Altogether 120 trees fell across the city during Monday’s storm, a number that has shocked naturalists who said too much concrete and encroachments around the surface roots of trees were making them vulnerable.

A senior official of the Kolkata Municipal Corporation (KMC), the custodian of the city’s public spaces, said a pre-monsoon storm rarely felled so many trees.

The average speed of Monday’s storm was 45km per hour (kmph) with gusts of wind reaching 77kmph around 8.59pm, the weather department said. The peak speed sustained for less than a minute. According to the India Meteorological Department (IMD), there were several gusts of wind that crossed 50kmph.

At least some of the trees that fell had large canopies, of the type that provides a welcome shade to commuters during summer. Calcutta went through a long phase of extreme heat and high temperatures in the past few weeks. A good number of Krishnachura and Kadam trees were among those uprooted.

The KMC official said alerts about uprooted trees came in every few minutes till past 1am on Tuesday. Things became clearer in the morning.

“We had to deploy 14 teams across the city to clear the trees. Our primary target is to remove the trees that blocked traffic. About 50 per cent of the fallen trees have been removed. The rest are likely to be cleared by Wednesday,” said the official.

Hydraulic ladders were used to chop off broken branches.

In some places, like near Sovabazar Metro station, trees fell and blocked roads for some time. A police officer said fallen trees blocked a portion of Southern Avenue and Ballygunge Place after the storm. They were removed after some time.

Green activist Bonani Kakkar said the fall of so many trees may not be natural. Human activities might have aided their fall.

“We have placed paver blocks so close to trees that they have buried the surface roots. Besides, hawkers have set up stalls in ways that have inhibited the natural growth of trees,” said Kakkar, founder member of PUBLIC, an NGO that works for environmental causes.

“I think it is time that the KMC starts undoing the damage by removing the concrete from around the trees.”

Naturalists said surface roots provide strength and gripping power to trees and help them withstand strong winds. If surface roots are not able to spread, the trees become vulnerable to strong winds.

The fall of so many trees, especially ones with large canopies, means a loss of what has grown over many years. Even if a sapling is planted, it will take decades to provide the canopy.

Scientists told The Telegraph recently that the loss of green cover along with the diminishing green open spaces and filling up of water bodies are making the heat more unbearable.

A green cover has a cooling effect whereas concrete and built-up areas trap and radiate heat back.