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Lockdown, increased western disturbances may have led to cooler start to summer in Delhi
New Delhi Delhi is experiencing an unusually cool summer this year. Compared to the average temperature recorded in the national capital since 1980 between March
New Delhi Delhi is experiencing an unusually cool summer this year. Compared to the average temperature recorded in the national capital since 1980 between March and May, the city’s average temperature has been three to six degrees lower this year in the same period, researchers observed.
Limited industrial and commercial activities and vehicular movement because of the nationwide lockdown, along with an increased number of western disturbances this year, could be the reasons behind this change, environment experts said.
Two researchers, Mudit Kapoor, an associate professor of economics at the Indian Statistical Institute (Delhi Unit), and Shamika Ravi, a senior fellow at Brookings Institute, compared Delhi’s average daily temperature from 1980 to 2017 and marked the deviation against 2018, 2019 and 2020.
The researchers observed that this year, between March and May 5, the temperature was three to six degrees lower than the average.
“We compared the temperatures of Delhi, Ahmadabad, Bengaluru, Chennai, Kolkata, Mumbai and Lucknow via a visual presentation. We marked the average temperature of a particular day based on data from 1980 to 2017. We marked any recording above this average in red and any recording below this average in blue for the years 2018, 2019 and 2020,” Kapoor said.
He said, “In Delhi, April 2019, was very hot compared to the average April, but April 2020 is much cooler.”
While the researchers have only made these observations, and are yet to come up with an analysis of the reasons behind the variation in temperature, they are not ruling out the effect of the 49-day nationwide lockdown to control the Covid-19 pandemic, which has restricted industrial and commercial activities in the city and limited vehicular movement on roads.
“It has been an unusual year. Compared to the average temperature (from 1980 to 2017) in Delhi, this year’s lower temperatures so far are an anomaly. This might be because of the lockdown,” Ravi said.
Experts are divided over the reasons behind the dip in temperatures in the city. Some credit the increased number of western disturbances that brought intermittent wet spells through March, April and even the first week of May for the comparatively low temperature. Others are not ruling out the possibility of lower pollution levels in the Capital.
Scientists at the India Meteorological Department (IMD) said Delhi received six WDs in March and six in April, which is unlikely for these months. This trend, however, began from January, when nine WDs passed Delhi, and seven crossed in February.
On May 10, thunderstorm and light rain in certain parts of Delhi-NCR also brought down the temperature. The IMD forecast has predicted cloudy weather for the week, with maximum temperature hovering between 34 degrees Celsius and 39 degrees Celsius.
“There has been an increased effect of WDs in the whole of north-west India, which has kept the temperature in Delhi lower than usual this year. By this time of the year, the normal temperature touches 40 degrees Celsius, but the mercury is yet to rise,” Kuldeep Srivastava, head of the IMD’s regional weather forecasting centre, said.
He added, “We have also noticed that even when it doesn’t rain, clouds hover over the city after the WDs pass, which does not allow the temperature to rise.”
In the summer forecast issued in February, the IMD had indicated that the average temperature in Delhi from March to May is likely to be warmer than normal by 0.5-1 degree Celsius.
Other experts said that though a proper analysis is yet to prove the connection between the lockdown and the lower temperature levels this time, there is scientific proof that vehicular and industrial emissions add to the heat levels of the city.
Anumita Roychowdhury, executive director (research and advocacy) at the Centre for Science and Environment (CSE), said the pollution levels in Delhi and NCR have remained in the green zone for this duration and its positive impact will surely be visible.
“These are such unique circumstances; it is like Earth is in repair mode. We know that emissions from vehicles and industries add to the heat island effect, which increases temperatures in urban centres. It is highly possible that we are benefitting from the restriction in emissions,” Roychowdhury said.
