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Slightly Delayed, But Normal: How Do We Know When Monsoon Has Arrived In India

Representational image.

Representational image.

Monsoon is tipped to hit Kerala on June 3 and this year it is expected to bring normal rainfall in India

The monsoon this year is predicted to hit Kerala two days later than the date of its usual arrival on the Indian mainland on June 1. The outlook though is for a normal rainy season across most parts of the country. So, how is the date fixed and what makes the monsoon so important for India?

How Is It Known When Monsoon Has Hit?

Earlier this month, the India Meteorological Department (IMD) and private weather agency Skymet gave divergent dates for the onset of the 2021 monsoon season. While IMD said that the monsoon is delayed by a few days, Skymet said it had already arrived. It wasn’t the first instance of a disagreement between the two on the subject.

IMD has a checklist for deciding when it can declare that the monsoon has hit. It is agreed that given its geographic location, the south-west monsoon first fetches up in Kerala before moving to the rest of the country. The first factor that IMD looks to before announcing that monsoon has arrived is, of course, rainfall.

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If 60% of 14 designated weather stations report 2.5mm or more rainfall for two consecutive days after May 10, “the onset of monsoon Kerala [can] be declared on the 2nd day", IMD says, adding that there are certain other criteria that have to match, too. These include the depth of westerly winds in the region and the radiation emitted from the Earth.

What Has Delayed The Monsoon This Year? How Often Does That Happen?

The forecast this year was initially for the monsoon to arrive on May 31, earlier than the normal date of June 1, but according to IMD, a cyclonic circulation along the Karnataka coast is halting its progress.

IMD has been “issuing operational forecasts" for monsoon’s onset over Kerala since 2005 onwards with an error margin of ±4 days. In the 16 years between 2005 and 2020, the weather department said, all its predictions have been correct except in 2015.

But late arrival does not mean the monsoons will be affected, or that there will be a knock-on impact that will delay rains in other parts of the country. In 2016, although monsoon arrived in Kerala on June 8, it had covered the entire country by July 13.

What Is A Normal Monsoon?

If rainfall during the south-west monsoon ranges between 96%-104% of the ‘Long Period Average’ (LPA), then it is considered to be a normal monsoon season. The LPA itself is the average data for rainfall recorded across India between 1961 and 2010, which is 88 centimetres.

The forecast is for a normal monsoon in 2021 with total rainfall between June and September in India “likely to be 101% of the LPA", give or take 4%. But regional variations are expected. Thus, rainfall is most likely to be normal over Northwest India (92%-108%) and the Southern Peninsula (93%-107%) but below normal for Northeast India (<95%). Central India (>106%) is tipped to have an above-normal monsoon season.

IMD said that most parts of the country are expected to receive “normal to above normal rainfall" and that is especially true of the rainfed agricultural regions where rainfall is tipped to above 106% of the LPA.

Why Is Monsoon So Crucial To India?

According to news agency Reuters, the monsoon is responsible for 70% of India’s annual rainfall and the fate of multiple crops across the country are inextricably linked to it, including important crops like rice, wheat, sugarcane, etc. Considering that agriculture contributes 15% of India’s $2+ trillion GDP and employs more than half of its labour force, a bad monsoon is bad news for the people and the markets.

Sufficient and timely monsoon rain has the effect of boosting farm yields, putting more money in the hands of farmers, which in turn can lead to an uptick in rural demand.

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first published:June 01, 2021, 14:45 IST