Delhi logs most polluted July in seven years despite above-normal rainfall

Delhi ended July with a striking mix of weather extremes, recording its most polluted July in seven years despite witnessing its first 'good' air quality day for the month in nearly a decade. The city also received above-normal monsoon rainfall after a prolonged dry spell and registered its warmest average day and night temperatures in two years.

According to an analysis by the Centre for Research on Energy and Clean Air (CREA), Delhi's average Air Quality Index (AQI) for the first 30 days of July stood at 119, the highest monthly average for July since 2019, when it was 134. The figure marks a sharp deterioration from July last year, when the monthly average AQI was 78.

Even as the monthly average worsened, Delhi recorded its first 'good' air quality day in July in nine years, with the AQI falling to 48. It was also the lowest daily minimum AQI recorded in the month since 2017, when it touched 43.

The city also saw the AQI rise to 261 during the month, the highest daily maximum recorded in July in five years, since it reached 266 in 2021.

Overall, Delhi recorded 15 'moderate' air quality days, 12 'satisfactory' days, two 'poor' days and one 'good' day during July. It did not experience any 'very poor' air quality days.

According to the Central Pollution Control Board (CPCB), an AQI between 0 and 50 is categorised as 'good', 51-100 as 'satisfactory', 101-200 as 'moderate', 201-300 as 'poor', 301-400 as 'very poor' and 401-500 as 'severe'. On Thursday, Delhi's AQI stood at 117, remaining in the 'moderate' category.

Despite an extended break in monsoon activity, rainfall across most weather stations remained above normal for the month.

At Safdarjung, Delhi's base observatory, 254.7 mm of rainfall was recorded in July against the normal of 201.9 mm, an excess of 52.8 mm or 26 per cent. Since the onset of the southwest monsoon, the station has received 296.5 mm of rainfall against the seasonal normal of 276 mm, a surplus of 20.5 mm or 7 per cent.

The Ridge recorded the highest surplus among the city's major observatories, receiving 285.5 mm of rainfall against a normal of 188.5 mm, an excess of 97 mm or 51 per cent. Since the monsoon began, it has received 338.1 mm against the seasonal normal of 249.2 mm, a surplus of 88.9 mm or 36 per cent.

Lodhi Road recorded 274.4 mm of rainfall during July against the normal of 201.9 mm, an excess of 72.5 mm or 36 per cent. Since the onset of the monsoon, the station has received 315.1 mm against a normal of 276 mm, a surplus of 39.1 mm or 14 per cent.

Ayanagar received 210.1 mm during the month against the normal of 178.5 mm, an excess of 31.6 mm or 18 per cent. Since the beginning of the southwest monsoon, it has recorded 303.1 mm against the seasonal normal of 248.4 mm, a surplus of 54.7 mm or 22 per cent.

Palam was the only major observatory to record below-normal rainfall. It received 179.1 mm during July against the normal of 198.2 mm, a deficit of 19.1 mm or 10 per cent. Since the onset of the monsoon, the station has recorded 229.4 mm against the seasonal normal of 267 mm, leaving it 37.6 mm or 14 per cent below normal.

Mahesh Palawat of Skymet Weather attributed the above-normal monthly rainfall despite fewer rainy days to an unusually long break in the monsoon.

"The monsoon witnessed a typical break this season, but instead of lasting five to six days as it usually does, it extended to around 10 to 11 days. As a result, the number of rainy days was lower, though the overall rainfall remained high because a few spells were particularly intense. The first few days of July saw very good monsoon activity, and the last week of the month remained active. In between, there was a prolonged break caused by multiple weather systems, which later triggered episodes of intense rainfall," he said.

The capital also recorded its warmest July in two years, with the average maximum temperature at 35.4°C and the average minimum at 27.7°C. The last time both averages were higher was in 2024, when the average maximum temperature was 35.9°C and the average minimum was 27.8°C.

On Thursday, Safdarjung recorded a maximum temperature of 35.8°C, 1.4°C above normal. Palam recorded 35°C, while Lodhi Road logged 35.3°C. The Ridge recorded 34.8°C and Ayanagar 35.2°C.

Safdarjung received 3.3 mm of rainfall between 8.30 am and 5.30 pm on Thursday, while Palam recorded 3 mm. Lodhi Road received 1.1 mm during the same period after a trace of rainfall earlier in the day. The Ridge recorded 7.6 mm, the highest among the major observatories, while Ayanagar did not receive any rainfall.

With PTI inputs