NEW DELHI: You may be getting summer rains either early or late than the assigned ‘normal’ dates for arrival and withdrawal of monsoon in your cities/states, but the gap is likely to be bridged to an extent from this year as the India Meteorological Department (IMD) will come out with new ‘normal’ reference dates for arrival and withdrawal of south-west monsoon while making its first forecast for 2020 season in April.
Though the normal onset date of summer monsoon for Kerala may remain the same as on June 1, the withdrawal date from north-west India may be delayed by nearly 10 days – it means the normal withdrawal date of the monsoon from north-west India (north Rajasthan, Punjab and Haryana) will be changed from September 1 to September 10.
The four-month monsoon period (June 1 – September 30) will, however, remain the same. Arrival of monsoon in Kerala is considered as an onset date of monsoon for India even if it hits Andaman & Nicobar Islands a few days earlier.
India had been adhering to June 1 and September 1 as ‘normal’ reference dates for onset and withdrawal of monsoon ever since it was last set in 1941 — 79 years ago.
The changes, based on analysis of historical data on changing rainfall pattern across the country, will help farmers, civic agencies, hydro-power plants and disaster management authorities in carrying out better planning of their works during the season.
“The IMD’s report is almost ready. We will implement it (new normal dates) from this year. It will not be changed for Kerala. But for other places, it’ll be changed. It’ll arrive early at few places and late at other places. Mostly, it’ll be late in central India. There will, however, not be a drastic change in arrival dates,” said Madhavan Rajeevan, secretary, ministry of earth sciences (MoES).
The central India comprises 10 IMD’s sub-divisions — Chhattisgarh, Odisha, west Madhya Pradesh, east Madhya Pradesh, Vidarbha, central Maharashtra, Konkan and Goa, Gujarat region and Kutch and Saurashtra.
Rajeevan, speaking on sidelines of the IMD’s 145th foundation day function here on Wednesday, noted that the marked change may be noticed in the ‘normal’ withdrawal date of monsoon from north-west India. “It’ll be 10 days late,” he said.
Last year, the withdrawal of monsoon was commenced on October 9 which was historically the most delayed withdrawal against the normal withdrawal date of September 1. Before 2019, the most delayed withdrawal was recorded in 1961 (October 1) followed by in 2007 (September 30).
The MoES secretary, however, did not specify whether climate change was behind the IMD’s move to change the ‘normal’ dates. He said the weather agency had noticed the changes in rainfall patterns over the year but did not revise the dates.
“It may not be climate change. It must be some systemic changes. I insisted that it should be brought out. We should not continue with the some 1940s terminology (references) to inform people about the monsoon rainfall,” said Rajeevan.
The upcoming changes will be the second such move by the IMD to bring a new benchmark as far as summer monsoon is concerned. Last year, the country could get a new benchmark that categorises ‘status’ of its summer monsoon based on the amount of rains it gets compared to the ‘normal’ rainfall during June-September period.
This ‘normal’, derived as long period average (LPA) of 50 years, had been revised downward from 89 cm to 88 cm, reflecting decline in average rainfall in India.
Rajeevan said the IMD was also working on to predict “impact based forecast” in case of rainfall like what it did in the case of cyclone prediction where it even advised what the authorities were expected to do to minimise its impact.
Citing example of Uttarakhand floods of 2013, the MoES secretary said the IMD was satisfied with its prediction of heavy rainfall but it could not tell the authorities about its likely impact.
“Impact of heavy rainfall could be different for different cities or regions, depending on ground situation. Therefore, it is important to come out with an impact based forecast in case of heavy rainfalls or any other weather events,” said Rajeevan.





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