India is likely to receive “normal” monsoon rainfall this year, the India Meteorological Department (IMD) has said as part of its official April forecast. Except for parts of eastern and northeastern India, many parts of the country are expected to get “above normal” rainfall, the IMD’s models show.
“Normal” rainfall refers to a range: 96%-104% of the Long Period Average (LPA) of 88 cm.
Earlier this week, private weather forecasting company, Skymet Weather, too, said it expected India to get normal rainfall but said this was likely to be 103% of the LPA, whereas the IMD, on Friday, has estimated it to be 98% of the LPA.
The April forecast, which is based on an analysis of select meteorological factors in March, is updated in May along with estimates of how the monsoon will perform in different geographical regions. In 2019, the IMD forecast 96% LPA in April but India ended up with record excessive rainfall of 110%. In 2020, it said 100% LPA but India wound up with 109%. IMD officials, however, said that it was unlikely there would be such excessive rain this year.
In 2019, the Indian Ocean Dipole, or an IOD — defined as a swing in temperatures in the western and eastern sections of the Indian Ocean, where a positive phase usually corresponds to good rains over India — contributed to the excess rains. Last year it was La Nina — the converse of an El Nino and associated with a cooling of the equatorial central Pacific — again a feature correlated with heavy India rains.
“This year, the models show a weak IOD and neutral conditions in the central Pacific. It’s unlikely there will be over 105% LPA this year,” D.S. Pai, a meteorologist with the IMD’s National Climate Centre, Pune, told The Hindu .
Though the IMD now issues short-term and extended range forecasts — that is, an estimate of rainfall in time frames of 3 days to 15 days — for the first time this year, it will begin giving monthly forecasts for all months.
It has so far refrained from giving a forecast for June and September, months that are known to be erratic as those are the months when the monsoon enters and exits the country, respectively, posing a challenge to meteorologists. Dr. Pai, however, said that the IMD’s work for several years in honing the skills of a class of models, called dynamical models, has improved their forecasting abilities over three weeks. “So we can now extend it to monthly forecasts. The overall aim of these models is to be able to accommodate changes in the global weather that will influence the monsoon. This is more useful for planning,” he said.
The IMD also said that it was developing a separate forecast for the Monsoon Core Zone (MCZ), which represents most of the rainfed agriculture region in the country. “A separate forecast for the MCZ will be more useful for agricultural planning and crop yield estimation, etc. In the second stage forecast in May, IMD will issue a separate probabilistic forecast for the MCZ, based on MME system and a new statistical model,” said a statement.
Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology, Pune, tweeted that the reduction in rainfall in eastern India has been consistently decreasing. For adequate monsoon rain, it is important for a temperature gradient to be present between the ocean and the land. In recent years, however, the India Ocean has been warming faster than the land surface, reducing this temperature differential and affecting the monsoonal flow.
