IMD: This year’s monsoon is expected to be ‘normal,’ or 99 percent of the Long Period Average (LPA) of 87 cm, according to the India Meteorological Department (IMD). A multi-stage monsoon forecast system is used by the IMD. The April forecast usually provides little information about how much rain will fall during each of the monsoon months, as well as whether the rain will be asymmetrical or evenly distributed over the country. The IMD normally publishes this in late May or early June, right before the monsoon arrives in Kerala. As a result, the April forecast is simply a generic signal with the limited public utility.
The absence of an El Nio, a warming of the Central Pacific connected to the drying up of monsoon rainfall, is also expected to result in a normal monsoon this year. However, another ocean indicator known as the Indian Ocean Dipole, whose positive phase is linked to strong rainfall, is expected to be ‘neutral’ or unfavorable for the monsoon.
Another major piece of information has also been made public. The IMD has modified the definition of the LPA, which is a measure of average rainfall over a 50-year period and should be updated every 10 years, according to World Meteorological Organization standards to which India is a signatory.
IMD used an LPA of 89 cm
The IMD used an LPA of 89 cm (average monsoon rain from 1951 to 2000) until 2018 when it was modified to 88 cm for a variety of reasons (to reflect the average from 1961-to 2010). Now, to count for the period 1971-2020, the figure is 87 cm. While it may appear on the surface that India is losing only a centimeter of rainfall every decade, it must be remembered that because monsoon rain is so unequal, this masks large shifts in rainfall when computed at the State and district levels.
The loss of a centimeter every decade is explained by the IMD as part of a natural monsoon cycle in which 30 years of less rain, or a ‘dry’ epoch, is followed by 30 years of rain, or a ‘wet’ epoch. According to the IMD, India entered a dry period in the 1970s-80s is now in a neutral phase and will enter a wet epoch in the 2030-2040 decade.
The IMD has provided evidence over the years documenting recent changes in weather and rainfall down to sub-district levels and has stated that global warming, with its inclination to heat the waters, has undoubtedly played a role. Similar to the average update, the IMD must modernize some processes and place a greater emphasis on shorter forecasts, such as a month or a fortnight ahead, rather than sticking to antiquated long-range forecasting traditions that are neither accurate nor useful.