Southwest monsoon could switch into a drought-prone mode, lasting decades in the future
India witnessed repeated multi-year droughts over the last thousand years, predominately before 1871, a new study has predicted.
This contrasts with the drought history of the post-1871 era. The country saw only one instance of a three-year-long drought during this period, from 1985-1987, the study published September 19, 2022, in the journal Proceedings of the National Academy of Science highlighted.
Subcontinent-wide severe droughts, too, have become rare, with only five such instances over the last 150 years.
The southwest monsoon could switch into a drought-prone mode, lasting decades in the future, the authors of the study warned.
India’s current water resources, sustainability and mitigation policies do not consider the possibility of multi-year droughts in the future. The researchers make a case for reassessing policies.
Gayatri Kathayat and her colleagues arrived at these findings by reconstructing monsoon records.
“We have 150 years of instrumental data. But we did not know what monsoons looked like in the past. Everything was like a black hole,” Kathayat, an author of the study, told Down To Earth.
This quest took them to Mawmluh cave, Cherrapunji, one of the wettest regions in the world.
The researchers studied geological formations called stalagmites, mineral deposits formed by flowing, dripping, or seeping water to make the reconstruction possible.
These long cylindrical structures act as record-keepers of past climates. The researchers estimated the value of delta O-18 from these structures.
Delta O-18 measures the ratio of stable isotopes or variants of oxygen. A positive delta O-18 value signals drier conditions, while a negative one indicates wetter conditions, Kathayat explained.
They compared their data with documented drought records, famines, mass mortality events and geopolitical changes in the Indian subcontinent.
Droughts are the reasons behind most famines in India before the British period, between the 1500s and 1770s, the study noted.
Their data agreed with documented records of severe droughts in the late 18th and early 19th centuries.
Deindustrialisation occurred in India by mid 19th centuary as the country lost most of its export market, the report found.
This supports the theory that a “drastic slump in agricultural productivity and the fragmentation of the Mughal Empire sowed the seeds of India’s deindustrialisation,” the researchers wrote.
Climate, possibly, led to India’s deindustrialisation, they added.
Only roughly 20 per cent and 50 per cent of the historic droughts appear to have co-occurred with the El Nino event. El Nino is a climate pattern describing the unusual surface water warming in the eastern equatorial Pacific Ocean.
Peaks in El Nino activity in the 1640s and 1800s corresponded with increased historical drought frequency, the study showed.
This is consistent with patterns post-1871. Less than 50 per cent of the southwest monsoon droughts have co-occurred with the El Nino events, the researchers pointed out.
This suggests other factors could have also been involved.
The researchers hope to gain more insights into the drivers of multi-year droughts. “We know when it happened and where it happened. But we don’t know why it happened,” Kathayat added.
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