Even when the monsoon arrives on paper, Gangetic Bengal is left short of rain in June and July. Alongside climate change and nature's other whims, a group of scientists in the city is now pointing to a new reason for this "stinginess". Their research also reveals a new side of the Sundarbans mangrove forest.

In a new study, a team of researchers at the Bose Institute has shown that the Sundarbans mangrove forest protects a large part of southern Bengal, including Kolkata, not only from sea storms but also from air pollution. But this work also has a negative effect: the scientists say that as the mangrove forest swallows airborne carbon particles, the rhythm of the monsoon is being thrown off. Their paper has been published in the international science journal Chemosphere.

The team, made up of established scientists such as Sibaji Raha, Abhijit Chattopadhyay, Sanat Kumar Das and Sanjay Ghosh and young researchers such as Abhinandan Ghosh and Arindam Roy, found that for summer jhum cultivation, communities in areas next to the Eastern Ghats indiscriminately burn crop residues after harvest. The ash and carbon particles drift towards Bengal on the southerly wind but in the end cannot enter Bengal's air, because salt particles in the Sundarbans air and various organic gases released by the mangroves absorb them. As a result, the ash and fine carbon particles cannot reach Kolkata.

Is the monsoon's "nature" changing because the mangroves absorb these carbon particles? Many environmentalists say rainfall in June and July has been falling for several years, and a change in the monsoon's character is being seen. But many researchers are still unsure whether that change is permanent.

Abhijit Chattopadhyay said the reaction with carbon particles changes the character of the salt particles in the air, and this is affecting the climate. Normally, salt particles quickly take up water and help form clouds. But after reacting with carbon, the salt particles in the sea air are losing that natural character. Because the whole process happens at the end of summer and the start of the monsoon, it is harming monsoon rainfall.

How great a role the Sundarbans mangrove forest plays as a shield for southern Bengal, including Kolkata, was felt sharply during the recent Cyclone Bulbul. Environmentalists and meteorologists say that without the mangrove wall, the extremely severe cyclone would have devastated a vast stretch of coastal Bengal, including Kolkata. The mangroves took the blow and saved the city and a wide area around it, but the Sundarbans mangrove forest was badly damaged, and the forest department has begun work to restore it.

Abhijit Chattopadhyay said that to protect Kolkata from pollution by drifting burnt carbon particles, the mangroves must be expanded, and jhum cultivation in the Eastern Ghats region must be reined in as well.

Source: Anandabazar. First published in Bengali on The Agro News.