Southwest monsoon seasonal rainfall has been revised based on data from 1971-2020. The new seasonal long period average (LPA), now stands at 868.8mm for the 4 month long season from June to September. Earlier, based on data from 1961 – 2010, the LPA was 880.6mm, therefore a decrease of 12mm. In the beginning of this century, the LPA was still higher at 892mm and so a slump of nearly 24mm in the seasonal rainfall.
Truly speaking, the long period rainfall need to be revised after every 10 years over a data base of last 50 years. On completion of decade, the earliest one, need to be replaced with the current, as has been done in the last revision. However, rainfall revision has been done even arbitrarily, in the recent past, amounting to multiple figures of LPA between 2001 and 2022.
It is evident that the seasonal rainfall is mostly shrinking and has dropped by 24mm, since the beginning of this century. Expectedly, the next revision falls due on 2031 based on data between 1981-2030. Since 2001, there have been 5 droughts ( 2002, 2004, 2009, 2014, 2015), 2 of these in 2002 and 2009 being severe. Rest of the 3 droughts remained light to moderate with rainfall deficiency of 12% - 14%. In between, the year 2018 narrowly missed another drought with seasonal shortfall of -9.4%.
Since 2001, the year 2019 has been the rainiest with a seasonal figure of 971.8mm, a surplus of 9.96% against the LPA of 880.6mm. The poorest of all was the year 2009, a severe drought, with a huge deficit of -21.8%. Incidentally, this also was the highest since 1972, when the scanty season left a scar of -23.9%. Also, 1972 happens to be the 3rd highest shortfall in the history of severe drought, ever recorded since 1871. The most oppressive monsoon ever was in 1877 with a disparity of -28.8% and the 2nd cruel monsoon in 1899 having seasonal sagging of -25.8%.
Indian Summer Monsoon Rainfall (ISMR) has witnessed hat-trick of normal / above normal monsoon between 2019 and 2021. Skymet has predicted another normal Monsoon 2022, making it 4 in a row. The recent history has a record of six successive normal monsoon between 1993 and 1998. Southwest monsoon has decadal cycles of dry and wet epochs. The decade 2021-2030 is expected to come closer to the neutral before entering wet epoch, likely between 2031-2040.