Near-normal monsoon hope

TT, New Delhi, April 18: India's monsoon rainfall in 2017 will be close to its normal average amount, the India Meteorological Department (IMD) said today in its preliminary long-range forecast for the summer rainfall crucial for the country's crops and economy.

The IMD said rainfall during the four-month monsoon season starting June will be 96 per cent of the long-period average and that its first assessment suggests a 38 per cent probability for a near-normal rainfall within 96 and 104 per cent of the average.

"We expect a normal monsoon, which will be good for our agriculture and good for economy," said K.J. Ramesh, director-general of the IMD, which has this year for the first time combined two forecasting techniques to issue its monsoon forecast.

The weather agency departed from its own tradition and declined to make public the probability values for other ranges of rainfall amounts - excess, above normal, below normal, and deficient.

Ramesh and two senior meteorologists said the IMD would release the full probability distribution for different ranges of rainfall amounts in its updated long-range forecast due in early June. The updated information will provide separate forecasts for monthly rainfall in July and August and for various geographical regions of India.

Crop meteorologists view the rainfall during July and August as critical for agriculture, particularly for the transplanting of paddy. Maize, soybean, pulses, and sugarcane are among other key crops sown across the country during the summer monsoon season.

The IMD has over the past decade relied on a statistical model that measures the values of five key weather-related parameters worldwide, including sea surface temperatures in the eastern and central Pacific Ocean, to issue long-range monsoon forecasts.

The Pacific sea surface temperatures determine the so-called El Nino phenomenon - a slight increase in the sea surface temperatures - that has been linked to poor monsoon behaviour in India.

Global forecasts suggest the El Nino is likely to develop during the second half of the monsoon season, but IMD meteorologists assert that it is too early to say what impact, if any, it will have on the 2017 monsoon.

Statistically, an El Nino year is more likely to be a deficient monsoon year.

"But there is no one-to-one relationship between El Nino and the monsoon," said D. Sivananda Pai, head of the forecasting team at IMD Pune.

Among 15 El Nino years between 1951 and 2016, nine years had deficient monsoon (below 90 per cent of the long period average), while four had monsoon levels between 90 and 100 per cent of the average, and two years experienced rainfall greater than 100 per cent of the average.

The 2017 forecast, for the first time, incorporates a dynamic global climate forecasting model that uses computers and real-time weather data from around the world to generate forecasts of the monsoon's performance.

"The forecasts for the 2017 monsoon from the statistical model and the dynamic model are both 96 per cent," said Madhavan Rajeevan, a senior meteorologist and secretary, the ministry of earth sciences, which had supported the development of the dynamic model.

Senior meteorologists explained that including the dynamic model into the 2017 forecast has "complicated" the probability distribution of rainfall amounts because the process of "reconciling" the probabilities generated by the statistical model forecast and the dynamical model forecast is difficult.

"Rather than release multiple numbers that might appear confusing, we decided that we will release only the highest probability figure which is for near normal monsoon," a senior scientist said.