Rainfall drop likely due to 60% drop in low pressure over Bay of Bengal forecast by scientists

A steady rise in atmospheric temperature is likely to rob Indian monsoon of its lifeblood multiple low pressure zones or storms that formed over the Bay of Bengal every year between June and September.

An Indo-US team of scientists has warned about a 60% drop in the number of low pressure systems over the bay towards the end of 21st century as the global temperature rises, which could lead to a significant decrease in monsoon rainfall.

What further adds to the woes of the monsoon is a clear signature of how more and more such low pressure zones would form over the Indian landmass and not on the sea.

Due to this shift to landmass, these low pressure systems would carry much less water. As a result, there may be a little increase in smaller spell of intense rainfall in north India, but they, by no means, can compensate the heavy duty rain-bearing clouds that march from the eastern coast to the rest of the country.

"The number of low pressure systems that form over the Bay of Bengal would decline by 60% in a warmer scenario and there is a northward shift of the genesis area for these low pressure systems," team leader R S Ajaymohan from New York University, Abu Dhabi told DH.

Ajaymohan and his colleagues from Indian Institute of Tropical Meteorology, Pune; Indian Institute of Technology, Delhi; University of California, Berkeley and Lawrence Berkeley National Laboratory used monthly sea surface temperatures to model past and future low pressure system (LPS) in India. These seasonal storms are prominent and produce more than half of the region's precipitation.

Using a high-resolution atmospheric model, the authors simulated LPS activity from 1981 to 2005 and during the later part of the 21st century, from 2071 to 2095.

Societal impact

They not only observed a 60% decline in the formation of low pressure zone over the bay, but an overall 45% decline in LPS activity (calculated after taking into account sea wind speed as well). Also, there will be 10% increase in the number of LPS that form over the Indian land.

A shift in monsoon activity that dries central India and increases the likelihood of extreme rainfall in northern India (Jharkhand, Bihar, Chhattisgarh, and Uttarakhand) would have major societal impact, the researchers reported in the Proceedings of National Academy of Sciences on February 27.