1. Monsoon onset may be late, here’s why it may not matter

Monsoon onset may be late, here’s why it may not matter

There’s no correlation between when it hits Kerala and how much it rains, where.

By: | Updated: May 17, 2016 4:10 PM
monsoon There’s no correlation between when it hits Kerala and how much it rains, where. (Reuters)

For a country desperate for rains, the news probably couldn’t have been worse. The Met Department on Sunday said the monsoon, whose normal date of arrival is June 1, was likely to be late by a week, possibly more. It said the onset of the monsoon over the Kerala coast was now likely on June 7, with the possibility of it being four days early or late.

The onset over Kerala marks the start of the four-month monsoon season that brings more than 75% of India’s annual rainfall. India receives about 116 cm of rain every year, about 89 cm of which comes in the June-September period. Because it is seen as the harbinger of good news, the date of onset is tracked very keenly.

The Andaman and Nicobar Islands and Lakshadweep start getting monsoon rain around May 20, much before Kerala does, but it is the arrival on the Kerala coast that is considered significant, because it is only then that the monsoon winds start their northward journey over the rest of the country.

Important as it is, the date of arrival of the monsoon has only limited significance. It is a single event, because of which there is greater uncertainty about it happening on any given date. In fact, in the last five years, only once has the onset happened on June 1. Last year, the monsoon was declared as having arrived only on June 5.

Also, the arrival of the monsoon is not the same as Kerala receiving its first showers around the last week of May or the first week of June. Certain pre-defined criteria have to be fulfilled for the Met Department to announce that the onset has happened — and that the rest of the country can also start to expect rain in the following days. For the monsoon to be declared as having arrived, at least 60% of the meteorological stations in Kerala must record 2.5 mm or more of rain for two consecutive days. All rain that occurs before the onset is described as “pre-monsoon showers”.

The important thing to understand is that the date of arrival of the monsoon has no bearing on the amount of rainfall in the four-month season. Late arrival does not mean less rainfall, or vice versa. The Met Department’s Sunday prediction of the onset of the monsoon did not say anything about the forecast it made last month about the likely rainfall this season. That forecast — of 106% rain — remains unaltered.

In fact, in the last 60 years, there have been 10 occasions when the onset has happened after June 5. In 1983, it happened as late as June 13. Only 4 of those 10 years saw less than 96% of normal rainfall. In 2 of those years, rainfall was actually more than 100% of normal.

Late arrival over Kerala does not mean that the monsoon would be late over other parts of the country as well. The northward movement of the monsoon after hitting the Kerala coast depends largely on local factors like the creation of depressions or low pressure areas. Many a time, the progress of the monsoon is held up for days because the conditions to pull it northward do not exist. The spread of the monsoon has no correlation with its date of arrival.

A delayed monsoon, therefore, has significance only in the short term. The wait for the rains has got prolonged. Coming on the back of two successive years of deficient rainfall, and for a country facing extreme heat, drought, and a drinking water crisis in many regions, this is certainly a mood dampener. Especially since the upbeat forecast of 106% rain this season had made people look expectantly towards June.

The despair can quickly disappear once it does start to rain. If the Met forecast turns out to be true, the fact that the monsoon was delayed would be of trivial interest, if not entirely inconsequential.

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