In charts: How has IMD’s monsoon outlook fared against reality?
IMD predicts one of the earliest monsoon arrivals in seven years with above-normal rainfall for 2025. On the other hand, private forecaster Skymet offers a slightly different outlook for the 2025 monsoon.
As scorching summer heat grips India, a welcome relief emerges on the horizon: the southwest monsoon has made its earliest entrance in seven years, arriving over parts of the Andaman Sea, the Bay of Bengal, and the Nicobar Islands.
India’s official weather agency, the India Meteorological Department (IMD), predicts that monsoon will reach India’s mainland by 27 May, five days ahead of the normal 1 June onset date.
Also read: Southwest monsoon rolls into Andaman and Nicobar region, two days in advance
According to IMD's 1961-2019 data, monsoons typically emerge on the Kerala coast around 1 June (with a standard deviation of about 7 days), making it the official onset date. From this point, the monsoon expands to cover the entire country by July before retreating by September, thus defining the official June-September monsoon season – the country’s rainiest period.
Historically, the monsoon has arrived before this date only four times in the past decade. If current forecasts hold, 2025's monsoon onset date will be among the earliest since 2009, when it began on 23 May. As these predictions are made with a possible error of four days on either side of the forecast onset date, IMD’s track record on monsoon arrival has been reliable.
Over the past decade, only 2015 saw a significant forecasting failure when monsoon arrived six days later than projected.
However, IMD's performance on overall monsoon rainfall predictions shows greater inconsistency. Since 2001, rainfall predictions have fallen within the acceptable error margin of 5% only eight times: in 2005, 2008, 2010, 2011, 2017, 2021, 2023, and 2024. Two-thirds of forecasts during this period have missed their model estimation, though accuracy has slightly improved over the last five years.
While IMD predicts above-normal rainfall for 2025 at 105% of the long-period average (LPA), private forecaster Skymet offers a softer outlook at 103% of LPA with a 5% error margin.
Also read: Mint Primer | A good monsoon will be great for India. Here’s why
The agencies differ on probabilities: Skymet forecasts a 40% probability for "normal" rainfall with only 30% chance for "above normal," while IMD projects 33% likelihood of "above normal," 30% "normal," and 26% chance of "excess" rainfall.
This divergence echoes 2024's pattern, when actual rainfall exceeded both organizations' forecasts. Both agencies have generally made accurate predictions that are well within the probable margin error, with 2022 being an exception where both underestimated rainfall levels. Skymet also slightly underestimated the 2024 monsoon rainfall.
The southwest monsoon, delivering 70-90% of India's annual rainfall between June and September, carries significant economic implications. Analysis shows that agricultural gross value added (GVA) has been robust during years with "normal" or "above normal" rainfall, typically growing 4-6% in such periods.
Whether normal or above normal, adequate rainfall generally boosts agricultural productivity, reduces groundwater dependence, increases rural incomes, and drives demand throughout India's economy. Conversely, below-normal rainfall, as seen in 2023's 6% deficit, can lead to price increases for essential commodities and export restrictions on foodgrains.
Also read: Early monsoon in India sparks hopes for bumper harvests, easing inflation
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