NEW DELHI: The India Meteorological Department (IMD) has come up with a new calendar on onset and withdrawal of the southwest monsoon, especially relevant for agriculture, water and power management, in the country.
The change in schedule followed since 1941 was necessitated keeping in mind the delayed monsoon onset and withdrawal recorded by weather offices in various regions of the country in the last few years.
According to the ‘New Normal Dates of Onset/Progress and Withdrawal of Southwest Monsoon Over India’, monsoon onset over Kerala remains the same on June 1, but the monsoon advance dates over the states like Maharashtra, Gujarat, Madhya Pradesh, Chhattisgarh, Telegana, Andhra Pradesh, Odisha, Jharkhand, Bihar and parts of Uttar Pradesh are delayed by 3-7 days compared to existing normal dates.
“However, over extreme northwest India, the monsoon arrives now little early, July 8, compared to the existing date of July 15. There are, however, appreciable changes in the monsoon withdrawal dates, especially over Northwest and Central India. Monsoon withdraws from NW India almost 7-14 days later from the existing dates. There is no change in the final withdrawal date over south India, October 15,” Ministry of Earth Sciences secretary M Rajeevan said.
The normal onset of monsoon occurs on June 1 and withdrawal starts by September 1, according to IMD, The existing normal monsoon onset and withdrawal dates are based on records of 149 weather stations during the period from 1901 to 1940. “The normal dates of onset are revised based on data during 1961-2019 and normal dates of withdrawal are revised based on data during 1971-2019,” Rajeevan said.
The IMD has designed new objective criteria for defining monsoon onset over the entire country based on daily gridded rainfall data set. The new objective criteria used for deciding monsoon onset/progress dates are designed to closely simulate IMD’s operational onset dates.