How ISM variability led to more showers in the Bay

Subject: Geography

Subject : Climatology/ Atomosphere

Context:

Regions surrounding northern Bay of Bengal (BoB) received higher precipitation than the other parts of India for the last 10,200 years, says a new study.

About the study and its findings:

Birbal Sahni Institute of Paleosciences, Lucknow, reconstructed the history of the ISM variability from this region by using both biotic (phytoliths, NPPs and stable carbon isotopes) and abiotic (environmental magnetic parameters, and grain size data) proxies that predate instrumental records (records taken before the 19th century).
This new study traced the dynamics of Indian Summer Monsoon Rainfall (ISMR) over 10,000 years – a period which witnessed the development and fall of numerous ancient civilisations around the world, many of which were associated with climate instability.
The researchers show that a heavy ISMR was witnessed between 10,200 years and 5,600 years ago by this region, but the ISMR decreased 4,300 years ago.
The ISM got strengthened again between 3,700 and 2,100 years following which it switched to a drier mode for a while.
The ISM regained its strength some 200 to 100 years ago. Of the weakened phases, the one that occurred around 4,300 years back was the most severe one, and had an adverse impact on the ecosystem.

What derived the variability in ISM?

As per the study, the millennial-scale variations in the ISM rainfall may largely be attributed to changes in solar insolation and dynamics of the inter-tropical convergence zone (ITCZ — an area where the northeast and the southeast trade winds converge).
The centennial-scale variations may be collectively triggered by phenomena like North Atlantic Oscillation, El Nino Southern Oscillation and Indian Ocean Dipole.

Significance of the study:

Indian agriculture is heavily dependent on ISM.
The Bengal Basin located at the trajectory of the Bay of Bengal (BoB) branch of the ISM is very sensitive to changes in the ISM strength.
Even a minor change in ISM strength may have adverse effects on the agrarian-based socio-economic conditions of the region.
However, no systematic long-term record (beyond the range of instrumental period) for the past ISM variability in the region was available.
The study can help us understand long-term trends of climate change impacts on the ecosystems and may help mitigate future climate extremities.