Too early to cheer for a normal monsoon this year

Hold your horses. It is too early to cheer for a ‘normal’ monsoon this year. On February 25, Skymet Weather, a private weather forecasting agency, issued its ‘ preliminary monsoon forecast guidance for 2019 ‘, informing it expects over 50 per cent chance of the upcoming monsoon to be ‘normal.’

The weather agency noted that El Niño had been on a rise till last December, but was showing a consistent drop. And this trend of devolving El Niño “would surely not lead to a drought”. El Niño , when sea surface temperatures in the tropical Pacific Ocean rise to above-normal levels for an extended period of time, is often associated with deficient southwest monsoon rainfall in the country.

While releasing its preliminary forecast, Skymet mentioned it was “a bit early to share the complete details as data is still being collected and the information is getting collated”, and a ‘detailed monsoon forecast’ would be issued between March 15 and April 15.

Meanwhile, the news of the likelihood of ‘normal’ monsoon is all over the place. But before we get into a rejoicing mood, let us remember that last year both Skymet and the India Meteorological Department (IMD), country’s official weather forecasting agency, had forecasted a ‘normal’ monsoon.

In its first stage long-range forecast issued last April 16, the Met department had predicted ‘normal rainfall of 97 per cent of the long period average, or LPA, with a model error of plus or minus 5 per cent. 

The Skymet had predicted normal rainfall of 100 per cent of the LPA with “zero per cent chance of drought”. The LPA is the weighted average of rainfall India received in June September from 1951 to 2000 and is pegged at 89 cm.

In spite of a forecast of ‘normal’ monsoon, by the end of last southwest monsoon season (June to September), the rainfall departure in the country was nine per cent, which is considered ‘below normal’.

One after the other, several states have declared drought. And at present, almost half the country is facing drought with at least 16 per cent falling in the extreme drought category, as mapped by the drought monitoring system of the Indian Institute of Technology, Gandhinagar.  Some climate scientists claim it is too early to issue any forecast on the Indian summer monsoon. According to Sridhar Balasubramanian, associate professor of mechanical engineering and an adjunct faculty in IDP Climate Studies at the Indian Institute of Technology-Bombay, 50 per cent chance of ‘normal’ monsoon is a safe bet because it is neither normal nor abnormal, and doesn’t convey anything. 

At present, the predictive capability of the dynamical models for prediction of any synoptic event three months in advance is very poor. Therefore, any such prediction should be taken with extreme caution.

Also, the term ‘normal’ monsoon itself is questionable because of high state-wise and district-wise variability of rainfall across the country. Even with ‘normal’ monsoon rainfall, there are floods and droughts in the country. 

Forecasting monsoon at this time of the year is challenging because of the “predictability barrier”. Simply put, it means there is a predictability barrier around spring time for El Niño.

The IMD has been issuing seasonal forecasts since 1886 and has been receiving requests for an early prediction of monsoon, especially before the Union Budget. 

M Rajeevan, secretary, Union ministry of earth sciences, says that the Met department has tried and carried out lot of research, but found it is not worth giving early forecasts.

Hence, the IMD has a two-stage strategy for the monsoon forecast. A tentative forecast in issued in April followed by an updated forecast in the last week of May or first week of June. By that time, there is a better understanding of El Niño evolution.

Apart from the El Niño, there are other factors, such as Madden- Julian Oscillation propagation, Indian Ocean Dipole, strength of monsoon currents, and the intra-seasonal oscillations of the monsoon that influence the summer monsoon.

Rajeevan informs there is no one to one correspondence between monsoon and El Niño. There are drought years even without El Niño, and in El Niño years, we have had good monsoons like in 1997.

Let us not count chickens before they hatch.

The author is an independent journalist