Met dept to change official Monsoon dates

Met dept to change official Monsoon dates
Neha Lalchandani, TNN Oct 4, 2011, 04.52AM IST
Tags:Scientist|IMD|Ajit Tyagi
NEW DELHI: Armed with exhaustive data on rainfall from several more stations in the past 30 years, the Indian Meteorological Department is working on an analysis that will see a change in the date of monsoon onset and withdrawal over the country. Since 2006, the monsoon's retreat has been commencing between September 21 and September 30 against a normal date of September 1.

A report on India's climate profile by IMD director-general Ajit Tyagi and Dr S D Attri reveals that between 1941 and 2000, there has been a slight shift in monsoon activity with late onset and late withdrawal and a general increase in duration by about a week. More evidently, as IMD set specific criteria for onset and withdrawal four-five years ago, making it mandatory for all conditions to be met before they declare onset or withdrawal, the withdrawal date has shifted by two-three weeks.


"As we have started following the criteria, we have new dates for onset and withdrawal. We will have to test these against the normal, work out variability and see if changes are required. The process has started but we need to have experts ratify our findings before the formal dates can be declared. The process may take a year or so," said Tyagi.

Between 1971 and 2000, Jammu and Kashmir saw a standard deviation of 14 days in the onset of monsoon from the normal date. West and northwest India have seen onset delayed by an average of 1.5 weeks.

Withdrawal dates have also shifted by about one to 1.5 weeks. "A general late onset suggests a shift in the monsoon activity. The duration of the southwest monsoon has also been found to be higher in all meteorological sub-divisions in the past 60 years," said Tyagi.

Dr M Rajeevan, scientist and monsoon expert with the National Atmospheric Research Laboratory, said it was high time that IMD proposed such changes. "The normal dates for monsoon activity were set several years ago and there has been a marked change in circulation, dates etc that should now be updated. For instance, onset of monsoon has been steadily getting delayed over the eastern parts of central India. Such changes are due to a natural variability and not a result of global warming," he said.

Officials also said a change had also been recorded in the total rainfall across various regions, though there had not been a significant change in the overall rainfall for the country. "In the four months of monsoon, we have seen large regional variation with east getting lesser and west getting more rainfall," said Tyagi.

In June, west and southwest India have recorded a significant increase in rainfall while central and eastern parts have shown a significant decrease. In July, central and peninsular India have shown a decrease while northeast India has shown a significant increase.

August has shown a significant increase in rain over Konkan and Goa, Marathwada, Madhya Maharashtra, Vidarbha, west Madhya Pradesh, west Uttar Pradesh and Telengana while September has shown a decrease in average rainfall over Vidarbha, Marathwada and Telengana and an increase for sub-Himalayan West Bengal.