Why in News?

• The Earth Sciences Secretary has announced that the India Meteorological Department (IMD) has decided to revise the normal onset and withdrawal dates for the monsoon in some parts of the country from this year.

Highlights:

• The four-month southwest monsoon season, which brings as much as 70 per cent of the country’s annual rainfall, officially begins on June 1, with the onset over Kerala, and ends on September 30.
• The monsoon takes about a month and half after onset on the Kerala coast to cover the entire country and about a month, beginning from the north-western parts of the country on September 1, to withdraw completely.
• Although the June 1 date for the onset of the monsoon on the Kerala coast is unlikely to be changed, the dates for onset in many other parts of the country are expected to be revised. Adjustments are likely to be made for many other parts of the country as well. Similar changes are expected in the withdrawal dates.
• Effectively, the monsoon is now expected to have later arrival and withdrawal dates in most parts of the country.

Reason for Changes:

• The Main Reason for the revision in the normal dates is the changes in precipitation patterns that have been taking place over the last many years.
• In the last 13 years, for example, only once has the onset over the Kerala coast happened on June 1. While two or three days of earlier or later onset falls within the yearly variability, in several years the onset happened five to seven days late.
• Similarly, the commencement of withdrawal has happened in the first week of September only twice during this period, and last year, the withdrawal started as late as October 9 and was completed in around just a week.
• One of the significant changes being noticed is that rainfall is getting increasingly concentrated within a narrow band of days within the monsoon season. So, there are extremely wet days followed by prolonged periods of dry days.
• Areas that have traditionally received plenty of rainfall are often remaining dry, while places that are not expected to get a lot of monsoon rain have sometimes been getting flooded.

Impact of the Changes:

• New dates will likely nudge farmers in some parts of the country to make slight adjustments in the time of sowing their crops.
• If the rainfall over the rice-growing regions occurs very late, then the transplantation of rice would be affected, which in turn could hit the crop yield.
• Water management agencies managing the dams in the central plains, should now expect more rain only in the latter part of June.
• Instead of planning only until the start of June, they would now be prompted to preserve and hold on to some water until later in the month.
• The change in normal dates of the onset and withdrawal of the monsoon would help people understand when to expect rains, and to plan their activities accordingly.