IMD forecast ‘normal’ monsoon, updates definition of ‘average’ rain

The country had received normal rainfall during the four-month southwest monsoon season in 2019, 2020 and 2021

The country had received normal rainfall during the four-month southwest monsoon season in 2019, 2020 and 2021

The India Meteorological Department (IMD) while forecasting a ‘normal’ monsoon for this also revised downwards the definition of what constitutes average rainfall as part of periodic update. India, the agency said at a press briefing on Thursday, would get 99% of the Long Period Average (LPA). The LPA was 89 cm until 2018and was changed to 88 cm that year. In 2022, this has been again updated to 87 cm.

A monsoon is considered ‘normal’ when it falls between 96%-104% of the LPA.

The definition of the LPA, said M Mohapatra, Director General, IMD, is meant to be updated every decade. The 89 cm average was computed based on a 50-year average from 1951-2000, the 88 cm based on 1961-2010 and the latest based 1971-2020. When seen over a century, the average rainfall changes every decade with roughly thirty years of a declining trend followed by thirty years of an upswing, said Mohapatra. “Currently India is at the end of a dry epoch and we seem to be entering a wet epoch. The next update will be after a decade.”

Weather station data historically used to be delayed but now the IMD had moved to an automated system that provided real time data from close to 5,000 stations compared to the 1,000-odd from even a decade ago. “We have now updated all of this and therefore are able to provide these updated numbers (of LPA),” he added.

Current indications suggest ‘normal’ to ‘above normal’ seasonal rainfall in northern parts of peninsular India, Central India and the Himalayan foothills a. Many parts of Northeast India and southern parts of South India are expected to see subdued monsoons.

The IMD doesn’t expect an El Nino, a phenomenon associated with a warming of the Central Pacific and drying up rains over northwest India, to form during the monsoon months. “Currently La Nina conditions are prevailing over equatorial Pacific. The latest forecasts indicates it will continue during the monsoon.”

The IMD’s April forecast doesn’t indicate if some monsoon months will experience below normal rains, or regional variations. This information is expected by May-end.

On Tuesday, private weather forecasting agency, Skymet, too forecast monsoon 2022 to be ‘normal’ adding that rainfall in August, the second rainiest month, will likely be subdued.

Among the consequences of climate change are alterations to the monsoon. There are increased stretches of dry spells followed by spells of intense rain. However officials says that while the monsoon patterns are affected, monsoon rains are expected to increase over the next decade. “External forces, especially from the oceans impact the monsoon and these are being studied. But the thirty year pattern is expected to hold and the next revision might see an increase in the decadal average,” said M Ravichandran, Secretary, Ministry of Earth Sciences.

As part of its update, the IMD said that annual rainfall had decreased to 116 cm from 117.6 cm. Southwest monsoon contributes about 75% of India’s total rainfall with June (19%), July (32.3%), August (29.4%) and September contributing 19.3% respectively.

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