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Predicting the Unpredictable: Why IMD is Spooked by Monsoon, Every Now and Then

Representational photo.

Representational photo.

While the national weather forecaster has significantly improved its prediction for the southwest monsoon over the years, a number of challenges still remain.

Legendary cartoonist R.K. Laxman always poked fun at the India Meteorological Department or IMD and its forecast, especially for monsoon rains. One of his best cartoons on the topic was where a person drenched in the rain is talking to two people with umbrellas, “That’s right. I belong to the weather bureau weather forecast section. How did you guess?”

Well, it definitely suited the times then. But IMD, the agency mandated with the job of forecasting weather, has come a long way. Right from tracking the slightest change in the weather system to accurately predicting cyclones, IMD has made use of technological advances and made significant improvements in its forecasting. And yet, every now and then, it is spooked by the monsoon.

Given the important role that monsoon plays in India’s economy and the loss of life and property due to extreme weather events, getting an accurate forecast with sufficient early warning is vital. Farmers look forward to accurate forecast and so do fisherfolks. People with livestock, those who work in the field too benefit from IMD’s forecast.

IMD’s forecast are awaited across India but nowhere more eagerly than the national capital that suffers a hot and humid June almost every year and gets ready to welcome the monsoon by June end. But this year, things went a little haywire for IMD’s predictions, an example sufficient to understand the unpredictability of the monsoon.

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Prior to and even on May 30 morning, IMD kept on forecasting that monsoon will hit Kerala coast around May 31. But by evening, it said, onset of monsoon over Kerala coast will be on June 3.

Monsoon parameters don’t change in hours and hence when asked by media, Dr Mrutyunjay Mohapatra, IMD’s Director General (Meteorology) had explained, “We are monitoring all the defined parameters/criteria for onset of monsoon over Kerala. At present, the criteria are not fully satisfied.”

Southwest monsoon did set over southern Kerala on June 3.

Then on June 12, IMD said, “conditions are favourable for further advance of southwest monsoon into most parts of Madhya Pradesh, remaining parts of East Uttar Pradesh, Delhi, some parts of West Uttar Pradesh, Haryana and Punjab during next 48 hours.” In other words, monsoon would reach on June 15. But on June 14, when monsoon had advanced into entire peninsular, east central and east and north-east India and some parts of north-west India, IMD said, “due to approaching of mid-latitude westerlies winds, further progress of monsoon over remaining parts of northwest India is likely to be slow.”

Since then, it has been an endless wait for Delhi, Haryana and Punjab. IMD has now made it clear that monsoon will be late in Delhi.

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Investing in ‘Monsoon Mission’

It is important to know how forecasting has evolved to understand how and why it fails sometimes. IMD’s seasonal prediction of southwest monsoon has been a well-documented process for more than 100 years, in fact since 1886. The prediction is based on empirical methods, evolving into the present-day dynamical modelling under the National Monsoon Mission.

Comparisons are often made with forecasting facilities in the western world, say the US or the UK, which have large number of weather stations and provide highly localised forecast. But IMD scientists claim there can be no comparison as those countries do not face the uncertain, highly dynamic monsoon and instead have just winds blowing from west to east 24 x 7 x 365, so predictions are easy, unlike in India where monsoon itself is a change in the wind system.

There are a number of methods that the IMD utilises, including using satellite images for monitoring. In fact, satellite monitoring has been in practice since the 1980s, but those images cannot predict conditions for say the next month.

IMD issues a ‘long range forecast’ for all four months of the southwest monsoon. Some of the physical processes are studied statistically, and it requires a lot of data, say of the last 50-60 years. The physics of the process does not change, it is everlasting. “But the statistical corelations change with time for whatever reasons yet unknown. In fact, corelations are never 100 per cent. At one point of time, IMD was looking at 16 parameters. But higher the number of parameters, more the confusion. Now there are five parameters because many of the corelations have been lost,” explained Dr Ranjan R. Kelkar, IMD’s former Director General (Meteorology).

That is the limitation with statistics: it works (better) for large scale and over a long period of time. For smaller things, dynamical models are used. In dynamical models, one applies lots of equations using the available data to arrive at a result, and this is done by a supercomputer. “The dynamical long-range forecasts are a parallel activity to the statistical forecast for long-range result,” Kelkar said.

Then there is a probability model and a numerical prediction model, but “each of the methodologies will have its own limitations”. Statistical forecast can help in validating past forecast and events, giving confidence that the models are working in the past and can be useful in the future. But not so in dynamical models, he added.

This year, IMD has adopted a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall by modifying the existing two-stage forecasting strategy. The new strategy is based on the existing statistical forecasting system and the newly developed Multi-Model Ensemble (MME)-based forecasting system. The MME approach uses the coupled global climate models (CGCMs) from different global climate prediction and research centres, including IMD’s Monsoon Mission Climate Forecasting System (MMCFS) model.

All these technological strides have been possible since the National Monsoon Mission (NMM) was initiated in 2012 with a budgetary allocation of Rs 551 crore and the broad objective to set up a dynamical prediction system for seasonal forecast and to improve the monsoon forecasting skills in the country. The High-Performance Computing (HPC) facility was augmented to a much higher level with a total investment of Rs 438.9 crore.

A November 2020 report titled ‘Estimating the Economic Benefits of Investment in Monsoon Mission and High Performance Computing facilities’ found out that the initial investment of ~Rs 1,000 crore in NMM and HPC facilities resulted in a 50-fold increase in its economic benefits.

Over and above the forecast for farmers and fisherfolks via SMS, there are a number of city-specific forecast issued by IMD. There are now-casts that issue alerts about any meteorological event in next three to four hours, be it thunder showers, lightning etc. And then, there are flood predictions. Unlike old times, IMD now uses several social media platforms apart from the conventional (such as AIR) methods to take the message across. But that has its limitations vis-à-vis language and internet penetration. Overall, it is work in progress.

On Friday, senior officials and representatives of the Ministry of Earth Sciences and even the private weather forecaster Skymet Weather briefed the Parliamentary Standing Committee on Science & Technology and Environment on the monsoon situation in India.

There is always hope that things will improve.

Disclaimer:Nivedita Khandekar is an independent journalist based in Delhi. She writes on environmental and developmental issues. She can be followed on Twitter @nivedita_Him. Views expressed are personal.

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first published:July 10, 2021, 15:30 IST