The India Meteorological Department (IMD) has stated that the country will experience normal monsoon (96 to 104 per cent of Long Period Average) this year. The announcement was part of the IMD’s first stage Long Range Forecast (LRF) released on Friday.
During the online briefing, IMD Director General M Mohapatra said the quantitative rainfall during the upcoming June to September season would be 98 per cent of the LPA, which falls under the normal rainfall category. The country’s LPA for the southwest monsoon season is 88 cm, calculated over the period 1961-2010.
The LPA range to ascertain the category of rainfall is - below 90 per cent LPA is considered deficient; between 90-96 per cent LPA is below normal; 96-104 per cent LPA is normal; between 104-110 per cent is above normal and above 110 per cent LPA is excess.
Earlier this week, private weather forecast agency Skymet Weather too predicted that the monsoon this year was likely to be 103 per cent of the Long Period Average (LPA). The agency classified it as a ‘healthy normal’ in a press conference on Tuesday.
The southwest monsoon brings about 70 per cent of the country’s annual rainfall. The IMD issues the LRF in two stages, during April and June, every year. However, some areas in northeast India, along with Odisha, Jharkhand and Bihar, could experience a slightly below average monsoon.
“There is a good start, very good news that the monsoon situation in the country this year will be normal. This will be good for our agriculture. If realised, this will be the third consecutive year when the country’s monsoon would be normal,” said an IMD official.
He added, “However during 2021 monsoon, we might see the development of El Nino conditions.”
El Nino Southern Oscillation (ENSO) is one of the many large-scale features that influence the Indian summer monsoon. Though there are no direct established links between the El Nino, which is the abnormal warming of the equatorial Pacific Ocean and the monsoon, it has been observed that rainfall during El Nino years remains subdued. Likewise, La Nina, the opposite of El Nino, is known to favour the Indian summer monsoon. Closer home, the Indian Ocean Dipole (IOD) is another ocean phenomenon factored in at the time of issuing monsoon forecasts.
According to Skymet, the LPA refers to the average all-India monsoon rainfall of 88 cm, which is a 50-year mean. “The monsoon that concluded in 2020 was unique in that, with monsoon 2019, it was only the third time in a century that India saw back-to-back years of above-normal rainfall, which is defined as rainfall that’s 5 per cent above normal (105 per cent),” the private weather agency stated.
Starting this season, the IMD will use the guidance of Multi-Model Ensemble, that is, consider collective inputs gathered from multiple weather models. Since 2017, the IMD has been also using a high-resolution dynamical global Climate Forecasting System, developed under the Monsoon Mission of the Ministry of Earth Sciences.
Besides, the Met department plans to issue a special monsoon forecast for the Monsoon Core Zone — spanning across Madhya Pradesh, Maharashtra, Chhattisgarh, Jharkhand, Odisha, Rajasthan, Gujarat along with parts of Bihar and Karnataka.
As sea surface temperature (SST) conditions over the Pacific and the Indian Oceans are known to have strong influence on Indian monsoon, the IMD is carefully monitoring the evolution of sea surface conditions over these 0cean basins, the official said.
The IMD will issue updated forecasts in the last week of May 2021. In addition to the update for the April forecast, forecasts of the monsoon season (June-September) rainfall for four homogenous regions and for June also will be issued, the IMD informed.