The south-west monsoon, which provides about 80 per cent of the rainfall that India receives annually, sets the pace for the country's economy. Shortfalls in the monsoon not merely affect agriculture but set off reverberations in other sectors too. There will, therefore, be relief all round that the India Meteorological Department (IMD) has, in its seasonal forecast issued on Tuesday, predicted that this year's monsoon is “most likely to be normal.” The IMD has used a statistical model to predict the probabilities for the monsoon falling in one of five categories: deficient (where the total nationwide rainfall is less than 90 per cent of the long-period average); below normal (from 90 per cent to 96 per cent); normal (96 per cent to 104 per cent); above normal (104 per cent to 110 per cent); and excess (above 110 per cent). The ‘normal' as defined in the IMD's probabilistic forecast is very different from the normal in the vocabulary of atmospheric scientists. In the latter case, it refers to a monsoon when the rainfall is between 90 per cent and 110 per cent of the long-period average. However, when the probabilities for the middle three categories are added, the chances of a ‘normal' monsoon (in the sense used by scientists) will work out to 93 per cent. The rainfall data for over a century show that such a ‘normal' monsoon occurs in seven out of ten years. In other words, there is a greatly heightened probability of the monsoon turning out to be normal this year. By the same token, the prospect of a deficient monsoon, which always arouses the most concern, is put at just six per cent this year. That too is good news since such deficient monsoons have occurred in about 18 per cent of the years and, what is more worrying, on three occasions in the last 10 years. The chances of this year's monsoon turning excess are put at just one per cent.
The outlook for the monsoon can change in the coming months and this year's outcome is particularly difficult to forecast. Last year's monsoon was helped by a La Nina that began to develop in June, with the waters of the equatorial eastern and central Pacific Ocean turning cooler than usual. That La Nina has weakened. This transition phase is difficult to predict and the models are currently displaying a range of possibilities. A majority of the models suggest the present La Nina conditions could continue till June and then weaken further, according to the IMD. The question is whether this could set the stage for an El Nino to develop, with the equatorial Pacific becoming warmer than usual. An El Nino often adversely affects the monsoon and has been associated with 65 per cent of the drought years. Changes in the Indian Ocean too can have an impact. Let us hope that the IMD's prediction for a normal monsoon holds.