Normal monsoon vs good monsoon

Vinson Kurian | Updated on: Apr 18, 2022
IMD gives only a 40 per cent chance for a normal monsoon this year while Skymet hints at 65 per cent probability

IMD gives only a 40 per cent chance for a normal monsoon this year while Skymet hints at 65 per cent probability

A ‘good’ monsoon ensures equitable distribution of rainfall across time and space

Will India have a good monsoon this year?

A ‘normal’ monsoon need not be a ‘good’ monsoon if it doesn’t ensure equitable distribution of rainfall across time and space. This is a tough call to take given that the seasonal weather system runs into a series of ‘scares’ while traversing the vast ocean waters or scampering over land.

So, April forecast probabilities vis-a-vis climatological probabilities (climatological statistics for a region rather than the dynamical implications of current conditions) tend to diverge a bit.

IMD gives only a 40 per cent chance for a normal monsoon while Skymet hints at 65 per cent probability. Above-normal (104-110 per cent of Long Period Average or LPA), below-normal (90-96 per cent of LPA), deficient (90 per cent of LPA or lower) or excess monsoon (110 per cent or above) assessments too vary, though not entirely out of tune with those made during the same time in 2019, 2020 or 2021.

If the probability of a good monsoon is just 40 per cent, why is IMD calling it a normal monsoon?

The probability of a ‘normal’ monsoon in April forecasts has ranged from 39 per cent in 2019 (season ended above-normal at 110 per cent); 41 per cent in 2020 (above-normal, 109 per cent ) to 40 per cent in 2021 (99 per cent). For 2022, the IMD has projected 40 per cent against the 65 per cent by Skymet. There is a valid case for expecting a normal monsoon this year, going purely by statistics.

Probability for a below-normal monsoon is at 26 per cent and deficient monsoon at 14 per cent this year (32 per cent and 17 per cent in 2019; 20 per cent and 9 per cent in 2020; and 25 per cent and 14 per cent in 2021). Two externalities with disproportionate influence on the monsoon are the La Nina in the East Equatorial Pacific and closer-home cousin Indian Ocean Dipole (IOD). While the IMD expects current La Nina to run through the monsoon, the IOD might turn to an unfriendly negative mode. The La Nina may not be as supportive this year and the IOD may turn tail, generating slightly elevated chances of an indifferent monsoon.

When was the last time India had so many years of good monsoon continuously?

The last time the country had three consecutive years of normal monsoon was between 1996 and 1998. Interestingly, the last time IMD had predicted a ‘below-normal’ monsoon was in 2015 when it projected a rainfall deficit of 12 per cent while the actual deficit came in at an enhanced 14 per cent.

It is not as if it pours every single day of the four-month (June-September) season. Dry interludes are embedded into the system. What should be cause for worry is the duration, extent and intensity of the dry spell.

Which parts of India will get normal rains and which parts will not?

The spatial distribution suggests normal to above-normal seasonal rainfall over many areas of northern parts of Peninsular India and adjoining Central India. Below-normal rainfall is likely over many areas of North-East India, some areas of North-West India and southern parts of the South Peninsula.

Will any part of the country get excess rains?

Excess rain is likely over South Gujarat, South-West Maharashtra, Rayalaseema, South-West Madhya Pradesh, Uttarakhand, parts of Central Uttar Pradesh and the foothills. Probability of excess rain for the country as a whole is only 5 per cent as per IMD forecast and practically nil, according to Skymet Weather (climatologically 17 per cent). In comparison, IMD had given a 2 per cent chance in 2019, 9 per cent in 2020, and 5 per cent in 2021. But the monsoon delivered 110 per cent, 109 per cent and 99 per cent, respectively.

Published on April 18, 2022
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