IMD to release forecast on monsoon; Know how many times predictions were accurate

It's often joked that predicting weather is the second most difficult problem and the first being predicting human behaviour, but the Indian Meteorological Department is making huge efforts and investments to keep us updated about the upcoming weather and its impact.

Like every year, the IMD is all set to release its final report on the southwest monsoon forecast, and that will reveal if El Nino will have any impact on the June-September rains, causing low rainfall.

According to Skymet Weather, which is a private forecasting agency, this year Inida is likely to witness below-normal monsoon rainfall, with a 20 percent chance of drought due to the end of La Nino weather situation, but IMD's LRF is still awaited that will clarify the upcoming season.

El Nino? How can it affect the monsoon in India?

El Nino is a weather condition that is responsible for the warming of the waters in the Pacific Ocean near South America. El Nino can affect the monsoon winds and cause less rainfall in India. In more simple terms, it is the "warm phase" of a larger phenomenon that has an impact on ocean temperatures and the speed and strength of ocean currents.

This year, the India Meterological Department has forecast a normal monsoon, with rainfall pegged at 99% of the long-period average (LPA). Let's have a look at the IMD's past predictions and how accurate they were.

Past record of IMD's weather forecasts; Know how accurate they were

Based on past data, it can be said that IMD's monsoon predictions have mostly been accurate. Also, the agency's long-range forecasting skills are improving. Every year, IMD's long-range forecasts (LRFs) of the monsoon are made in the month of April, and they carry a 5% point margin of error (plus or minus). Last year, the agency's long-range forecast of 98% seasonal rainfall was accurate, as the monsoon ended up at 99% of the Low Pressure Area. However, such accuracy was not recorded often, as eight out of ten times in the past decade IMD's forecasts' were outside the margin of error. Notably, the two times when the forecasts came true were back in 2011 and 2017.

What was the deviation? When did it falled out of error margin? The average deviation of IMD's forecasts between 2011 and 2020 was 7.1 percentage points, which is higher than the error margin of the forecasts. However, this forecast was an improvement from the previous decade (between 2001 and 2010), when IMD's monsoon predictions varied from actuals by 8.6 percentage points on average. It is pertinent to mention that the quantitative forecast of seasonal rainfall is a notoriously complex task that no other national weather agency undertakes. IMD started quantitative forecasts in the late 1980s.

Image: PTI