IMD predicts a normal monsoon

India Meteorological Department (IMD) on Monday forecast that the monsoon this year will be normal, with rainfall of 97 percent of the long period average (LPA) with an error of plus or minus five percent. 

If the forecast comes true, it will benefit the country’s economy, as it will be the third successive normal monsoon year. The country had recorded a rainfall of 97 percent in 2016 and 98 percent last year during the season which runs from June to September. 

The long period average for the season is calculated on the basis of the mean rainfall during the four-month monsoon season over a 50-year-period from 1951-2010. It comes to an average of 89 cm for the country as a whole. 

Announcing the forecast, IMD director general K.J. Ramesh, said the forecast was based on both statistical ensemble forecasting system and a dynamic global climate forecasting system. The dynamic model has forecast a rainfall of 99 percent plus or minus a model error of five percent, while the statistical model forecast is 97 percent plus or minus a model error of five percent. 

IMD would come out with an update in early June. At that point of time, apart from an updated forecast for the country as a whole and the season in its entirety, the department would issue separate forecasts for rainfall for the months of July and August for the country as a whole and season-wide rainfall for the four distinct geographical areas--north-west India, south peninsula, northeast India and central India. 

Dr Ramesh also announced category-wise forecast in terms of probabilities for normal (96 percent to 104 percent), above normal (104 percent to 110 percent), excess (more than 110 percent), below normal (90 percent to 96 percent) and deficient (less than 90 percent) rainfall. There was a probability of 42 percent for a normal rainfall, followed by 12 percent for above normal, 30 percent for below normal, two percent for excess and 14 percent for deficient rainfall. “There is thus the maximum probability of normal rainfall and low probability for deficient rainfall," he said.  

Referring to various global and regional factors that influence Indian monsoon, he said, the El Nino-La Nina factor is expected to be normal this year. A moderate La Nina condition had developed in the equatorial Pacific during last year. It, however, started weakening in the early parts of this year and has currently turned into a weak La Nina condition. The latest forecasts from Indian and global models indicate that it will go away before the beginning of the season. 

As regards Indian Ocean Dipole phenomenon, which is the other important factor, he said that at present neutral IOD conditions are prevailing and the recent forecasts indicate that weak negative IOD conditions may develop during the middle of the monsoon season and this has been factored into the overall forecast. IMD would continuously monitor the situation,” he added. (India Science Wire)