Why a delayed monsoon is bringing more rain to Delhi

Delhi in July is now witnessing 2-3 intense spells of rain that can now bridge the deficit completely.

The southwest monsoon has been arriving later than usual in Delhi in recent years, even as rainfall in July is exceeding the monthly average of 210.6mm. This means the capital is receiving more spells of intense rainfall, which meteorologists say is not a good sign.

The monsoon arrived in Delhi after the normal onset date of June 27 seven times out of the past 10 years. (File image)

In six out of the past 10 years, July rains over the capital has been higher than the average, according to India Meteorological Department data from 2012 to 2021. This year, too, a delayed monsoon saw Delhi receiving 117.2mm of rainfall in just 24 hours between June 30 and July 1, which has since seen Delhi cross the normal mark in the first 20 days of the month.

The monsoon arrived in Delhi after the normal onset date of June 27 seven times out of the past 10 years, reaching earlier than normal only in 2020 (June 25), 2015 (June 25) and 2013 (June 16). This year, the arrival was declared on June 30, a delay of three days. This trend has meant rainfall Delhi would normally receive towards the end of June has now shifted to early July.

With extreme weather events becoming more common, the onset of the monsoon can fluctuate, according to Mahesh Palawat, vice president of meteorology and climate change at Skymet Weather Services, a private forecaster. However, Delhi in July is now witnessing 2-3 intense spells of rain that can now bridge the deficit completely, he said.

“Last year, too, we witnessed three intense spells of rain and these are enough to push Delhi into excess. This year, too, we have seen three major spells, and they have again pushed Safdarjung in the excess category,” Palawat said. “This is not a good sign as these spells are intense but occur over a short period, not impacting temperature substantially and not recharging the groundwater table either.”

Delhi averaged 246.5mm of rainfall in July over the past decade, higher than normal and considerably higher than the long-period average of 187.3mm between 1981 and 2010, weather bureau data show.

On the flip side, June has averaged 64.1mm of rainfall over the past decade, slightly lower than the normal monthly figure of 65.5mm. This, however, has largely been aided by a spell of 191.9mm of rainfall in 2017, nearly three times the monthly average. June has received below par rainfall in seven out of the past 10 years, data show. This year, too, it received only 24.5mm of rainfall in June, leaving a deficit.

The onset date for the southwest monsoon in Delhi was brought forward to June 27 in 2021 from June 29 earlier.

Delhi is increasingly seeing a delayed onset over the past two decades, which influences the amount of rainfall June or July receive, said RK Jenamani, a scientist at the weather office.

“If the onset is declared in July, it will receive at least a couple of good spells of rainfall and this can push July close to the normal mark,” Jenamani said. “In comparison, we are seeing very little pre-monsoon or monsoon rain in June, but to link it to a shift in the monsoon pattern will require more long-term analysis.”

The Met department classifies the monsoon period as June until September, with Delhi normally receiving a total of 648.9mm of rainfall during these four months. Delhi receives 779mm of rainfall a year. Last monsoon, it recorded 1169.7mm of rainfall, almost double than normal. So far till July 24, Delhi’s monsoon total stands at 255mm.