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

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

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

The India Meteorological Service (IMD) While a ‘normal’ monsoon was previously forecast, the definition of what constitutes average rainfall was also revised downwards as part of the periodic update. India, the agency said at a news conference on Thursday, would receive 99% of the Long Period Average (LPA). The LPA was 89cm until 2018 and was changed to 88cm that year. In 2022 this has been adjusted again 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 intended to be updated every decade. The 89 cm average was calculated from a 50-year average from 1951-2000, the 88 cm from 1961-2010 and the latter from 1971-2020. Looking at more than a century, average rainfall changes every decade by about 30 years from a declining trend, followed by 30 years from a rebound, Mohapatra said. “At the moment India is at the end of a dry era and we seem to be entering a wet era. The next update will be in a decade.”

Weather station data had been delayed in the past, but now IMD had switched to an automated system that provided real-time data from nearly 5,000 stations, compared to 1,000 even a decade ago. “We have now updated all of this and can therefore provide these updated numbers (from LPA),” he added.

Current indications point to ‘normal’ to ‘above normal’ seasonal rainfall in the northern parts of peninsular India, central India and the Himalayan foothills. Moderate monsoons are expected in many parts of Northeast India and southern parts of South India.

The IMD does not expect an El Niño to form during the monsoon months, a phenomenon associated with a warming of the central Pacific Ocean and drying rains over northwest India. “Currently, conditions prevail in La Nina over the equatorial Pacific. The latest forecasts indicate that it will continue during the monsoon.”

The IMD’s forecast for April does not indicate whether some monsoon months will see less than normal rain or regional variations. This information is expected at the end of May.

On Tuesday, private weather forecasting agency Skymet also predicted that the monsoon 2022 will be ‘normal’, adding that rainfall in August, the second-rainiest month, is likely to be moderate.

One of the consequences of climate change is changes in monsoons. There are longer periods of dry spells, followed by periods of intense rain. However, officials say that although monsoon patterns are affected, monsoon rains are expected to increase over the next decade. “External forces, especially from the oceans, affect the monsoon and these are being studied. But the 30-year pattern is expected to continue and the next revision could see an increase in the 10-year average,” said M Ravichandran, secretary of the Earth Sciences Ministry.

As part of the update, IMD said annual rainfall had decreased from 117.6 cm to 116 cm. The southwest monsoon accounts for 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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