NEW DELHI: Delhi has witnessed seven heavy rain events this monsoon season so far, the highest in a decade, and these spells account for more than 60 percent of the rainfall recorded in the city, according to the India Meteorological Department data.
Experts say the increase in the number of heavy rain events in many parts of the country is directly linked to climate change.
Rainfall recorded below 15 mm is considered light, between 15 and 64.5 mm is moderate, between 64.5 mm and 115.5 mm is heavy, between 115.6 and 204.4 is very heavy.
Anything above 204.4 mm is considered extremely heavy rainfall.
Normally, Delhi records just one or two such events during the entire season, said senior IMD scientist RK Jenamani.
"The number of 'heavy rain' days this year is very high as compared to previous years.
Most of the rainfall -- around 60 to 70 percent of it -- has come from the heavy spells," he told PTI.
The capital recorded three spells of heavy rain in July -- 69.6 mm on July 19; 100 mm on July 27 and 72 mm on July 30.
While one heavy such episode occurred last month -- 138.8 mm of rainfall on August 21, Delhi has already witnessed three such events this month -- 112.1 mm on September 1; 117.7 mm on September 2 and 94.7 mm September 11 (Saturday).
Altogether, the "heavy rain" events account for 64 percent of the rainfall recorded this monsoon season till Saturday morning.
Delhi had recorded three heavy rain spells in the 2020 monsoon season, and zero in 2019 and 2018.
The city witnessed two such episodes in 2017, zero in 2016, two in 2015, one in 2014, three in 2013, zero in 2012 and one in 2011, according to IMD data.
"Observations of the last 30 years have shown that the number of heavy rain events has increased. It is both based on data and projections.
So, there is no doubt that there are going to be more heavy rainfall days and longer dry spells (in the future).
However, the overall rainfall amount may not change," former IMD director general Ajit Tyagi said.
"There is natural variability also. No two monsoons are the same. If you go up to 50 years in the past, there used to be drought years and flood years.
Climate change is accentuating the natural variability of any weather system in terms of space, time and intensity. But individual events cannot be attributed to it entirely," he told PTI.
He, however, said that up to 50 mm rainfall causing flooding in cities like Delhi and Gurgaon cannot be linked to the climate crisis.
"It is because of our bad planning."
"Going ahead, cities should be planned in a way that they are able to cope with 150 mm to 200 mm of rainfall in a day," Tyagi added.
Mahesh Palawat, vice president of Skymet Weather, a private forecasting agency, said global conditions such as ENSO neutral conditions, lower sea surface temperature in east and central-Pacific ocean, neutral Indian Ocean Dipole and the Madden-Julian oscillation passing through the Indian Ocean were favourable for good rainfall in September.
"So, it depends year to year. But climate change has started affecting the overall monsoon pattern," he said.
"The number of rainy days has reduced over the years, and there has been an increase in extreme weather events. We have been recording short and intense bouts of rain, sometimes around 100 mm rainfall in just 24 hours.
In the past, this much precipitation would occur over a period of 10 to 15 days," he said.
A highly unusual monsoon season this year has yielded 1,100 mm rainfall in Delhi so far, the highest in 46 years, and almost double the precipitation recorded last year, according to the IMD.
The figures are subject to change as more rainfall is predicted in the city.
Normally, Delhi records 653.6 mm of rainfall during the monsoon season, according to the IMD.
Between June 1, when the monsoon season starts, and September 11, it gets 590.2mm of rainfall.