Delhi crawls as rain in past week nine times the normal

Consistent rain has led to a sharp drop in daytime temperatures, with Thursday and Friday, when most of the rain took place, 7-8°C cooler than normal

Delhi has received almost nine times the usual amount of rain in the week ended September 24, making the month the 30th rainiest since 1901, despite an 83% deficit in rainfall up to September 14, according to data.

Vehicles wade through a waterlogged stretch in heavy rain on the NH-48 service road near Narsinghpur village in Gurugram on Saturday. (Parveen Kumar/HT Photo)

Rainfall was recorded in Delhi for the third consecutive day on Saturday, with incessant downpour causing traffic snarls and waterlogging in many areas. More rainfall has been predicted by the India Meteorological Department (IMD) over the next two days.

Consistent rain has led to a sharp drop in daytime temperatures, with Thursday and Friday, when most of the rain took place, 7-8°C cooler than normal. September 22 and 23 have been the second coldest and coldest by maximum temperature, respectively, since 1951.

The national capital recorded a drop in mercury on Saturday, as the maximum temperature settled at 27.2 degrees Celsius at the Safdarjung station, seven notches below normal.

In the week ended 8.30am on September 24, Delhi received 107.7mm rainfall, according to the gridded dataset of IMD. It was 8.7 times the average rain in this week in the 1961-2010 period. The rainfall for this week in 2022 is the 5th highest since 1901, the earliest year for which the weather department has data.

To be sure, these ranks can be slightly different for individual weather stations in Delhi, as the gridded dataset also uses data from neighbouring stations to arrive at an average.

The rain in the past week has turned the 83% deficit in the first two weeks of September to a 34% surplus by the morning of September 24. What looked like a dry September following a very dry August (9th driest since 1901) is now the 30th rainiest since 1901.

As much as 78% of the 138mm rain this month has taken place since 8.30am on September 20. The average rain in the past four days was 27.6mm, 5.4mm, 51mm, and 23mm, the 2nd highest, 13th highest, highest, and 6th highest, respectively, since 1901 for those days.

As a result, these four days were also much cooler than normal. The maximum temperature from September 20 to September 23 was 33.3°C, 31.6°C, 27.5°C, and 26.7°C. These are 1.5°C, 3.3°C, 7.3°C, and 8°C cooler than the 1951-80 average for those days, considered the normal for daytime temperature. In terms of ranking, these days were the 12th, 5th , 2nd , and coldest for those days since 1951. The average maximum for the past week (31.7°C) too, was 2.9°C cooler than normal. This was the 3rd coldest week ending September 23 since 1951.

Minimum temperatures have also decreased, but not as rapidly. This is because an overcast sky does not allow the earth to release the heat trapped during the day. The week ended September 24 was the 18th hottest since 1951 and 0.69 degrees warmer than the normal of 23.78°C. It means that the hot trends from early September have persisted in night temperatures. The first 24 days of September were still the 2nd warmest since 1901.

While the rain in the past week might have cooled days and covered the September rainfall deficit, it has not completely removed the deficit Delhi was carrying in overall southwest monsoon rain. Since there was an 81% deficit in August, Delhi’s wettest month, the rain of the past week has only reduced the overall monsoon deficit to 29%. It is still an improvement over the 41% deficit prevailing as late as September 22.

The weather department had issued a “yellow alert” for Saturday, warning people about moderate rain at most places in Delhi, with heavy rain at a couple of locations. Traffic snarls were reported from different parts of the national capital. The Delhi Traffic Police advised commuters to plan their journey accordingly.