The India Meteorological Department (IMD) has forecast a ‘normal’ monsoon for this year, or 99% of the Long Period Average (LPA) of 87 cm. The IMD has a multi-stage monsoon forecast system. The April forecast usually has little detail on how much rain is expected during each of the monsoon months, and whether the rain will be lopsided or evenly distributed geographically. The IMD usually shares this in late May or early June, just around the time the monsoon is imminent over Kerala. The forecast in April is thus only a general indicator and of little public utility. A normal monsoon forecast this year is also predicated on the absence of an El Niño, a warming of the Central Pacific linked to the drying up of monsoon rains. However, another ocean parameter called the Indian Ocean Dipole, the positive phase of which is associated with good rains, has also been forecast to be ‘neutral’ or unhelpful for the monsoon.
There has also been another significant bit of information made public. The IMD has changed its definition of the LPA, which is an indication of the average rainfall over a 50-year interval and, as per the norms of the World Meteorological Organization to which India is a signatory, should be updated every 10 years. For myriad reasons, the IMD stuck with an LPA number of 89 cm (the average monsoon rain from 1951-2000) until 2018, when it was updated to 88 cm (to reflect the average from 1961-2010). And now, to count for the 1971-2020 interval, the number is 87 cm. While on the surface, it might look like India is losing just a centimetre of rainfall every decade, it must be remembered that this conceals wide shifts in rainfall when computed at the State and district levels as the monsoon rain is highly uneven. The IMD explains the loss of a centimetre every decade as part of a natural cycle of the monsoon where 30 years of less rain, or a ‘dry’ epoch, is followed by 30 years of a ‘wet epoch’. India began a dry epoch in the 1970-80 decade, the IMD says; it is now in a neutral phase and will enter a wet epoch in the decade, 2030-2040. The IMD has presented research over the years documenting the changes in the weather and rainfall in recent years down to sub-district levels, and has said that global warming, in its tendency to heat the oceans, has certainly had a role to play. Much like the update to the average, the IMD must update some processes and lay stress on shorter forecasts, a month or a fortnight ahead, rather than maintain anachronistic traditions of long-range forecasts that are neither accurate nor useful.