Monday, 30th October 2017

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Rain alert on rising temperatures

Rising global temperatures will lead to a 60 per cent fall in the number of low pressure storms over the Bay of Bengal that serve as key rain-bearing engines during the monsoon, climate scientists have predicted.

By G.S. Mudur
  • Published 28.02.18
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New Delhi: Rising global temperatures will lead to a 60 per cent fall in the number of low pressure storms over the Bay of Bengal that serve as key rain-bearing engines during the monsoon, climate scientists have predicted.

Their study, relying on computer simulations, has predicted a northward shift of the monsoon's wind patterns that the scientists say are likely to lead to a drier central India and an increase in the number of extreme rain events over northern India.

The scientists from government and academic institutions in India and the US, who published their findings on Monday in the journal Proceedings of the National Academy of Sciences, have cautioned that such changes in rainfall patterns could have societal impacts during the second half of the century.

Their analysis has suggested that under global warming, the enhanced contrast between the land and ocean temperatures will shift the monsoon wind circulation northward. Under the strongest warming scenarios, the core of the monsoon's jet-stream winds could shift by one degree latitude by the end of this century.

"The impact of even this one degree shift could be huge as it could result in shifts in rainfall patterns over the subcontinent," said Ravindran Ajayamohan, a senior scientist at the Centre for Prototype Climate Modelling at the New York University's Abu Dhabi campus, who led the research.

The shift is likely to translate into a 60 per cent drop in the formation of low pressure storms over the Bay of Bengal and a 10 per cent increase in low pressure storms over the northern Indian landmass.

"For good rainfall, we need low pressure systems to form over the sea," Ajayamohan said.

Every year during the monsoon season, low pressure storms build up over the Bay of Bengal, sucking up moisture from the sea and moving over land and delivering rain across the Indian peninsula for days.

"Low pressure systems that form over the land are limited by their moisture supply - they are short-lasting and don't bring enough rain," Ajayamohan said. The effect will be a drier central peninsular Indian region.

The changes in the low pressure systems are also expected to increase the occurrence of extreme rain events - unusually copious and continuous showers compressed to fewer than 24 hours over localised areas but with the potential to wreak havoc through flooding or landslides - in northern India.

Senior meteorologists in India say the fall in the numbers of low pressure storms over the Bay of Bengal is already evident.

"There has been a statistically significant decline in the numbers of low pressure systems during the monsoon season over the past 50 years," said Madhavan Rajeevan, a senior scientist.