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Informist, Tuesday, Sept. 16, 2025

 

 

By J. Navya Sruthi and Shreya Shetty

 

 

MUMBAI – Though the withdrawal of the southwest monsoon began three days ahead of its normal date, the complete withdrawal is likely to be delayed beyond the normal date of Oct. 15, said A. Suryachandra Rao, director, Indian Institute of Tropical Meteorology, Pune. According to studies conducted by the institute, the development of La Nina conditions over the Pacific Ocean usually delays the southwest monsoon current from pulling out of the country entirely before its normal date, he said.

 

 

The southwest monsoon usually begins withdrawing from the country around Sept. 17, and it withdraws from the entire country around Oct. 15. Multiple weather agencies across the globe, including the India Meteorological Department of India, see La Nina conditions developing briefly in the last three months of the calendar year 2025. El Nino is linked to drier, hotter weather in India, while La Nina results in more favourable rainfall.

 

On other hand, negative Indian Ocean Dipole conditions have already developed, Rao said. A negative Indian Ocean Dipole leads to less rainfall in India, while a positive index leads to more rainfall. However, between a negative Indian Ocean Dipole and La Nina, the latter is the more dominating weather phenomenon, he said. As such, a negative index is not expected to affect the intensity and spread of rainfall over India during September, he said. The negative index is likely to favour better rainfall during northeast monsoon, he added.

 

The following are edited excerpts from the interview:

 

Q. Monsoon began withdrawing on Sunday, three days ahead of the normal. When is the withdrawal expected to complete? Should we anticipate any break in withdrawal, just like what happened during the onset of the monsoon?

A. This time also the withdrawal throughout the country will be a little delayed. So, some parts may be seeing faster withdrawal progression, but in the country, it will be little delayed because you have La Nina conditions developed in the Pacific. As per studies (when it comes to withdrawal of monsoon) we normally look at central India, the monsoon core region. So, we expect a delay there. It is very difficult to quantify the number of days. So, we know that in recent times, the delay was almost plus or minus 10 days.

 

Q. There is a negative Indian Ocean Dipole currently. Will this affect the withdrawal of southwest monsoon and the onset of the northeast monsoon?

A. Whenever you have a strong La Nina in the tropical Pacific, we also get negative dipole in the Indian Ocean. So, if you look at these two conditions, what happens is that they favour (southwest monsoon). Mostly, La Nina is the dominating feature. So, whenever a negative dipole is there, we normally expect below normal monsoon rainfall. But when it comes to late parts of monsoon like September and October, it somehow tends to delay the withdrawal.

 

Q. How do you see rainfall in September? Will it be below normal at the end of this month because of negative Indian Ocean Dipole or above normal?

A. Negative dipole can decrease it, but at the same time we have a competing phenomenon in the tropical Pacific, which is taking over (negative dipole). La Nina is dominating; therefore, we should expect above normal rainfall.

 

Q. The current La Nina conditions in tropical Pacific and negative Indian Ocean Dipole, are these going to impact the northeast monsoon?

A. Studies are not much well documented because northeast monsoon is only restricted to very few states. Actually, one state, mostly Tamil Nadu. We do not have a clear signal about what happens to northeast monsoon. But when you have a negative dipole, you get better rainfall (during northeast monsoon).

 

Q. Research papers by the IMD suggest that the duration of the southwest monsoon has been increasing by 1.6 days every year. What is your view on this? And if it is true, what could be the reason behind the same?

A. I do agree with their studies. Whenever we have La Nina-like conditions in the tropical Pacific, withdrawal is always delayed. Therefore, the length of the rainy season will increase. Also, we all know that there was a hiatus, until recently. So during that time also, we have a strong cold pole in the tropical Pacific, which is same thing as La Nina, but lasted for a long time. Therefore, I fully agree with their study that the length of the rainy season has been increasing in recent times.

 

And if you look at reality, there is always a decadal signals. Some decades, it actually works very stronger and some decades, it does not work strong. For example, in the late 1970s and early 1980s, the relation was not very good. Then, we  did not see any connection between Pacific La Nina and withdrawal of monsoon.

 

Q. What would be the effect of this delay in withdrawal of monsoon on the agriculture sector? Do you think it is time for our farmers to shift from those traditional crops to some other varieties?

