Cloud atlas: Meet the met guy studying, and fretting over, how the Indian monsoon is changing
Madhavan Nair Rajeevan’s new book tracks shifts over 50 years, models we need to build. ‘We must find ways to track it; there’s too much at stake,’ he says.
Just as scientists around the world were beginning to understand the complex and mysterious Indian monsoon — one of the most powerful weather systems in the world — “we’ve been hit with climate change, which makes understanding it all the more complicated,” says Madhavan Nair Rajeevan, 63.
If there were ever a time for an updated reference book on the summer monsoon, he adds, it is now.
Rajeevan — who has been studying the monsoon for nearly 40 years, retired as secretary with the union ministry of earth sciences, and is currently vice-chancellor of Atria University, Bengaluru — has co-authored such a book, due out this month.
South Asian Summer Monsoon: Processes, Prediction, and Societal Impacts (written with Parthasarathi Mukhopadhyay, 60, a researcher at IITM, and Arindam Chakraborty, 50, a professor at the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science, Bengaluru) has been published by the Dutch academic banner Elsevier (which also publishes the journals Lancet, Cell and Science Direct).
The book draws on new science from the past five decades, picking up where Southwest Monsoon, written by meteorologist YP Rao in 1976, left off, and analyses more than 1,000 research papers, hypotheses, and climate models to offer an easy-to-access primer on current understandings of this monsoons system and how it is changing.
The idea was to keep the book simple enough for everyone to engage with, because the monsoon is something that affects us all, Rajeevan says.
Excerpts from an interview.
* What’s the most interesting thing you learnt, early on, about the monsoon?
That variability in rainfall within a day can be a result of the sun’s movements.
During the day, convection is higher (hot air rises; cool air rushes in to take its place). As surface temperature rises, air pressure drops, causing precipitation — and that’s one of the reasons hot and humid parts of India get more rain in the afternoons.
Lately, we have figured out the matter of decadal variability too. We have 30- to 40-year cycles of what are considered good and bad monsoons. These, it turns out, are driven by seasonal sea-surface temperatures in the Atlantic Ocean.
* You began to focus on the monsoon in 1994…
I initially worked on tropical cyclones and climate-change issues, when I joined the Indian Meteorological Department in 1986.
Then, in 1994, the long-range monsoon forecast failed. I was asked to work with the seasonal forecasting group to find ways to make such predictions more accurate.
By 2006, our group of researchers had created the daily rainfall data set that is still used today. It is a daily, 100-km-grid rainfall data set that consolidates raw data and missing data, and is accessible to anyone studying and researching weather patterns. In 2007, we also developed a statistical monsoon forecasting system. All this has helped make seasonal forecasting more reliable.
India now uses more-dynamic mathematical modelling systems too. But no prediction can be perfect. Because the internal mechanisms of the monsoon are still poorly understood.
It remains a complex mystery. And that is a handicap.
* How does it feel, to see this giant weather system altered as a result of human activity?
The monsoon is so important for our survival. It affects food, economy, health, energy, GDP.
We have studied it for decades, with the understanding that if we can predict, it will help us prepare. But now, climate change has added a new dimension to this variability, which we don’t yet understand.
While the basic principles of physics remain the same, the interactions between the physical systems — temperature, pressure, winds, clouds, etc — are changing because of global warming.
That can really complicate monsoon forecasting. It can keep us from understanding why certain things are happening. That is my main concern.
Our models indicate that the monsoon will intensify further in the near future. But so will the variability.
In one region there might be a drought, and in another there may be floods. This is already happening to a greater degree than it did before.
Will the models be able to pick this up and help us prepare, or not? That is the question.
* What can we expect in the immediate future?
We’ve always had a robust monsoon and will continue to have one. But data from the last 50 years shows increased intensity in bursts. This has led to more flash floods and landslides, in recent years.
The dry spells over the Indo-Gangetic plains have also increased. Earlier, they used to last eight to ten days. Now they stretch over 12 to 15 days. During this time, the Western Ghats also sees reduced rainfall.
Onset is occurring a week later in the plains. Once the monsoon gets there, there are now heavier rains and longer dry spells.
The total quantity of rainfall in a season will likely remain relatively unchanged in the near future. But how we receive that rainfall will continue to change.
* What will it take to better track the change?
We need to do a lot of modelling studies ourselves, and not just rely on and analyse the IPCC (Intergovernmental Panel on Climate Change) models.
We need to study the physical processes at a granular level, which is being done to a certain extent, but certainly not enough.
We need to study whether the El Nino-Indian monsoon relationship will change, and if so, what kind of relationship it will be.
Further, clouds still remain a cloudy issue in all existing mathematical models. We have not really understood how the clouds are going to behave — whether it’s current clouds or future clouds.
* You’ve said we need to focus on hyperlocal details too…
We don’t have enough minute studies on the impacts of climate change. What will happen to specific rivers in the Himalayas? What will happen to the Ganga?
We study the basic science and say “such and such a thing is happening”. But that’s not the end of the story. In fact, it’s often just the beginning.
We need more impact studies and in-depth research papers.
We need more minute observations with weather radar and wind profilers, especially over the oceans. We need more and more satellite observations.
We need huge computing resources, with AI and machine learning acting as key tools in weather forecasting, for which we need huge GPU-based computers.
We need more ground observations at the panchayat level. We need at least 20 times more data from here than we are currently collecting.
As far as India is concerned, as far as South Asia is concerned, the monsoon in particular is a red-button issue. We don’t have any control over these natural systems. The least we can do is attempt to understand them in depth.