Monsoon rains in India are likely to be “normal” this year, the India Meteorological Department (IMD) said on Monday. However, uncertainty clouds this optimism as the agency’s own assessment suggests a significant probability for rains falling in the ‘below normal’ category.
Monsoon rainfall this year is forecast to be 96% of the Long Period Average (or 89 cm, which is a 50 year average of India’s monsoon rains).
Strictly speaking, a 96% forecast is, in the IMD lexicon, “near normal.” This is just shy of ‘below normal’ (90%-96% of LPA) rain.
However, Madhavan Rajeevan, Secretary, Ministry of Earth Sciences (to whom the IMD reports), at a press conference emphasised that this year’s forecast was for “normal” rains. “For all practical purposes, we expect normal rains,” he added.
This is a more optimistic assessment from the one by private weather forecasting agency, Skymet, which earlier this month, warned of ‘below normal’ rains June-September.
The IMD’s optimism stems from global climate models projecting a ‘weakening El Nino.’ The El Nino, a cyclic warming of the Central and Eastern Pacific region, has historically been linked to a weakening of monsoon rain.
A temperature rise greater than 1 degree C for three months at a trot, is considered a ‘strong’ El Nino (and threatening to the monsoon). A 0.5C -1C rise is called ‘weak El Nino conditions.’ Currently the El Nino is 0.9 C.
The IMD’s models in March, expect the El Nino to peak around May and then recede for the rest of the monsoon months. “Globally too, other models that track El Nino expect it to recede after June or July. So that reflects in our forecast (of a normal as opposed to below normal monsoon rains),” said Mr. Rajeevan. In any given year, the odds of ‘below normal’ rains are 17%.
This year — the IMD’s assessment says — the odds are 32% which Mr. Rajeevan admitted was “significant.” However the odds of ‘near normal’ rains this year were 39%, the IMD’s forecast notes. “It’s a matter of how you expect the El Nino to pan out…we combine our own experience with the model’s insights to make the forecast,” said K.J. Ramesh, Director-General, IMD.
The IMD issues its first monsoon forecast in April and then updates it in June with details on how the monsoon will perform in various geographical regions.
The April forecast can be unreliable. Last year, the IMD forecast ‘normal rains’ (97% of LPA) and India saw below normal (91% of LPA) rains. This was attributed by the IMD, to an unexpected weakening of the monsoon rains in North Eastern India.
Another factor, called a positive Indian Ocean Dipole (IOD) (which refers to a warming in the western Arabian ocean) could neutralise the potential negative impact from the El Nino.
