How will the monsoon turn out? Not as well as previously thought appeared to be the answer when the India Meteorological Department (IMD) issued its updated seasonal forecast on Tuesday. Nevertheless, the data in the IMD's press release indicate that the most likely outcome is a ‘normal' monsoon, but one where nationwide rainfall during the season occurs at the lower end of the spectrum. Atmospheric scientists define a normal monsoon as one where the rain the country receives is between 90 per cent and 110 per cent of the long-period average. Rainfall data for over a century show that there is a 70 per cent chance that a monsoon will fall in this category. In the IMD's latest forecast based on a statistical model, the probability for that sort of normal monsoon works out to 80 per cent. So, although the probability for such an outcome has come down from the 93 per cent given in the forecast issued in April, the odds still favour another normal monsoon this year. However, the normal in the scientists' parlance is sub-divided into three in the IMD's classification: below normal (from 90 per cent to 96 per cent of the long-period average); normal (from 96 per cent to 104 per cent); and above normal (from 104 per cent to 110 per cent). The chances of a ‘below normal' monsoon have gone up from 30 per cent in the April forecast to 37 per cent in the latest prediction. The odds of a normal monsoon as defined by the IMD have fallen from 53 per cent to 37 per cent.
The possibility of a deficient monsoon — where rainfall is less than 90 per cent of the long-period average — has risen from 6 per cent in the April forecast to 19 per cent. Records of past years, however, show that a monsoon has an 18 per cent chance of falling in this category. There is, therefore, no significantly increased risk of this monsoon turning deficient. Nor are there warning signs from groups that use powerful dynamical models to simulate what happens in the oceans and the atmosphere that the current rainy season will fare badly. Although the La Nina, the cooling of the equatorial waters of the Pacific Ocean that aided last year's monsoon, has subsided, forecasters put a low probability on a warming that would lead to an El Nino, which could be detrimental to the monsoon. Unfavourable conditions in the Indian Ocean too have not been forecast. However, it is not enough for the monsoon to turn out to be normal; the distribution of rainfall too matters. The IMD's latest prediction indicates that rainfall in both July and August, which are important for agriculture, could be below par. Prolonged spells of little or no rain in those months would affect crops badly. Let us hope there won't be such breaks in the monsoon.