A. Research farms, because of a lot of rainfall, have moisture stress or more water stress. So the yield may decrease. But in the reality, what happens is that there are several crops which can withstand floods for some time. That way the yield may increase. But at the same time, if you are going only with the typical or traditional seeds, which are not genetically modified, then their tolerance for these conditions is very weak and may definitely decrease the yield.

 

Q. Is the Indian monsoon currently going through a dry epochal phase? Can you elaborate on what that means, and when can we expect the country to enter a wet epochal phase?

A. The monsoon has a very large variability. It varies within a season. It varies within a year. And it varies within a decade. So when will a particular epoch end, to tell something like that is very difficult. I do not think science has come up to that stage. Only once we are in that epoch, we will understand that this is the epoch that is happening. And once it is developing, then we will understand that it will last for some time.

 

Particularly in central India we have a dry epoch. So, everywhere else monsoon rainfall is increasing or remaining same. But that decrease also will not last forever. As I said, there is a natural variability on its own. It does not have to be anything to do with climate change or anthropogenic. The variability we think is much stronger than any of these other forces. Of course, there will be some impact because of anthropogenic. But the signals coming from nature itself are much stronger.

 

Q. Do you think the agricultural sector players are factoring in these weather changes into their R&D process?

A. Yes, they are much more (involved in research and development), because that is the most important part of our life, you have to have food. They are developing a lot of different varieties of crops which are resilient to climate change. They have already done good work. Otherwise, our production would have been harmed a lot because of these extremes, but instead it is increasing day by day.

 

Q. The climate pattern in major cities in India has been changing due to a dense population over the years. Do you think cities are developing a climate structure of their own? If so, how prepared are cities to brace for the same?

A. Urban areas have their own climate, as you rightly mentioned. What happens is that when we build skyscrapers, it changes the atmosphere. There is something called the urban heat islands. When there is a cluster of buildings, there is more heat generated from that.

 

So definitely urbanisation will change the climate within that area. To address these problems and to understand how it is modifying the climate, we have these projects called urban meteorology project. We are starting it in Delhi, Chennai, and Vishakhapatnam. In Mumbai we already have it.

 

Q. Is the infrastructure in cities developing in accordance to climate change?

A. Infrastructure is developing very fast in urban areas. Things are much more organised than they were 10–20 years back.  Previously, during such (rainy) days, the whole of Mumbai used to be stagnant for several days. Now it is not the same. As you can see, it lasts for only one or two days. The infrastructure is also developing along with it. Everybody is preparing themselves for the changes that are happening.

 

Q. How much has global warming impacted the earth's natural climate cycle, which changes every few centuries? Has global warming sped up the cycle or slowed it down?

A. It is not a linear relationship. A linear relationship would mean that because (global) warming is happening, these climate cycles will be impacted either positively or negatively.

 

This is a very complicated interaction. For example, if global warming is increasing, the number of El Nino events go up. So then if El Nino (events) are increasing, then monsoon rainfall should decrease, right? But since global warming is happening, again the waters in the Indian Ocean, surrounding the Indian land are very warm. Therefore, more convection will happen, and you will get more rainfall. These are very complicated. It is not a straight answer to any of these things.

 

Q. How long are we expecting the negative Indian Ocean Dipole event to last?

A. Once a negative dipole develops in the tropical Indian Ocean, it will last till December, unless there is some other phenomenon that comes and kills it. The normal period is that it starts in June and ends by December. This time it started a little late, but because there is strong warming in the Eastern Indian Ocean, it is expected to last up to December. After September, we do not expect much rainfall from the monsoon. So, it (negative Indian Ocean Dipole) will not impact the monsoon much now. It will impact the northeast monsoon.

 

Q. You had earlier said that the La Nina event will dominate this negative IOD event. So how will the negative Indian Ocean Dipole event be beneficial for the northeast monsoon when La Nina can dominate it?

A. You have to look at the scales (of the monsoon). The (southwest) monsoon is a very big phenomena, whereas northeast monsoon is restricted to very small region. So, for northeast monsoon local sea surface temperatures are much more important. See southwest monsoon is a very gigantic phenomena. So, to modulate that, you need another gigantic phenomena (such as the La Nina).

 

Q. In January, parts of northwest and northeast India receive winter rainfall. Do you think the negative Indian Ocean Dipole event will impact these winter rains?

A. There is no connection, as per present research (between winter rainfall and Indian Ocean Dipole event). So, we do not know exactly whether it will impact the rainfall in other regions, particularly weather systems such as western disturbances.  End

 

Edited by Akul Nishant Akhoury

 

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