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IMD predicts excess rainfall

There is a 96 per cent chance that monsoon this year will be between normal and excess, said the IMD. Photo: S. Gopakumar  

Even while maintaining that the torrential rain in Kerala was pre-monsoon showers, the India Meteorological Department (IMD) on Thursday said in an update to its April monsoon forecast that rainfall would be 6% above the 50-year average of 89 cm.

Rains over north-west India would be 8% more; over Central and South India 13% more and over north-east India 6% less than what these regions historically got.

Monsoon during the months of July and August — the most critical for agriculture — are also expected to be munificent with the agency predicting rainfall monsoon to be 7% and 4% more than what the country usually gets during these months.

As The Hindu reported earlier, the IMD was increasingly confident about the probability of copious monsoon rains due to the receding of the dreaded El Nino — the anomalous heating of surface waters in the equatorial Pacific and six in ten times responsible for a drought — and several international weather agencies predicting that the converse La Nina conditions are likely to set in the latter part of the July-September monsoon season. The other factor from which the IMD derives confidence is that the monsoon has failed only once in a quarter century during a so-called La Nina year.

Floods likely

In fact, the country may have to brace for floods and the possibility of the monsoon spilling over into October. “There is a possibility of rains after September,” said Laxman Rathore, IMD Director-General.

“October is definitely going to see significant rain,” said Jatin Singh, CEO, Skymet, a private weather forecasting agency. The IMD maintained that the monsoon was yet to set in over Kerala and would do so “in the next three or four days”.

The receding of El Nino will increase rains.

What defines a monsoon?

The India Meteorological Department (IMD), the official weather agency, laid down a set of criteria in 2005 to define the monsoon onset in Kerala.

According to that, at least 8 of 14 meteorological stations Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kasargode and Mangalore ought to report rainfall of 2.5 mm or more for two consecutive days. Along with that there ought to be minimum range of wind speed and a characteristic heat waves called Outgoing Longwave Radiation as well as a steady pattern of the monsoon winds at specified height in the atmosphere. Only when all of this is satisfied for two days continuously does it count as monsoon.

To Madhavan Rajeevan, Secretary of the Ministry of Earth Sciences, the wind criteria was critical else it was quite possible that the Kerala rains could wither away.







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Printable version | May 9, 2021 10:45:22 PM | https://www.thehindu.com/news/national/IMD-predicts-excess-rainfall/article14380455.ece

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