Why has the monsoon come early this year? | Explained Premium

Unraveling the complexities of the Indian monsoon onset and its connection to global warming remains a challenging mystery.

The story so far:

Last week, the India Meteorological Department said the southwest monsoon set in over Kerala on May 24, a week ahead of its normal onset. Since 1975, the earliest monsoon onset over Kerala occurred on May 19, 1990, 13 days ahead of schedule.

The short answer to this question is: we don’t know. The onset date tends to be around June 1, give or take a few days. Early arrival is always a reason to celebrate but unfortunately it doesn’t always portend a bountiful monsoon. However, a late arrival by more than two weeks nearly always brings a deficit.

Predicting the onset date is a great challenge and is eagerly awaited by the subcontinent.

There are many theories as to the science of the onset. But this just means there is no consensus on a complete understanding of the processes leading to the onset. Even the famed El Niño and La Niña don’t offer systematic predictability to the onset. The march of the trough is watched carefully from its origin in the northwestern tropical Pacific into the Andaman Sea and the Bay of Bengal. But many players still tinker with the trough movement from the Bay of Bengal to Kerala.

It has been reported that the monsoon onset has been systematically delayed by a few days since the 1970s. There have been many studies of a regime shift in the climate system as well as the ecosystems around the time but the shift’s causes are not entirely understood. If it is just a natural decadal timescale variability of the climate system, it will always be difficult to predict.

Moreover, the impact of global warming on the regime shift poses further barriers to understanding and predicting shifts in the onset. Natural variability means that even with a systematic delay in the onset, we will still have some years with very early onsets, 2025 being a good example.