Monsoon dates to be revised

Met department says monsoon activity has shifted in the past 60 years  

By Dinsa Sachan
Last Updated: Thursday 17 September 2015

mapTHE India Meteorological Department (IMD) is set to revise the dates of monsoon onset and withdrawal over the country. Between 1941 and 2000, there has been a shift in monsoon activity, with arrival and withdrawal delayed by seven to 10 days.

Ajit Tyagi, director general of IMD in Delhi, made the announcement in the first week of October. It comes in wake of a report prepared by Tyagi and S D Attri, deputy director general meteorology (international) at IMD. It shows that maximum deviation from normal dates (average of dates of several years) was observed in the Andaman and Nicobar Islands, with showers arriving about seven to 11 days later than usual. The islands record the first monsoon rainfall in the country.

IMD, however, maintains that this is a slight change.

A B Mazumdar, deputy director general of IMD’s Pune branch, says the department recognises that the current set of dates needs to be updated. “IMD is collecting information about the onset and withdrawal dates over the past decade from stations all over the country. These will be verified against the report by Tyagi and Attri,” he says. After a careful analysis by experts, we will revise the dates, he adds. “But the changes are not likely to be significant.” IMD has not set a deadline for the analysis.

M Rajeevan, senior scientist at the National Atmospheric Research Laboratory in Tirupati, says, “It is about time the dates were revised. The current dates were calculated in the 1940s.” Asked if climate change was responsible for the shift in monsoon activity, Rajeevan says, “You cannot rule out climate change, but these changes are most likely natural. Monsoon has natural variability. Phenomenon like El Nino (abnormal warming of the Pacific Ocean) can also play a role in shifting monsoon dates.”

The revision of dates could have an impact on crop planting and groundwater. Gurdev Singh Hira, former additional director of research at Punjab Agricultural University, explains, “Officially, monsoon is supposed to arrive in Punjab around June 30. But farmers try to plant rice by mid-May and in the absence of rains they use groundwater. This leads to over extraction.” We have managed to push them to not plant the crop before June 20. If IMD delays the onset date, it will be difficult to convince the farmers to delay the sowing, he adds.

Jayashree Sengupta, development economist at the Delhi-based think-tank Observer Research Foundation, says the change will have a major influence on agriculture only if there is a difference of more than two to three weeks. Vinay Sehgal, senior scientist at the Indian Agricultural Research Institute in Delhi, concurs. “Onset and withdrawal dates are climatic parameters of monsoon which have inherent variability,” he says. Onset and withdrawal dates vary every year and farmers adjust accordingly, he adds.

The accuracy of monsoon prediction is an important factor, and this is where IMD needs to step up its efforts, Sengupta concludes.

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  • With reference to monsoon

    With reference to monsoon dates to be revised, here are some of my observations: Around 1972, with reference to a question raised in Parliament ‘Whether the present date of onset over Delhi (June 19) is correct?”. Daniel et al. (1972) prepared a report on the revision of dates of onset of the Southwest Monsoon over the West Coast and Delhi” was prepared and submitted to the government – myself & Mrs. Jayanthi were the co-authors of this report – we were not allowed to publish this in IMD Journal -- in fact I prepared the journal article, which is still with me. The revised date for Delhi was July 2nd. They were 31st May/June 1 for Kerala and 10th June for Mumbai. In this connection I collected the data of dates of onset and withdrawals from IMD IDWRs, WWRs and MWRs and compiled the data for all the sub-divisions [1921 to 1975] -- by which I got Asthma and now with fish medice in 1977 I got cure. Based on this data I revised the maps of dates of onset and withdrawal. This paper was not allowed to send to IMD journal for publication. A part, dates of onset over Kerala coast trend along with its relation to lower stratospheric winds was however allowed and it was published in 1977 -- all these are now available in my book “Dry-land Agriculture: An agroclimatological and Aro Meteorological Perspective"; BS Publications, Hyderabad, 2002. The onset dates show 52-year cycle and the same way Fortaleza rainfall around this latitude in Brazil also showed 52-year cycle. Dr. S. Jeevananda Reddy

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