, said, “There might be some patchy rain on Saturday and the moisture might lead to a dense fog for the next two days.”
IMD has also issued a yellow alert for Sunday and Monday, warning people of a dense fog.
Relief from pollution
The unseasonal showers, however, brought some blessings to the Capital, offering temporary respite from choking air pollution.
The 24-hour average air quality index (AQI) improved from 353 (“very poor”) at 4pm to 325 by 8pm on Friday.
Forecasts suggest that strong northwesterly winds expected on December 30 and 31 could further cleanse the air. “There is a forecast for strong north-westerly winds to influence the region on December 30-31. That might help improve the air quality further,” Palawat said.
The Air Quality Early Warning System (AQEWS) for Delhi has forecast that the AQI may even dip into the “moderate” range over the weekend, before deteriorating again early next week.
“The air quality is likely to be in moderate category on Saturday. The air quality is likely to be in poor category on Sunday. The air quality is likely to be in very poor category on Monday. The outlook for subsequent six days is that the air quality is likely to be in very poor category,” the AQEWS bulletin said on Friday evening.
Grap Stage 3 removed
The Commission for Air Quality Management (CAQM), meanwhile, responded to improving air quality levels by revoking Stage 3 of the Graded Response Action Plan (Grap) on Friday evening.
GRAP 3, which kicks in when AQI exceeds 350, had been in place since December 16. Its removal marks a return to fewer restrictions: schools can resume offline classes for younger students, BS-III petrol and BS-IV diesel vehicles can ply in Delhi and its NCR neighbours, and diesel goods carriers meeting specific criteria can re-enter the city.
