Three spells wipe out rain deficit till Aug, Kolkata & Bengal now eye monsoon surplus
Times of India | 17 September 2024
Kolkata: Three major spells of rain in the last one-and-a-half months have wiped out the narrow seasonal rain deficit till Aug in south Bengal and Kolkata, and another spell could even lead to a monsoon surplus, meteorologists feel.
South Bengal's normal rainfall figure is 1,326mm. Kolkata's figure is counted separately, which is why its normal monsoon count is a shade higher, at 1,345mm.Between Sept 1 and 16, Kolkata received 184.8mm rain, against a normal of 158.4mm for that period, which has helped the seasonal count reach the normal mark. South Bengal, in fact, has received 245.2mm rain in Sept so far against a normal of 140.1mm. In terms of overall monsoon count, Kolkata has, till now, received 83% rain already.
While Kolkata has received 1122.8mm rain between June 1 and Sept 16, the normal count is 1192.7mm. It's a slender shortfall which, in meteorological terms, is taken to be "normal". South Bengal has received 1032.3mm rain against a normal count of 1041.1mm — also "normal".
"Three major low-pressure systems over Bay of Bengal, which developed into depressions, triggered moderate to heavy rain across south Bengal in the last five weeks," said H R Biswas, weather scientist, Regional Meteorological Centre (RMC), Alipore. "The first one was on Aug 2, and led to heavy, widespread rain. It was followed by another in the last week of Aug and the current one that formed near the Bengal-Bangladesh coast, sailed into south Bengal, triggering steady drizzles and heavy spells. The narrow deficit has been wiped out and south Bengal and Kolkata could end the season with an excess count."
Between 2018 and 2022, Kolkata had a monsoon rain deficit in four years. Only 2021 was a surplus year.
Kolkata received over 90mm rain on Saturday and Sunday. In Aug, Kolkata had a healthy excess rain of more than 30%. The seasonal deficit had narrowed down to just 7%, which is taken to be normal. While the normal rain count for Aug in Kolkata is 364mm, the city had received 466.6mm by Aug 28, following multiple heavy spells.
The Aug rain excess follows three successive years of deficit for the month.
Kolkata had a deficit of 49% in June. Even though the city received more showers in July, the month had ended with a seasonal deficit of 30%. Between June 1 and July 22, Kolkata received 386mm rain against a normal count of 552mm, a deficit of 30%. The July deficit in south Bengal was 28%.
Between 2010 and 2017, Kolkata received less than normal rainfall in July on five occasions. It doesn't necessarily indicate a deficiency for the season, though, said Biswas. "Even though the seasonal deficiency was high till July, systems formed at regular intervals and led to rain, helping wipe out the deficit. August is also peak monsoon season and it often rains heavily in September. This month has seen good showers so far and we still have two weeks to go," he added.
This year, monsoon had set in in Kolkata on June 22. "While monsoon arrived late, the monsoon trough remained weak and often moved away from south Bengal and remained stationed across north Bengal, triggering heavy rain there. There were few low-pressure systems over Bay of Bengal that could trigger consistent rain, keeping the rain count low. Since early Aug, the trend changed and the trough started hovering over south Bengal more often, pushing the rain count up," Biswas explained.