India Meteorological Department (IMD) has ‘Normal’ monsoon forecast for this year, or 99% of the long period average (LPA) of 87 cm. IMD has a multi-level monsoon forecasting system. Forecasts for April usually contain little detail about how much rain is expected during each of the monsoon months, and whether the rain will be one-sided or geographically distributed. The IMD usually shares it in late May or early June, right around the time when the monsoon is imminent in Kerala. Thus the forecast in April is only a general indicator and of little public utility. A normal monsoon forecast this year is also based on the absence of El Nio, which is linked to the drying up of monsoon rains. However, another ocean parameter called the Indian Ocean Dipole, whose positive phase is associated with good rainfall, has also been predicted to be ‘neutral’ or unsuitable for monsoon.
Another important piece of information has been made public. The IMD has changed its definition of LPA, which is an indication of average rainfall over a span of 50 years and must be updated every 10 years, as per norms of the World Meteorological Organization, of which India is a signatory. For myriad reasons, the IMD stuck with an LPA number of 89 cm (average monsoon rainfall from 1951-2000) until 2018, when it was updated to 88 cm (to reflect the average from 1961-2010). And now, to calculate the interval 1971-2020, the number is 87 cm. While on the surface, it may seem that India is losing just one centimeter of rainfall every decade, it should be remembered that this hides the wide variation in rainfall when calculated at the state and district levels because monsoon rains are highly uneven. . The IMD interprets the loss of one centimeter every decade as part of the natural cycle of the monsoon where 30 years of less rainfall, or a ‘dry’ era, is followed by a 30-year ‘wet era’. India ushered in a dry era in the 1970s-80s, says IMD; It is now in a neutral phase and will enter a humid era in the 2030s–2040s. The IMD has presented research over the years documenting changes in weather and precipitation down to the sub-district level, and states that global warming certainly has a role to play in its tendency to warm the oceans. Like the update of averages, the IMD should update some procedures and instead of maintaining the chronological conventions of long-range forecasts, a month or a fortnight ahead, emphasize shorter forecasts that are neither accurate nor useful. Huh.