Which way is monsoon headed?

The Application Laboratory of Japanese national forecaster Jamstec has reiterated that this year could witness the rollout of an El Nino coupled with a positive Indian Ocean Dipole (IOD) phase.

These are two keenly watched near- and far-field climate phenomena thought to have a direct bearing on the performance of a concomitant Indian monsoon.

While El Nino signifies the abnormal warming of the Equatorial East Pacific, a positive IOD refers to a similar anomaly occurring in the western part of the Indian Ocean.

El Nino brings with it grim forebodings of likely drought-like conditions (though proved wrong on a few occasions) for the Indian monsoon, while a positive IOD signals reasonably good tidings.

“We may observe co-occurrence of a positive IOD and an El Nino in the latter half of 2017; this is just as in 1997 and 2015,” the forecast statement of the Japanese agency said.

In 1997, India had a normal monsoon year despite a strong El Nino. But, in 2015, the monsoon was in deficit since the positive IOD values were too low to alter the ambient weather over the country.

Because it evolves at a location closer to the India monsoon theatre, the IOD is thought to wield more influence on the seasonal rain pattern here than an El Nino brewing in the far-away Pacific.

This is what is mostly reflected in the latest forecasts by leading international models with respect to the playout of the June-to-September season in India. But, it is not as if a positive IOD phase can result in good rainfall uniformly across the landscape. It tends to favour Central India and the west coast with more rain than in other regions.

The Japanese agency as well as the European Centre for Medium-Range Weather Forecasts point to this probability and suspect that North-West India could suffer in the bargain with a rain deficit.

Jamstec picks out Chhattisgarh and Odisha in the East as also parts of the west coast as likely candidates for poor rain record during the season. Significantly, the rain deficits are predicted to occur during June-July-August, considered the most rainy months of the South-West monsoon season.

The European centre is of the view the rain deficit during June-July-August will be confined to North-West India (Rajasthan, Punjab, west Uttar Pradesh, Himachal Pradesh, Uttarakhand and Jammu & Kashmir).

The International Research Institute of Columbia University does not find any major deviation in seasonal rainfall for India except in March-April-May, when seasonal dryness would be marked most over Gujarat, west Madhya Pradesh and south-west and east Rajasthan.

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