Question

write about the forecasting of monsoon.

Answer 1

The India Meteorological Department (IMD) is once again in the uncomfortable position of finding its prediction for the south-west monsoon going awry. Using a new statistical forecasting methodology, developed in consultation with Indian statisticians and published in an internationally reputed peer-reviewed journal, the department issued its long-range forecast for the monsoon in April, indicating that there could be a five per cent shortfall in countrywide rainfall, with an error bar of five percentage points. The updated forecast it issued at the end of June hiked the predicted deficit in rainfall to seven per cent with an error bar of four percentage points. Happily, the monsoon seems set to end with a surplus, if only a small one of about five per cent more than the long-term average. But that is no reason to abandon the new model and cast about frantically for a fresh way to foretell the monsoon’s outcome. A statistical model must be evaluated over a reasonable period of time and not on the basis of its performance in just one year. Since 2000, the IMD has thrice tweaked and changed the operational model it uses for long-range forecasting of the monsoon, and the new model deserves a fair trial.

In all of this, the primary purpose behind long-range forecasting of the south-west monsoon must be borne in mind. India’s Met Department began such forecasts more than a century ago. The government wanted advance warning of a drought as such a catastrophe could potentially set off a famine in those days. Although the spectre of famine has long been banished, a major drought, as happened in 2002, can still sharply reduce foodgrain production and curb the country’s economic growth. However, the monsoon has ended in a drought only 16 per cent of the time over the last 130-odd years while it has been ‘normal,’ with countrywide rainfall within 10 per cent of the long-term average, in seven years out of 10. The ability to predict a drought well in advance remains a challenge. The IMD’s new model, which might not have fared well this year, is expected to have a good chance of successfully doing so. But if the objective is to distinguish drought years from times when the monsoon is normal or on the excess side, then the long-range forecasts issued to the public need not try to quantify the amount of rain that will occur. Instead, the IMD ought to look at combining the output from its own models with information from other groups so as to provide the best assessment it can of the chances that the monsoon might be normal, bring excess rain, or end in a drought. This year, for instance, if the IMD had indicated that the odds favoured a normal monsoon, its prediction would have been correct.

Answer 2

Scientists have developed a new tool for objectively defining the onset and demise of the Indian Summer Monsoon—a colossal weather system that affects millions of people annually.

The researchers from Florida State University in the US developed a method that uses rainfall rates to mark the span of the Indian Summer Monsoon (ISM) at any given location throughout the affected region.

For generations, scientists have struggled to produce a model for reliably defining the duration of the monsoon. The researchers said that no existing system has allowed researchers to reliably define the parameters of the season at this fine a scale.

“Current weather forecasting and monitoring protocols focus attention on monsoon onset at one location—specifically the state of Kerala in the southwest corner of the country—and extrapolate for the rest of the region,” said Vasu Misra, associate professor at Florida State University.

“We have gone down to specific locations, we have covered the whole country, and we have objectively defined the onset and demise dates for any given year,” said Misra, lead investigator of the study published in the journal Climate Dynamics.

The lack of a clear, granular and objective benchmark for ISM onset and demise for all areas of the country has been a longtime source of consternation for people, researchers said.

In some parts of the country, the torrents of rain that characterise monsoon season account for more than 90 per cent of the total annual precipitation, they said.

Researchers said that many rhythms of Indian political and agricultural life can be destabilised by dubious or false claims of monsoon onset.

“That leads to tremendous amounts of frustration and confusion for the general public and for the people who are trying to monitor the monsoon because nobody has really gotten down to do it at a granular scale,” Misra said.

The new system, which ties the onset of the monsoon to location-specific rainfall thresholds, can work to allay that frustration, he said.

Up until now, regional meteorological departments have relied on their own ad hoc criteria for determining ISM onset, which can often lead to contradicting claims.

A more inclusive method will allow officials and researchers throughout the country to define the monsoon season using a standardised system that, through rigorous testing, has been shown to capture ISM evolution comprehensively.

“Anchoring the definition of onset and demise solely in local rain rates eliminates the need to rely on less accessible atmospheric variables,” researchers said.

This streamlined approach makes it considerably easier to monitor monsoon evolution, they said. “Our research enables quite easy real-time monitoring of the onset and demise of the Indian monsoon,” Misra said.

“We have tested this for 105 years of available data, and this criterion has not failed once for any location over India,” he said.