India Meteorological Department: India Meteorological Department springs up new rainfall normal
india meteorological department: india meteorological department springs up new rainfall

India Meteorological Department: India Meteorological Department springs up new rainfall normal

The India Meteorological Department (IMD) has come out with a new rainfall normal by computing the long period average (LPA) for 1971-2020, shifting from the data for 1961-2010 used earlier.

The new all-India rainfall normal computed for the southwest monsoon season (June-September) is 868.6mm, less than the earlier normal of 880.6 mm.

The new all-India annual rainfall normal based on 1971-2020 data is 1160.1 mm compared to the earlier normal of 1176.9mm using the 1961-2010 data.

There is a decrease of 12.0 mm in the mean rainfall for the southwest monsoon season and 16.8 mm in annual rainfall for the country as a whole from 1961-2010 to 1971-2020.

“The above decrease is part of natural multidecadal epochal variability of dry and wet epochs of all India rainfall,” the IMD said, adding that the southwest monsoon is passing through a dry epoch that started in the 1971-80 decade.

“The next decade i.e. 2021-30 is expected to come closer to neutral and southwest monsoon would enter into the wet epoch from the decade 2031-40,” it said.

The new rainfall normal has been computed using rainfall data from 4,132 rain gauge stations across the country, representing 703 districts of India.

Based on the new data, the southwest monsoon rainfall over India contributes 74.9% to the annual rainfall.

June, July, August and September account for 19.1%, 32.3%, 29.4% and 19.3% respectively of the total southwest monsoon seasonal rainfall.

All-India pre-monsoon season (March-May) rainfall (130.6mm) and post-monsoon season rainfall (121.0mm) account for about 11% and 10% respectively of the annual rainfall.

Gujarat region receives the highest rainfall, 96% of its annual rainfall, in the southwest monsoon season while Tamil Nadu receives 48% of annual rainfall in the northeast monsoon season (October-December), followed by 36% in the southwest monsoon season, according to the data.

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