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Tuesday, September 21, 2021

Heat wave & delayed monsoon to heavy rain: Why July saw extreme weather in Delhi

Five days in July witnessed heat waves, when temperatures soared between 41 and 43 degrees Celsius.

Written by Abhinaya Harigovind | New Delhi |
Updated: August 2, 2021 10:08:36 am
Waterlogging at Yamuna Bazar after heavy rainfall on Sunday. (Express Photo: Praveen Khanna)

July, with a delayed monsoon followed by heavy rainfall, saw weather extremes that are uncommon as it oscillated from heat waves to temperatures significantly lower than normal.

Five days in July witnessed heat waves, when temperatures soared between 41 and 43 degrees Celsius. This is uncharacteristic for the month, as monsoons rains usually reach Delhi on June 27. According to R K Jenamani, scientist at India Meteorological Department (IMD), the heat wave was an extension of the previous summer months and went along with the delay in the onset of the monsoon over Northwest India. Monsoon was deficient till around July 12, but Northwest India got a good spell of rainfall later, he said.

A few areas saw localised heavy rainfall over the last few days. For instance, the Ridge weather station saw 130 mm of rainfall between 8.30 am on Saturday and 8.30 am on Sunday, while the figure for the Safdarjung station for the same time period was a much lower 28.2 mm. “This monsoon is interesting. Short, major spells of rainfall were seen,” Jenamani said.

Data from the IMD shows that rainfall was recorded on 16 days in July, but heavy rainfall (falling between 64.5 mm and 115.5 mm) was seen only on three days.

A total of 507.01 mm of rainfall was recorded at Safdarjung in July. Normal rainfall for the month at Safdarjung is considered to be 210.6 mm, making this year’s figure 141% above normal.

On the excess rainfall in July, Sathi Devi, head of IMD National Weather Forecasting Centre, said “This is not unusual. In a short period, we are seeing intense rainfall. There is a change in pattern,” she said.

The heat wave at the start of the month can be attributed to the hiatus in the monsoon, though it was not a prolonged heat wave, Sathi Devi said. Once the monsoon set in, good rainfall activity was propelled by the presence of synoptic systems like monsoon troughs and low pressure areas. Monsoon trough, a feature of the season, passed through Northwest India particularly over the last week, which is favourable for heavy rainfall. There was a low pressure area over Haryana as well recently, contributing to rainfall activity, she said.

As per IMD, the monsoon trough is an elongated low pressure area. For the coming week, the IMD has forecast moderate to heavy rainfall and thundershowers.

Waterlogging at underpasses

Following morning showers, three underpasses in Delhi were waterlogged on Sunday. The Delhi Traffic police asked commuters to avoid Zakhira Underpass, Azadpur underpass and Shakti Nagar underpass temporarily.

Earlier this year, the Public Works Department had issued a circular saying that in order to avoid accidents, traffic around underpasses in Delhi will be stopped temporarily if the area is flooded and the depth of the water crosses 20 cm.

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