India's 2023 monsoon season ends at 94% of normal, regional variability remains

The India Meteorological Department on Saturday said that rainfall over the country, as a whole, during the monsoon season (June to September), was 94 per cent of its long period average.

It said that seasonal rainfalls over northwest, central India, south peninsula, and northeast India were 101 per cent, 100 per cent, 92 per cent and 82 per cent of respective long period average.

Rainfall ranging from 94 percent to 106 percent of the long-period average (LPA) is categorised as normal.

Nonetheless, it's important to note that even when cumulative rainfall during the monsoon season is considered normal, it doesn't necessarily guarantee an evenly distributed spread of precipitation across both space and time.

The Indian monsoon is subject to inherent fluctuations and changes that transpire over time due to a variety of natural factors, collectively referred to as natural variability. According to IMD Director General Mrutyunjay Mohapatra, the 2023 monsoon concluded with 94.4 percent cumulative rainfall, classified as "normal" due to the presence of favourable factors that countered the impact of El Nino.

"Out of the total 36 meteorological subdivisions, 3 subdivisions constituting nine per cent of the total area of the country received excess, 26 subdivisions received normal rainfall (73 per cent of the total area) and seven subdivisions (18 percent of the total area) received deficient season rainfall," said Mohapatra at a press conference.

The seven meteorological subdivisions which got deficient rainfall are Nagaland, Manipur, Mizoram & Tripura (NMMT), Gangetic West Bengal, Jharkhand, Bihar, east UP, south interior Karnataka, and Kerala.

"Monthly rainfall over the country as a whole was 91 per cent of LPA in June, 113 per cent of LPA in July, 64 per cent of LPA in August, and 113 per cent of LPA in September," the IMD chief said.

The IMD had predicted a monsoon season for India that falls within the range of "normal," though leaning towards the lower end of the spectrum. They had, however, issued a caution that the presence of El Nino, a phenomenon characterised by the warming of Pacific Ocean waters near South America, might exert its influence during the latter half of the southwest monsoon.

El Nino conditions are typically associated with weaker monsoon winds and drier weather patterns in India. During this year, India witnessed a rainfall deficit in June, followed by excessive precipitation in July. This abrupt change was attributed to consecutive western disturbances over northwest India and a favourable phase of the Madden-Julian Oscillation (MJO).

"The MJO, known for enhancing convection in the Bay of Bengal and the Arabian Sea, is a large-scale atmospheric disturbance originating in tropical Africa and travelling eastward, typically persisting for 30 to 60 days," as per the IMD Director General.

August 2023 went down in the records as the driest month since 1901 and the hottest ever recorded in India, a phenomenon attributed to the strengthening of El Nino conditions. However, September brought a surplus of rainfall, thanks to the presence of multiple low-pressure systems and a positive phase of the MJO.