Bengal floods: Trajectory change of low-pressure system led to havoc

KOLKATA: Devastating rain that flooded the plains and hills of north Bengal was brought by an unexpected change in the trajectory of a low-pressure system triggered by the retreating monsoon, meteorologists have said.

The system, which formed over the Bay of Bengal on Sept 30, made landfall in Odisha as a depression and was moving north-northwest towards Chhattisgarh when it suddenly recurved towards north Bihar, coming dangerously close to north Bengal.

“Even though not very intense, such systems cover a wide region. North Bengal fell within the periphery of this one, which explains the heavy rain. In fact, Kolkata, too, continues to be impacted by the same system,” a meteorologist said.

Sourish Bandopadhyay, a scientist at the regional meteorological centre, said, “Clouds kept floating into the hills and over Dooars. Extremely heavy rain, over 200mm in around 24 hours, occurred in some parts of Darjeeling, Alipurduar, Kalimpong, and Jalpaiguri on Friday and Saturday. Its intensity reduced Sunday.”

Darjeeling recorded 261mm of rain in 24 hours till 8 am on Sunday, followed by Cooch Behar (192mm), Jalpaiguri (172mm), and Bagdogra-Siliguri (134mm). Excess water flowing through rivers entering Bengal from Sikkim and Bhutan only worsened the devastation.

“Since monsoon is now retreating from north India, strong westerly winds diverted the system towards north Bihar, bringing it closer to north Bengal. It was prevented from advancing into central India, which is the usual path for such systems... The ‘recurve’ was unexpected but not unusual,” said a meteorologist. In its current state as a cyclonic circulation, the system still covers a wide area — across north Bihar, hills of Bengal, and eastern Nepal.

“Rain will continue in these areas. The system is likely to move towards Bangladesh, though it may lose steam over the next 48 hours,” the meteorologist added.