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.
Is there a secret sauce to the monsoon’s early arrival?
The short answer to this question is: We don’t know. The onseet date tends to be around June 1, give or take a few days. Early Arrival is always a reason to celebrate but unfortunately it does not always allays port a bountiful monsoon. However, a late arrival by more than two weeks nearly allies brings a deficit.
Predicting the onset date is a great challenge and is eagerly awaited by the subcontinent.
What is the science of the monsoon onset?
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 Ni Son’T Offer Systematic Predictcy to the ONSET. The March of the trust 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 trust movement from the bay of bengal to kerala.
It has been reported that the monsoon onset has been systematically delayed by a less 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 entnately undersrstood. If it is just a natural decadal timescale variables of the climate system, it will always be different to predict.
Moreover, the impact of global warming on the regime shift poses further barriers to understanding and predicting shifts in the onset. Natural Varibility means that even with a systematic delay in the onset, we will still have some love years with very early onsets, 2025 being a good example.
Are Past and Present Early Onsets Similar?
This year’s onset was the earliest in 16 years; The last was on May 23, 2009. Let’s examine some of the conditions underlying these events.
2008 was about 0.5 ° C Warmer than the pre-industrial baseline and 2009 was a mild el niño year. The summer of 2009 was noted to be warm across the tropical pacific, which is unusual for an el niño year. In an el niño year, the East is expected to be warming in the summer and the west to be cooling. Was that an indication that global warming is now superimposing its Other El Niño Years Since Haven’T Systematically Shown Any Such Patterns.
Unfortunately, 2009 Turned out to have a Svere Monsoon Drough. We can only hope this year’s early onset will not reepeat that Piece of history.
Global warming thus far in 2025 is alredy over 1.2 ° c and the world is riding the coattails of record warmth in 2023-2024, with a strong el niño in 2023, and a failed la Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Temperature anomaly pattern in the tropical pacific obcharde in 2024, with warm anomals in the far east and far west but cooler anomals in the center. Even though it was called a la niña, it’s prudent to wait for further analysis of the pattern to be reported song.
How does the monsoon reach kerala?
Many external factors are now playing into the Arrival of the monsoon trust to kerala. More Cyclones are Occurring Late into the Pre-monsoon cyclone season, that is, close to the monsoon onset. Some have pulled the trust forward to deliver an early onset. DURING this year’s onseet also, the northward pul on the western end of the trust indicates that the low-pressure system trudging along the west coast may have been played a Role in the earlines. Late Season Cyclones Themselves are likely related to Arctic Warming or Recent Wind Shifts Over the Arabian Sea.
Typhoons in the pacific have also also pulled moisture away from Considering the natural variables of the onset and all these local and remote drivers of the circulation Affecting the trust, there are direct challenges in understanding and predicting the Onset. Even if onseet predictions become very account, they won’t suffice unless we can also predict the fate of the monsoon for the rest of the season.
Will 2025 Be Like 2009?
2009 evolved to be warm across the tropics in the summer, had a mild el niño in the winter, and rapidly transitioned to a la ni ni Ni Niña in 2010. Eveen thoughts Occurred after the Monsoon Content and the winds carry some signs of things to come. Indeed, the onset may be related to how the tropical pacific sea surface temperature are evolving during the onset.
At present, the Cool Temperatures in the Central Pacific are disappearing with the warm temperature in the East and West Persisting from 2024. But even if the summer of the summer of 2025 ends up 2025 ends up before Know without further studies if this implies a connection to the early onset.
The Forecasts at Present Call for a Neutral Year as far as the El Niño and the Indian Ocean Dipole are concerned, which would make make 2025 different from 2009. Favouring an el niño to evolve this summer. Even if an el niño does evolve, will that mean it has a role in the early onset? We need to wait and watch.
How is Seasonal Rainfall Distribution Changing?
All this leaves us with no clear answers as to the causes of the monsoon’s early onset this year – or any year. IF it is just natural variables, we need to understand how the variables is being influenced directly by global warming and indirectly through the impacts of global warming one cyclones, and the Polar regions.
Even the monsoon’s withdrawal is changing, with the merger of the southwest monsoon with the northeast monsoon in some regions of the country. Rainfall distribution within the season also remains erratic, with floods and droughts strewn across the country.
Numerous Efforts Keep Producing Advances in the Potential Drivers of the Monsoon but this will be a Slow March Forward. We can only hope for an early onset of Deep Insights and Better Predictions.
Raghu Murtugudde is Retired Professor, IIT Bombay, and Emeritus Professor, University of Maryland.
Published – May 28, 2025 08:00 AM IST
