Southwest monsoon ends with over 8% surplus

First time since 2010 that India has got more than 100% of its long period average in consecutive years

India has never got over 105% of the long period average in consecutive years in at least 30 years, according to records available since 1988 on the IMD website.

The southwest monsoon this year has ended with an 8.7% surplus, surpassing estimates by the India Meteorological Department (IMD). This was also the first time since 2010 that India has got more than 100% of its long period average (LPA), of 88 cm, in consecutive years. Last year India saw record rainfall of 110% of the LPA, the highest in a quarter century.

India has never got over 105% of the LPA in consecutive years in at least 30 years, according to records available since 1988 on the IMD website.

“These have been an unusually good couple of years for the monsoon,” said D.S. Pai, Chief Forecaster, National Climate Centre, IMD Pune. “There are larger trends that statistics show of a decadal swing in overall monsoon rainfall. The last two decades however have been weak and hopefully, what we see now is the beginning of a new epoch.”

Low-pressure systems

The heavy rains this year have been due to several long-lasting low-pressure systems in the Bay of Bengal that fuelled heavy rains over large swathes of India in August. This wiped out the rainfall deficit in July, which is usually the rainiest of the four monsoon months. At 32 cm, August rainfall was nearly 26% more than what’s usual for the month.

A developing La Nina, the converse of an El Nino, which is a heating of the central equatorial Pacific and responsible for diminished monsoon rain over India, too contributed to munificent rains this year. The IMD in its forecasts had anticipated ‘normal’ rain, defined as 96-104% of the LPA. Rains above 110% LPA are termed ‘excess’ and this year has fallen only a tad short.

The IMD would be presenting a detailed analysis along with historical context in its ‘end-of-season’ report expected this week, said Mr. Pai.

The monsoon has started to withdraw from northern India and is expected to do so until the northeastern monsoon sets in by mid October. Rainfall was well distributed across most of India this monsoon. Central India got 15% more and South India 29% more than their regional normals. Northeast India got 6% and northwest India posted a 15% deficit.

Of the 36 meteorological subdivisions that the IMD has partitioned the country, 12 recorded ‘excess’ rains and 17 recorded ‘ normal’ rains. Only five divisions posted ‘deficient rains.’