The three decades from 2020 to 2049 are likely to have frequent disastrous droughts in the Indian summer monsoon, says the paper
New Delhi: India is reeling under severe water crisis and rural distress as the country faced two consecutive deficient monsoon seasons in 2014 and 2015. But the worst is yet to come as more frequent drought monsoons are expected to come India’s way between 2020 and 2049, according to a scientific paper to be published in Current Science. The paper was first reported by The Indian Express.
The study refers to past rainfall records to understand why this is likely to happen.
After India began taking rainfall measurements since the 1840s, it was observed that the country has three-decade-long periods or epochs of alternating dry and wet monsoons. For example, during the dry epoch 1960-89, there were 10 monsoon drought years, but during 1930-59, India had only two drought monsoons. And so the cycle has been observed from 1840 to 1989.
Met experts found this alternating nature of dry and wet tri-decadal phases to be associated with the cold phase of the Atlantic multi-decadal oscillation in sea surface temperature. Curiously, the 1990-2019 epoch was expected to be a wet one, going by the cycle of the ocean-atmosphere system of the earlier 150-year period. 2014 and 2015 were part of a three decade period, 1990-2019, which was supposed to have more good monsoons and very few bad monsoons. But while 1990 to 2000 saw no drought monsoons, the following two decades have seen five drought monsoons so far (2002, 2004, 2009, 2014 and 2015).
“...the frequent drought scenario has reappeared after the first decade of the expected wet epoch. The cooling trend of the Asian upper troposphere over Central Asia is believed to have caused this," explains the paper authored by researchers from Kochi-based Nansen Environmental Research Centre India and Pune-based Indian Institute of Tropical Meteorology (IITM).
Using data from a network of 306 climatological rain gauge stations well distributed over India, scientists at IITM, Pune have derived an Indian summer monsoon rainfall series for the period 1871 to the current year, which was used for this paper.
These dry periods or dry epochs see not only frequent drought monsoons, but also a high percentage of severe cyclones in the Bay of Bengal which would move upwards with disastrous impact in Bangladesh, Myanmar, and Odisha and West Bengal in India.
The paper concludes that going by this natural cyclicity of the ocean-atmosphere system, the three decades from 2020 to 2049 are likely to have frequent disastrous droughts in the Indian summer monsoon and a large percentage of the severe cyclones of the Bay of Bengal are likely to have northward track, adversely affecting the coastal region of north Bay of Bengal.
The paper further reveals that the recent dry epoch of 1960-1989 had a cold upper tropospheric temperature anomaly over Central Asia and that this cold anomaly region has also experienced a long-term cooling trend. “(This) cooling trend over the Asian continent is likely to make it even more severe in its impact than 1960-89," the paper said, adding that the frequency and severity of droughts expected during 2020-49 is likely to be higher than that of the recent dry epoch 1960-89.