Wet epoch of monsoon to start from 2031
There is a decrease of 12.0mm in monsoon and 16.8 mm in annual rainfall between 19612010 and 1971-2020. The decrease is part of natural multi-decadal epochal variability of dry and wet epochs of all India rainfall, IMD said in a statement.
“The southwest monsoon is passing through a dry epoch which started in the decade of 1971-80. The decadal average of all India southwest monsoon rainfall for the decade 2011-20 is -3.8% of the long-term mean. 2021-30 is expected to be come closer to neutral and southwest monsoon will enter the wet epoch from the decade, 2031-40,” IMD said.
The rainfall “normal” is prepared based on the data for the period of 50 years and is updated periodically once a decade by incorporating the latest data from rain gauge stations, IMD said. The new updated rainfall normal has been prepared based on data of 1971-2020 and will replace the existing rainfall normal based on 1961-2010 with effect from this monsoon season. During monsoon, India receives about 868.6mm rainfall which is about 75% of the annual rainfall (1160.1mm). Out of 12 months, July receives maximum rainfall of 280.4mm followed by August (254.9mm). Konkan and Goa receive highest rainfall of more than 300cm annually followed by subdivisions in the northeastern India which have annual rainfall normal between 200 to 280cm. West Rajasthan receives lowest annual rainfall of about 33cm.
“Since 1980s we have been seeing a below normal phase of monsoon. Before that it was in the above normal epoch for a few decades. This is decadal variation in monsoon rain. Now, we are gradually turning towards a period when we can expect normal monsoon rain and above normal thereafter. So we should expect more rainfall,” explained DS Pai, former scientist at the weather bureau, and now director at the Institute of Climate Change Studies, Kerala. “The frequency of heavy rainfall events is increasing so more rain can be detrimental. For example, if there is extremely heavy rain during sowing the seeds can wash away or in other times fertilisers can wash away. The timing is important,” he added.