The India Meteorological Department (IMD) has upgraded its original monsoon forecast and said on Tuesday that seasonal rainfall in the country would be 98 per cent of long-period average (LPA) for the June-September period, with a model error of 4 per cent, plus or minus. IMD's first monsoon forecast in April said that the monsoon would be 96 per cent of the LPA.
IMD categorises rainfall in the 96-104 per cent LPA range as normal, while anything immediately below that is considered below normal. As per the 1951-2000 baseline, India receives average seasonal rainfall of 89 cm.
The indications of a weak El Niño and favourable conditions over the Indian Ocean are among the chief reasons for the upgrade in the forecast, IMD officials said. El Niño is an abnormal condition over equatorial Pacific Ocean, with warming over central and east Pacific Ocean. The warming results in below-par rainfall across the subcontinent and South Asia.
Even as IMD's own monsoon mission coupled forecasting system indicated probability of neutral El Niño conditions till the end of this year, weather bureaus indicated a 60-per cent probability of weak El Niño conditions during the second half of 2017.
This year, the IMD has operationalised the dynamical model of forecasting while continuing to use the older ensemble statistical model that has been in use since 2007. "Along with an all-India forecast, we have also indicated spatial distribution of rainfall for different regions and at present, that cannot be generated through the dynamical model, which has to be put through more rigour," said Madhavan Nair Rajeevan, Secretary, Ministry of Earth Sciences.
